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What was the first known flower meant for a flying pollinator insect?

What was the first known flower meant for a flying pollinator insect?


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I think flower ancestors were colorless and sugarless. The first flower then chanced upon using insects by attracting them. Has this flower been discovered and from what ancestors did it evolve from?


When Is A Pollinator Not A Pollinator? Tales From An Insect Crime Scene.

Danger looms for the lovely, red, trumpet-shaped blossoms of the scarlet gilia, a Rocky Mountain plant. Their nectar is in jeopardy. There are thieves among the bumblebees, and their larceny will prevent the sprightly hummingbirds from pollinating the gilia.

Rebecca E. Irwin and Alison K. Brody of the University of Vermont have been studying these bandits, known as nectar-robbing bumble bees (Bombus occidentalis) at the Rocky Mountain Biological Laboratory in Colorado. A study published in the July issue of Ecology highlights their research.

Past studies have shown that nectar robbing may in fact have a positive effect on the reproductive success of a plant. Some robbers can unknowingly aid in a plant's pollination when they brush up against floral reproductive structures. In this study, the researchers wanted to know if nectar robbing was detrimental to the scarlet gilia (Ipomopsis aggregata).

To study the bee's effects on the gilia, the researchers first studied the method by which the robber steals nectar from the plant's blossoms. The bee uses its spiky, toothed mouthparts to chew a hole through the side of the corolla, the petals that surround the inner parts of the flower. It then sucks the nectar out of this hole through a long, snout-like proboscis.

While this method provides ample nectar for the bee, there is none left for other winged creatures, such as the hummingbirds which migrate through the region.

This larceny also fails to pollinate the plant, a process that would likely occur after a visit from a hummingbird. Pollination in the gilia occurs only through interplant pollen transfer. For a plant to be successfully pollinated, the pollen of one plant must be transferred to the stigma of another, where it can fertilize the ovule and form seeds.

Nectar robbing, therefore, has the potential to be highly damaging to the plant's reproductive success. Since individual gilia plants bloom only once, estimates of lifetime reproductive success can be measured in a single season.

The researchers measured the rate of pollen transfer between the scarlet gilia plants by placing dye particles on flowers to imitate pollen. The number of dye particles deposited on flowers were compared in plants with low and high robbing rates. This was associated with the amount of pollen transferred by pollinators.

The researchers found that highly-robbed flowers donated and received fewer dye particles. This meant that less pollen transfer was occurring among those plants which were visited often by nectar robbers.

"The most probable explanation for the reduced fitness of nectar-robbed scarlet gilia is that these plants attract less pollinators," says Irwin. "Hummingbirds tend to avoid plants which are highly robbed, and visit less flowers on those plants. Our study shows that nectar-robbing does decrease reproductive success in the scarlet gilia, further research will elucidate the effect of floral larceny on the evolution of floral traits."

###Ecology is a peer-reviewed journal published eight times a year by the Ecological Society of America (ESA). Copies of the above article are available free of charge to the press through the Society's Public Affairs Office. Members of the press may also obtain copies of ESA's entire family of publications, which includes Ecology, Ecological Applications, Ecological Monographs, and Conservation Ecology. Others interested in copies of articles should contact the Reprint Department at the address in the masthead.

Founded in 1915, the Ecological Society of America (ESA) is a scientific, non-profit, organization with over 7000 members. Through ESA reports, journals, membership research, and expert testimony to Congress, ESA seeks to promote the responsible application of ecological data and principles to the solution of environmental problems. For more information about the Society and its activities, access ESA's web site at: http://esa.sdsc.edu.

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Flies

Radu Privantu/Flickr/CC BY 2.0

Many flies prefer to feed on flowers, and in doing so, provide essential pollination services to the plants they visit. Nearly half of the 150 fly families visit flowers. Flies are particularly important and efficient pollinators in environments where bees are less active, such as in alpine or arctic habitats.

Among the pollinating flies, hoverflies, from the family Syrphidae, are the reigning champions. The roughly 6,000 species known worldwide are also called flower flies, for their association with flowers, and many are bee or wasp mimics. Some hoverflies have a modified mouthpart, also called a proboscis, made for siphoning nectar from long, narrow flowers. And as an added bonus, about 40 percent of hoverflies bear larvae that prey on other insects, which thereby provide pest control services to the plant being pollinated. Hoverflies are the workhorses of the orchard. They pollinate a variety of fruit crops, such as apples, pears, cherries, plums, apricots, peaches, strawberries, raspberries, and blackberries.

Hoverflies are not the only pollinating flies out there. Other pollen-toting flies include some carrion and dung flies, tachinid flies, bee flies, small-headed flies, March flies, and blowflies.


Contents

Preservation Edit

Due to their external skeleton, the fossil history of insects is not entirely dependent on lagerstätte type preservation as for many soft-bodied organisms. However, with their small size and light build, insects have not left a particularly robust fossil record. Other than insects preserved in amber, most finds are terrestrial or near terrestrial sources and only preserved under very special conditions such as at the edge of freshwater lakes. While some 1/3 of known non-insect species are extinct fossils, due to the paucity of their fossil record, only 1/100th of known insects are extinct fossils. [7]

Insect fossils are often three dimensional preservations of the original fossil. Loose wings are a common type of fossil as the wings do not readily decay or digest, and are often left behind by predators. Fossilization will often preserve their outer appearance, contrary to vertebrate fossils whom are mostly preserved just as bony remains (or inorganic casts thereof). Due to their size, vertebrate fossils with the external aspect similarly preserved are rare, and most known cases are subfossils. [8] Fossils of insects, when preserved, are often preserved as three-dimensional, permineralized, and charcoalified replicas and as inclusions in amber and even within some minerals. Sometimes even their colour and patterning is still discernible. [9] Preservation in amber is however limited by large resin production by trees only evolving in the Mesozoic. [10] [11]

There is also abundant fossil evidence for the behavior of extinct insects, including feeding damage on fossil vegetation and in wood, fecal pellets, and nests in fossil soils. Such preservation is rare in vertebrate, and is mostly confined to footprints and coprolites. [12] : 42

Freshwater and marine insect fossils Edit

The common denominator among most deposits of fossil insects and terrestrial plants is the lake environment. Those insects that became preserved were either living in the fossil lake (autochthonous) or carried into it from surrounding habitats by winds, stream currents, or their own flight (allochthonous). Drowning and dying insects not eaten by fish and other predators settle to the bottom, where they may be preserved in the lake’s sediments, called lacustrine, under appropriate conditions. Even amber, or fossil resin from trees, requires a watery environment that is lacustrine or brackish in order to be preserved. Without protection in anoxic sediments, amber would gradually disintegrate it is never found buried in fossil soils. Various factors contribute greatly to what kinds of insects become preserved and how well, if indeed at all, including lake depth, temperature, and alkalinity type of sediments whether the lake was surrounded by forest or vast and featureless salt pans and if it was choked in anoxia or highly oxygenated.

There are some major exceptions to the lacustrine theme of fossil insects, the most famous being the Late Jurassic limestones from Solnhofen and Eichstätt, Germany, which are marine. These deposits are famous for pterosaurs and the earliest bird, Archaeopteryx. The limestones were formed by a very fine mud of calcite that settled within stagnant, hypersaline bays isolated from inland seas. Most organisms in these limestones, including rare insects, were preserved intact, sometimes with feathers and outlines of soft wing membranes, indicating that there was very little decay. The insects, however, are like casts or molds, having relief but little detail. In some cases iron oxides precipitated around wing veins, revealing better detail. [12] : 42

Compressions, impressions and mineralization Edit

There are many different ways insects can be fossilized and preserved including compressions and impressions, concretions, mineral replication, charcoalified (fusainized) remains, and their trace remains. Compressions and Impressions are the most extensive types of insect fossils, occurring in rocks from the Carboniferous to the Holocene. Impressions are like a cast or mold of a fossil insect, showing its form and even some relief, like pleating in the wings, but usually little or no color from the cuticle. Compressions preserve remains of the cuticle, so color distinguishes structure. In exceptional situations, microscopic features such as microtrichia on sclerites and wing membranes are even visible, but preservation of this scale also requires a matrix of exceptionally fine grain, such as in micritic muds and volcanic tuffs. Because arthropod sclerites are held together by membranes, which readily decompose, many fossil arthropods are known only by isolated sclerites. Far more desirable are complete fossils. Concretions are stones with a fossil at the core whose chemical composition differs from that of the surrounding matrix, usually formed as a result of mineral precipitation from decaying organisms. The most significant deposit consists of various localities of the Late Carboniferous Francis Creek Shale of the Carbondale Formation at Mazon Creek, Illinois, which are composed of shales and coal seams yielding oblong concretions. Within most concretions is a mold of an animal and sometimes a plant that is usually marine in origin.

When an insect is partly or wholly replaced by minerals, usually completely articulated and with three-dimensional fidelity, is called mineral replication. [12] This is also called petrifaction, as in petrified wood. Insects preserved this way are often, but not always, preserved as concretions, or within nodules of minerals that formed around the insect as its nucleus. Such deposits generally form where the sediments and water are laden with minerals, and where there is also quick mineralization of the carcass by coats of bacteria.

The insect fossil record extends back some 400 million years to the lower Devonian, while the Pterygotes (winged insects) underwent a major radiation in the Carboniferous. The Endopterygota underwent another major radiation in the Permian. Survivors of the mass extinction at the P-T boundary evolved in the Triassic to what are essentially the modern Insecta Orders that persist to modern times.

Most modern insect families appeared in the Jurassic, and further diversity probably in genera occurred in the Cretaceous. By the Tertiary, there existed many of what are still modern genera hence, most insects in amber are, indeed, members of extant genera. Insects diversified in only about 100 million years into essentially modern forms. [7]

Insect evolution is characterized by rapid adaptation due to selective pressures exerted by the environment and furthered by high fecundity. It appears that rapid radiations and the appearance of new species, a process that continues to this day, result in insects filling all available environmental niches.

The evolution of insects is closely related to the evolution of flowering plants. Insect adaptations include feeding on flowers and related structures, with some 20% of extant insects depending on flowers, nectar or pollen for their food source. This symbiotic relationship is even more paramount in evolution considering that more than 2/3 of flowering plants are insect pollinated. [13]

Insects, particularly mosquitoes and flies, are also vectors of many pathogens that may even have been responsible for the decimation or extinction of some mammalian species. [14]

Devonian Edit

The Devonian (419 to 359 million years ago) was a relatively warm period, and probably lacked any glaciers with reconstruction of tropical sea surface temperature from conodont apatite implying an average value of 30 °C (86 °F) in the Early Devonian. CO
2 levels dropped steeply throughout the Devonian period as the burial of the newly evolved forests drew carbon out of the atmosphere into sediments this may be reflected by a Mid-Devonian cooling of around 5 °C (9 °F). The Late Devonian warmed to levels equivalent to the Early Devonian while there is no corresponding increase in CO
2 concentrations, continental weathering increases (as predicted by warmer temperatures) further, a range of evidence, such as plant distribution, points to Late Devonian warming. [15] The continent Euramerica (or Laurussia) was created in the early Devonian by the collision of Laurentia and Baltica, which rotated into the natural dry zone along the Tropic of Capricorn, which is formed as much in Paleozoic times as nowadays by the convergence of two great atmospheric circulations, the Hadley cell and the Ferrel cell.

The oldest definitive insect fossil is the Devonian Rhyniognatha hirsti, estimated at 407 to 396 million years ago. [16] This species already possessed dicondylic (with two condyles, articulations) mandibles, a feature associated with winged insects, suggesting that wings may already have evolved at this time. Thus, the first insects probably appeared earlier, in the Silurian period. [16] [17] Like other insects of its time, Rhyniognatha presumably fed on plant sporophylls — which occur at the tips of branches and bear sporangia, the spore-producing organs. The insect’s anatomy might also give clues as to what it ate. The creature had large mandibles which may or may not have been used for hunting. [16]

In 2012, researchers found the first complete insect in the Late Devonian period (382 to 359 million years ago), in the Strud (Gesves, Belgium) environment from the Bois des Mouches Formation, Upper Famennian. It had unspecialized, 'orthopteroid' mouthparts, indicating an omnivorous diet. This discovery reduces a previous gap of 45 million years in the evolutionary history of insects, part of the arthropod gap (the 'gap' still occurs in the early Carboniferous, coinciding and extending past the Romer's gap for tetrapods, which may have been caused by low oxygen levels in the atmosphere). [18] Body segments, legs and antennae are visible however, genitalia were not preserved. The venerable species was named Strudiella devonica. [19] The insect has no wings, but it may be a juvenile. [19]

Carboniferous Edit

The Carboniferous ( 359 to 299 million years ago ) is famous for its wet, warm climates and extensive swamps of mosses, ferns, horsetails, and calamites. [17] Glaciations in Gondwana, triggered by Gondwana's southward movement, continued into the Permian and because of the lack of clear markers and breaks, the deposits of this glacial period are often referred to as Permo-Carboniferous in age. The cooling and drying of the climate led to the Carboniferous rainforest collapse (CRC). Tropical rain forests fragmented and then were eventually devastated by climate change. [20]

Remains of insects are scattered throughout the coal deposits, particularly of wings from cockroaches (Blattodea) [21] two deposits in particular are from Mazon Creek, Illinois and Commentry, France. [22] The earliest winged insects are from this time period (Pterygota), including the aforementioned Blattodea, Caloneurodea, primitive stem-group Ephemeropterans, Orthoptera, Palaeodictyopteroidea. [17] : 399 In 1940 (in Noble County, Oklahoma), a fossil of Meganeuropsis americana represented the largest complete insect wing ever found. [23] Juvenile insects are also known from the Carboniferous Period. [24]

Very early Blattopterans had a large, discoid pronotum and coriaceous forewings with a distinct CuP vein (a unbranched wing vein, lying near the claval fold and reaching the wing posterior margin). These were not true cockroaches, as they had an ovipositor, although through the Carboniferous, the ovipositor started to diminish. The orders Caloneurodea and Miomoptera are known, with Orthoptera and Blattodea to be among the earliest Neoptera developing from the upper Carboniferous to the Permian. These insects had wings with similar form and structure: small anal lobes. [17] : 399 Species of Orthoptera, or grasshoppers and related kin, is an ancient order that still exist till today extending from this time period. From which time even the distinctive synapomorphy of saltatorial, or adaptive for jumping, hind legs is preserved.

Palaeodictyopteroidea is a large and diverse group that includes 50% of all known Paleozoic insects. [12] Containing many of the primitive features of the time: very long cerci, an ovipositor, and wings with little or no anal lobe. Protodonata, as its name implies, is a primitive paraphyletic group similar to Odonata although lacks distinct features such as a nodus, a pterostigma and an arculus. Most were only slightly larger than modern dragonflies, but the group does include the largest known insects, such as the late Carboniferous Meganeura monyi, Megatypus, and the even larger later Permian Meganeuropsis permiana, with wingspans of up to 71 cm (2 ft 4 in). They were probably the top predators for some 100 million years [17] : 400 and far larger than any present-day insects. Their nymphs must also have reached a very impressive size. This gigantism may have been due to higher atmospheric oxygen-levels (up to 80% above modern levels during the Carboniferous) that allowed increased respiratory efficiency relative to today. The lack of flying vertebrates could have been another factor.

Permian Edit

The Permian ( 299 to 252 million years ago ) was a relatively short time period, during which all the Earth's major land masses were collected into a single supercontinent known as Pangaea. Pangaea straddled the equator and extended toward the poles, with a corresponding effect on ocean currents in the single great ocean ("Panthalassa", the "universal sea"), and the Paleo-Tethys Ocean, a large ocean that was between Asia and Gondwana. The Cimmeria continent rifted away from Gondwana and drifted north to Laurasia, causing the Paleo-Tethys to shrink. [17] : 400 At the end of the Permian, the biggest mass extinction in history occurred, collectively called the Permian–Triassic extinction event: 30% of all insect species became extinct this is one of three known mass insect extinctions in Earth's history. [25]

2007 study based on DNA of living beetles and maps of likely beetle evolution indicated that beetles may have originated during the Lower Permian, up to 299 million years ago . [26] In 2009, a fossil beetle was described from the Pennsylvanian of Mazon Creek, Illinois, pushing the origin of the beetles to an earlier date, 318 to 299 million years ago . [27] Fossils from this time have been found in Asia and Europe, for instance in the red slate fossil beds of Niedermoschel near Mainz, Germany. [28] Further fossils have been found in Obora, Czech Republic and Tshekarda in the Ural mountains, Russia. [29] More discoveries from North America were made in the Wellington Formation of Oklahoma and were published in 2005 and 2008. [25] [30] Some of the most important fossil deposits from this era are from Elmo, Kansas (260 mya) others include New South Wales, Australia (240 mya) and central Eurasia (250 mya). [17] : 400

During this time, many of the species from the Carboniferous diversified, and many new orders developed, including: Protelytroptera, primitive relatives of Plecoptera (Paraplecoptera), Psocoptera, Mecoptera, Coleoptera, Raphidioptera, and Neuroptera, the last four being the first definitive records of the Holometabola. [17] : 400 By the Pennsylvanian and well into the Permian, by far the most successful were primitive Blattoptera, or relatives of cockroaches. Six fast legs, two well-developed folding wings, fairly good eyes, long, well-developed antennae (olfactory), an omnivorous digestive system, a receptacle for storing sperm, a chitin skeleton that could support and protect, as well as a form of gizzard and efficient mouth parts, gave it formidable advantages over other herbivorous animals. About 90% of insects were cockroach-like insects ("Blattopterans"). [31] The dragonflies Odonata were the dominant aerial predator and probably dominated terrestrial insect predation as well. True Odonata appeared in the Permian [32] [33] and all are amphibian. Their prototypes are the oldest winged fossils, [34] go back to the Devonian, and are different from other wings in every way. [35] Their prototypes may have had the beginnings of many modern attributes even by late Carboniferous and it is possible that they even captured small vertebrates, for some species had a wing span of 71 cm. [33]

The oldest known insect that resembles species of Coleoptera date back to the Lower Permian ( 270 million years ago ), though they instead have 13-segmented antennae, elytra with more fully developed venation and more irregular longitudinal ribbing, and an abdomen and ovipositor extending beyond the apex of the elytra. The oldest true beetle would have features that include 11-segmented antennae, regular longitudinal ribbing on the elytra, and having genitalia that are internal. [25] The earliest beetle-like species had pointed, leather like forewings with cells and pits. Hemiptera, or true bugs had appeared in the form of Arctiniscytina and Paraknightia. The later had expanded parapronotal lobes, a large ovipositor, and forewings with unusual venation, possibly diverging from Blattoptera. The orders Raphidioptera and Neuroptera are grouped together as Neuropterida. The one family of putative Raphidiopteran clade (Sojanoraphidiidae) has been controversially placed as so. Although the group had a long ovipositor distinctive to this order and a series of short crossveins, however with a primitive wing venation. Early families of Plecoptera had wing venation consistent with the order and its recent descendants. [17] : 186 Psocoptera was first appeared in the Permian period, they are often regarded as the most primitive of the hemipteroids. [36]

Triassic Edit

The Triassic ( 252 to 201 million years ago ) was a period when arid and semiarid savannas developed and when the first mammals, dinosaurs, and pterosaurs also appeared. During the Triassic, almost all the Earth's land mass was still concentrated into Pangaea. From the east a vast gulf entered Pangaea, the Tethys sea. The remaining shores were surrounded by the world-ocean known as Panthalassa. The supercontinent Pangaea was rifting during the Triassic—especially late in the period—but had not yet separated. [25]

The climate of the Triassic was generally hot and dry, forming typical red bed sandstones and evaporites. There is no evidence of glaciation at or near either pole in fact, the polar regions were apparently moist and temperate, a climate suitable for reptile-like creatures. Pangaea's large size limited the moderating effect of the global ocean its continental climate was highly seasonal, with very hot summers and cold winters. It probably had strong, cross-equatorial monsoons. [37]

As a consequence of the P-Tr Mass Extinction at the border of Permian and Triassic, there is only little fossil record of insects including beetles from the Lower Triassic. [38] However, there are a few exemptions, like in Eastern Europe: At the Babiy Kamen site in the Kuznetsk Basin numerous beetle fossils were discovered, even entire specimen of the infraorders Archostemata (i.e., Ademosynidae, Schizocoleidae), Adephaga (i.e., Triaplidae, Trachypachidae) and Polyphaga (i.e., Hydrophilidae, Byrrhidae, Elateroidea) and in nearly a perfectly preserved condition. [39] However, species from the families Cupedidae and Schizophoroidae are not present at this site, whereas they dominate at other fossil sites from the Lower Triassic. Further records are known from Khey-Yaga, Russia in the Korotaikha Basin. [25]

Around this time, during the Late Triassic, mycetophagous, or fungus feeding species of beetle (i.e., Cupedidae) appear in the fossil record. In the stages of the Upper Triassic representatives of the algophagous, or algae feeding species (i.e., Triaplidae and Hydrophilidae) begin to appear, as well as predatory water beetles. The first primitive weevils appear (i.e., Obrienidae), as well as the first representatives of the rove beetles (i.e., Staphylinidae), which show no marked difference in physique compared to recent species. [25] This was also around the first time evidence of diverse freshwater insect fauna appeared.

Some of the oldest living families also appear around during the Triassic. Hemiptera included the Cercopidae, the Cicadellidae, the Cixiidae, and the Membracidae. Coleoptera included the Carabidae, the Staphylinidae, and the Trachypachidae. Hymenoptera included the Xyelidae. Diptera included the Anisopodidae, the Chironomidae, and the Tipulidae. The first Thysanoptera appeared as well.

The first true species of Diptera are known from the Middle Triassic, becoming widespread during the Middle and Late Triassic . A single large wing from a species of Diptera in the Triassic (10 mm instead of usual 2–6 mm) was found in Australia (Mt. Crosby). This family Tilliardipteridae, despite of the numerous 'tipuloid' features, should be included in Psychodomorpha sensu Hennig on account of loss of the convex distal 1A reaching wing margin and formation of the anal loop. [40]

Jurassic Edit

The Jurassic ( 201 to 145 million years ago ) was important in the development of birds, one of the insects' major predators. During the early Jurassic period, the supercontinent Pangaea broke up into the northern supercontinent Laurasia and the southern supercontinent Gondwana the Gulf of Mexico opened in the new rift between North America and what is now Mexico's Yucatan Peninsula. The Jurassic North Atlantic Ocean was relatively narrow, while the South Atlantic did not open until the following Cretaceous Period, when Gondwana itself rifted apart. [41]

The global climate during the Jurassic was warm and humid. Similar to the Triassic, there were no larger landmasses situated near the polar caps and consequently, no inland ice sheets existed during the Jurassic. Although some areas of North and South America and Africa stayed arid, large parts of the continental landmasses were lush. The laurasian and the gondwanian fauna differed considerably in the Early Jurassic. Later it became more intercontinental and many species started to spread globally. [25]

There are many important sites from the Jurassic, with more than 150 important sites with beetle fossils, the majority being situated in Eastern Europe and North Asia. In North America and especially in South America and Africa the number of sites from that time period is smaller and the sites have not been exhaustively investigated yet. Outstanding fossil sites include Solnhofen in Upper Bavaria, Germany, [42] Karatau in South Kazakhstan, [43] the Yixian Formation in Liaoning, North China [44] as well as the Jiulongshan Formation and further fossil sites in Mongolia. In North America there are only a few sites with fossil records of insects from the Jurassic, namely the shell limestone deposits in the Hartford basin, the Deerfield basin and the Newark basin. [25] [45] Numerous deposits of other insects occur in Europe and Asia. Including Grimmen and Solnhofen, German Solnhofen being famous for findings of the earliest birds (i.e. Archaeopteryx). Others include Dorset, England Issyk-Kul, Kirghizstan and the most productive site of all, Karatau, Kazakhstan. [ citation needed ]

During the Jurassic there was a dramatic increase in the known diversity of family-level Coleoptera. [25] This includes the development and growth of carnivorous and herbivorous species. Species of the superfamily Chrysomeloidea are believed to have developed around the same time, which include a wide array of plant host ranging from cycads and conifers, to angiosperms. [46] : 186 Close to the Upper Jurassic, the portion of the Cupedidae decreased, however at the same time the diversity of the early plant eating, or phytophagous species increased. Most of the recent phytophagous species of Coleoptera feed on flowering plants or angiosperms.

Cretaceous Edit

The Cretaceous ( 145 to 66 million years ago ) had much of the same insect fauna as the Jurassic until much later on. During the Cretaceous, the late-Paleozoic-to-early-Mesozoic supercontinent of Pangaea completed its tectonic breakup into present day continents, although their positions were substantially different at the time. As the Atlantic Ocean widened, the convergent-margin orogenies that had begun during the Jurassic continued in the North American Cordillera, as the Nevadan orogeny was followed by the Sevier and Laramide orogenies. Though Gondwana was still intact in the beginning of the Cretaceous, it broke up as South America, Antarctica and Australia rifted away from Africa (though India and Madagascar remained attached to each other) thus, the South Atlantic and Indian Oceans were newly formed. Such active rifting lifted great undersea mountain chains along the welts, raising eustatic sea levels worldwide. To the north of Africa the Tethys Sea continued to narrow. Broad shallow seas advanced across central North America (the Western Interior Seaway) and Europe, then receded late in the period, leaving thick marine deposits sandwiched between coal beds.

At the peak of the Cretaceous transgression, one-third of Earth's present land area was submerged. [47] The Berriasian epoch showed a cooling trend that had been seen in the last epoch of the Jurassic. There is evidence that snowfalls were common in the higher latitudes and the tropics became wetter than during the Triassic and Jurassic. [48] Glaciation was however restricted to alpine glaciers on some high-latitude mountains, though seasonal snow may have existed farther south. Rafting by ice of stones into marine environments occurred during much of the Cretaceous but evidence of deposition directly from glaciers is limited to the Early Cretaceous of the Eromanga Basin in southern Australia. [49] [50]

There are a large number of important fossil sites worldwide containing beetles from the Cretaceous. Most of them are located in Europe and Asia and belong to the temperate climate zone during the Cretaceous. A few of the fossil sites mentioned in the chapter Jurassic also shed some light on the early cretaceous beetle fauna (e.g. the Yixian formation in Liaoning, North China). [44] Further important sites from the Lower Cretaceous include the Crato Fossil Beds in the Araripe basin in the Ceará, North Brazil as well as overlying Santana formation, with the latter was situated near the paleoequator, or the position of the earth's equator in the geologic past as defined for a specific geologic period. In Spain there are important sites near Montsec and Las Hoyas. In Australia the Koonwarra fossil beds of the Korumburra group, South Gippsland, Victoria is noteworthy. Important fossil sites from the Upper Cretaceous are Kzyl-Dzhar in South Kazakhstan and Arkagala in Russia. [25]

During the Cretaceous the diversity of Cupedidae and Archostemata decreased considerably. Predatory ground beetles (Carabidae) and rove beetles (Staphylinidae) began to distribute into different patterns: whereas the Carabidae predominantly occurred in the warm regions, the Staphylinidae and click beetles (Elateridae) preferred many areas with temperate climate. Likewise, predatory species of Cleroidea and Cucujoidea, hunted their prey under the bark of trees together with the jewel beetles (Buprestidae). The jewel beetles diversity increased rapidly during the Cretaceous, as they were the primary consumers of wood, [51] while longhorn beetles (Cerambycidae) were rather rare and their diversity increased only towards the end of the Upper Cretaceous. [25] The first coprophagous beetles have been recorded from the Upper Cretaceous, [52] and are believed to have lived on the excrement of herbivorous dinosaurs, however there is still a discussion, whether the beetles were always tied to mammals during its development. [53] Also, the first species with an adaption of both larvae and adults to the aquatic lifestyle are found. Whirligig beetles (Gyrinidae) were moderately diverse, although other early beetles (i.e., Dytiscidae) were less, with the most widespread being the species of Coptoclavidae, which preyed on aquatic fly larvae. [25]

Paleogene Edit

There are many fossils of beetles known from this era, though the beetle fauna of the Paleocene is comparatively poorly investigated. In contrast, the knowledge on the Eocene beetle fauna is very good. The reason is the occurrence of fossil insects in amber and clay slate sediments. Amber is fossilized tree resin, that means it consists of fossilized organic compounds, not minerals. Different amber is distinguished by location, age and species of the resin producing plant. For the research on the Oligocene beetle fauna, Baltic and Dominican amber is most important. [25] Even with the insect fossils record in general lacking, the most diverse deposit being from the Fur Formation, Denmark including giant ants and primitive moths (Noctuidae). [17] : 402

The first butterflies are from the Upper Paleogene, while most, like beetles, already had recent genera and species already existed during the Miocene, however, their distribution differed considerably from today's. [17] : 402

Neogene Edit

The most important sites for beetle fossils of the Neogene are situated in the warm temperate and to subtropical zones. Many recent genera and species already existed during the Miocene, however, their distribution differed considerably from today's. One of the most important fossil sites for insects of the Pliocene is Willershausen near Göttingen, Germany with excellently preserved beetle fossils of various families (longhorn beetles, weevils, ladybugs and others) as well as representatives of other orders of insects. [54] In the Willershausen clay pit so far 35 genera from 18 beetle families have been recorded, of which six genera are extinct. [55] The Pleistocene beetle fauna is relatively well known, who used the composition of the beetle fauna to reconstruct climate conditions in the Rocky Mountains and on Beringia, the former land bridge between Asia and North America. [56] [57]

A report in November 2014 unambiguously places the insects in one clade, with the remipedes as the nearest sister clade. [58] This study resolved insect phylogeny of all extant insect orders, and provides "a robust phylogenetic backbone tree and reliable time estimates of insect evolution." [58] Finding strong support for the closest living relatives of the hexapods had proven challenging due to convergent adaptations in a number of arthropod groups for living on land. [59]

In 2008, researchers at Tufts University uncovered what they believe is the world's oldest known full-body impression of a primitive flying insect, a 300 million-year-old specimen from the Carboniferous Period. [61] The oldest definitive insect fossil is the Devonian Rhyniognatha hirsti, from the 396 million year old Rhynie chert. It may have superficially resembled a modern-day silverfish insect. This species already possessed dicondylic mandibles (two articulations in the mandible), a feature associated with winged insects, suggesting that wings may already have evolved at this time. Thus, the first insects probably appeared earlier, in the Silurian period. [16] [62] There have been four super radiations of insects: beetles (evolved around 300 million years ago ), flies (evolved around 250 million years ago ), moths and wasps (evolved around 150 million years ago ). [12] These four groups account for the majority of described species. The flies and moths along with the fleas evolved from the Mecoptera. The origins of insect flight remain obscure, since the earliest winged insects currently known appear to have been capable fliers. Some extinct insects had an additional pair of winglets attaching to the first segment of the thorax, for a total of three pairs. There is no evidence that suggests that the insects were a particularly successful group of animals before they evolved to have wings. [12]

Evolutionary relationships Edit

Insects are prey for a variety of organisms, including terrestrial vertebrates. The earliest vertebrates on land existed 350 million years ago and were large amphibious piscivores, through gradual evolutionary change, insectivory was the next diet type to evolve. [20] Insects were among the earliest terrestrial herbivores and acted as major selection agents on plants. [5] Plants evolved chemical defenses against this herbivory and the insects in turn evolved mechanisms to deal with plant toxins. Many insects make use of these toxins to protect themselves from their predators. Such insects often advertise their toxicity using warning colors. [5] This successful evolutionary pattern has also been utilized by mimics. Over time, this has led to complex groups of coevolved species. Conversely, some interactions between plants and insects, like pollination, are beneficial to both organisms. Coevolution has led to the development of very specific mutualisms in such systems.

Orthoptera (grasshoppers and crickets)

Traditional morphology-based or appearance-based systematics has usually given Hexapoda the rank of superclass, [65] and identified four groups within it: insects (Ectognatha), springtails (Collembola), Protura and Diplura, the latter three being grouped together as Entognatha on the basis of internalized mouth parts. Supraordinal relationships have undergone numerous changes with the advent of methods based on evolutionary history and genetic data. A recent theory is that Hexapoda is polyphyletic (where the last common ancestor was not a member of the group), with the entognath classes having separate evolutionary histories from Insecta. [66] Many of the traditional appearance-based taxa have been shown to be paraphyletic, so rather than using ranks like subclass, superorder and infraorder, it has proved better to use monophyletic groupings (in which the last common ancestor is a member of the group). The following represents the best supported monophyletic groupings for the Insecta.

Insects can be divided into two groups historically treated as subclasses: wingless insects, known as Apterygota, and winged insects, known as Pterygota. The Apterygota consist of the primitively wingless order of the silverfish (Thysanura). Archaeognatha make up the Monocondylia based on the shape of their mandibles, while Thysanura and Pterygota are grouped together as Dicondylia. It is possible that the Thysanura themselves are not monophyletic, with the family Lepidotrichidae being a sister group to the Dicondylia (Pterygota and the remaining Thysanura). [67] [68]

Paleoptera and Neoptera are the winged orders of insects differentiated by the presence of hardened body parts called sclerites also, in Neoptera, muscles that allow their wings to fold flatly over the abdomen. Neoptera can further be divided into incomplete metamorphosis-based (Polyneoptera and Paraneoptera) and complete metamorphosis-based groups. It has proved difficult to clarify the relationships between the orders in Polyneoptera because of constant new findings calling for revision of the taxa. For example, Paraneoptera has turned out to be more closely related to Endopterygota than to the rest of the Exopterygota. The recent molecular finding that the traditional louse orders Mallophaga and Anoplura are derived from within Psocoptera has led to the new taxon Psocodea. [69] Phasmatodea and Embiidina have been suggested to form Eukinolabia. [70] Mantodea, Blattodea and Isoptera are thought to form a monophyletic group termed Dictyoptera. [71]

It is likely that Exopterygota is paraphyletic in regard to Endopterygota. Matters that have had a lot of controversy include Strepsiptera and Diptera grouped together as Halteria based on a reduction of one of the wing pairs – a position not well-supported in the entomological community. [72] The Neuropterida are often lumped or split on the whims of the taxonomist. Fleas are now thought to be closely related to boreid mecopterans. [73] Many questions remain to be answered when it comes to basal relationships amongst endopterygote orders, particularly Hymenoptera.

The study of the classification or taxonomy of any insect is called systematic entomology. If one works with a more specific order or even a family, the term may also be made specific to that order or family, for example systematic dipterology.

The oldest definitive insect fossil is the Devonian Rhyniognatha hirsti, estimated at 396-407 million years old. [16] This species already possessed dicondylic mandibles, a feature associated with winged insects, suggesting that wings may already have evolved at this time. Thus, the first insects probably appeared earlier, in the Silurian period. [16]

The subclass Apterygota (wingless insects) is now considered artificial as the silverfish (order Thysanura) are more closely related to Pterygota (winged insects) than to bristletails (order Archaeognatha). For instance, just like flying insects, Thysanura have so-called dicondylic mandibles, while Archaeognatha have monocondylic mandibles. The reason for their resemblance is not due to a particularly close relationship, but rather because they both have kept a primitive and original anatomy in a much higher degree than the winged insects. The most primitive order of flying insects, the mayflies (Ephemeroptera), are also those who are most morphologically and physiologically similar to these wingless insects. Some mayfly nymphs resemble aquatic thysanurans.

Modern Archaeognatha and Thysanura still have rudimentary appendages on their abdomen called styli, while more primitive and extinct insects known as Monura had much more developed abdominal appendages. The abdominal and thoracic segments in the earliest terrestrial ancestor of the insects would have been more similar to each other than they are today, and the head had well-developed compound eyes and long antennae. Their body size is not known yet. As the most primitive group today, Archaeognatha, is most abundant near the coasts, it could mean that this was the kind of habitat where the insect ancestors became terrestrial. But this specialization to coastal niches could also have a secondary origin, just as could their jumping locomotion, as it is the crawling Thysanura who are considered to be most original (plesiomorphic). By looking at how primitive cheliceratan book gills (still seen in horseshoe crabs) evolved into book lungs in primitive spiders and finally into tracheae in more advanced spiders (most of them still have a pair of book lungs intact as well), it is possible the trachea of insects was formed in a similar way, modifying gills at the base of their appendages.

So far, no published research suggests that insects were a particularly successful group prior to their evolution of wings. [74]

Odonata Edit

The Odonata (dragonflies) are also a good candidate as the oldest living member of the Pterygota. Mayflies are morphologically and physiologically more basal, but the derived characteristics of dragonflies could have evolved independently in their own direction for a long time. It seems that orders with aquatic nymphs or larvae become evolutionarily conservative once they had adapted to water. If mayflies made it to the water first, this could partly explain why they are more primitive than dragonflies, even if dragonflies have an older origin. Similarly, stoneflies retain the most basal traits of the Neoptera, but they were not necessarily the first order to branch off. This also makes it less likely that an aquatic ancestor would have the evolutionary potential to give rise to all the different forms and species of insects that we know today.

Dragonfly nymphs have a unique labial "mask" used for catching prey, and the imago has a unique way of copulating, using a secondary male sex organ on the second abdominal segment. It looks like abdominal appendages modified for sperm transfer and direct insemination have occurred at least twice in insect evolution, once in Odonata and once in the other flying insects. If these two different methods are the original ways of copulating for each group, it is a strong indication that it is the dragonflies who are the oldest, not the mayflies. There is still not agreement about this. Another scenario is that abdominal appendages adapted for direct insemination have evolved three times in insects once Odonata, once in mayflies and once in the Neoptera, both mayflies and Neoptera choosing the same solution. If so, it is still possible that mayflies are the oldest order among the flying insects. The power of flight is assumed to have evolved only once, suggesting sperm was still transferred indirectly in the earliest flying insects.

One possible scenario on how direct insemination evolved in insects is seen in scorpions. The male deposits a spermatophore on the ground, locks its claws with the female's claws and then guides her over his packet of sperm, making sure it comes in contact with her genital opening. When the early (male) insects laid their spermatophores on the ground, it seems likely that some of them used the clasping organs at the end of their body to drag the female over the package. The ancestors of Odonata evolved the habit of grabbing the female behind her head, as they still do today. This action, rather than not grasping the female at all, would have increased the male's chances of spreading its genes. The chances would be further increased if they first attached their spermatophore safely on their own abdomen before they placed their abdominal claspers behind the female's head the male would then not let the female go before her abdomen had made direct contact with his sperm storage, allowing the transfer of all sperm.

This also meant increased freedom in searching for a female mate because the males could now transport the packet of sperm elsewhere if the first female slipped away. This ability would eliminate the need to either wait for another female at the site of the deposited sperm packet or to produce a new packet, wasting energy. Other advantages include the possibility of mating in other, safer places than flat ground, such as in trees or bushes.

If the ancestors of the other flying insects evolved the same habit of clasping the female and dragging her over their spermatophore, but posterior instead of anterior like the Odonata does, their genitals would come very close to each other. And from there on, it would be a very short step to modify the vestigial appendages near the male genital opening to transfer the sperm directly into the female. The same appendages the male Odonata use to transfer their sperm to their secondary sexual organs at the front of their abdomen. All insects with an aquatic nymphal or larval stage seem to have adapted to water secondarily from terrestrial ancestors. Of the most primitive insects with no wings at all, Archaeognatha and Thysanura, all members live their entire life cycle in terrestrial environments. As mentioned previously, Archaeognatha were the first to split off from the branch that led to the winged insects (Pterygota), and then the Thysanura branched off. This indicates that these three groups (Archaeognatha, Thysanura and Pterygota) have a common terrestrial ancestor, which probably resembled a primitive model of Apterygota, was an opportunistic generalist and laid spermatophores on the ground instead of copulating, like Thysanura still do today. If it had feeding habits similar to the majority of apterygotes of today, it lived mostly as a decomposer.

One should expect that a gill breathing arthropod would modify its gills to breathe air if it were adapting to terrestrial environments, and not evolve new respiration organs from bottom up next to the original and still functioning ones. Then comes the fact that insect (larva and nymph) gills are actually a part of a modified, closed trachea system specially adapted for water, called tracheal gills. The arthropod trachea can only arise in an atmosphere and as a consequence of the adaptations of living on land. This too indicates that insects are descended from a terrestrial ancestor.

And finally when looking at the three most primitive insects with aquatic nymphs (called naiads: Ephemeroptera, Odonata and Plecoptera), each order has its own kind of tracheal gills that are so different from one another that they must have separate origins. This would be expected if they evolved from land-dwelling species. This means that one of the most interesting parts of insect evolution is what happened between the Thysanura-Pterygota split and the first flight.

The origin of insect flight remains obscure, since the earliest winged insects currently known appear to have been capable fliers. Some extinct insects (e.g. the Palaeodictyoptera) had an additional pair of winglets attached to the first segment of the thorax, for a total of three pairs.

The wings themselves are sometimes said to be highly modified (tracheal) gills. [75] By comparing a well-developed pair of gill blades in mayfly naiads and a reduced pair of hind wings on the adults, it is not hard to imagine that the mayfly gills (tergaliae) and insect wings have a common origin, and newer research also supports this. [76] [77] Specifically, genetic research on mayflies has revealed that the gills and insect wings both may have originated from insect legs. [78] The tergaliae are not found in any other order of insects, and they have evolved in different directions with time. In some nymphs/naiads the most anterior pair has become sclerotized and works as a gill cover for the rest of the gills. Others can form a large sucker, be used for swimming or modified into other shapes. But it doesn't have to mean that these structures were originally gills. It could also mean that the tergaliae evolved from the same structures which gave rise to the wings, and that flying insects evolved from a wingless terrestrial species with pairs of plates on its body segments: three on the thorax and nine on the abdomen (mayfly nymphs with nine pairs of tergaliae on the abdomen exist, but so far no living or extinct insects with plates on the last two segments have been found). If these were primary gills, it would be a mystery why they should have waited so long to be modified when we see the different modifications in modern mayfly nymphs.

Theories Edit

When the first forests arose on Earth, new niches for terrestrial animals were created. Spore-feeders and others who depended on plants and/or the animals living around them would have to adapt too to make use of them. In a world with no flying animals, it would probably just be a matter of time before some arthropods who were living in the trees evolved paired structures with muscle attachments from their exoskeleton and used them for gliding, one pair on each segment. Further evolution in this direction would give bigger gliding structures on their thorax and gradually smaller ones on their abdomen. Their bodies would have become stiffer while thysanurans, which didn't evolve flight, kept their flexible abdomen.

Mayfly nymphs must have adapted to water while they still had the "gliders" on their abdomen intact. So far there is no concrete evidence to support this theory either, but it is one that offers an explanation for the problems of why presumably aquatic animals evolved in the direction they did.

Leaping and arboreal insects seems like a good explanation for this evolutionary process for several reasons. Because early winged insects were lacking the sophisticated wing folding mechanism of neopterous insects, they must have lived in the open and not been able to hide or search for food under leaves, in cracks, under rocks and other such confined spaces. In these old forests there weren't many open places where insects with huge structures on their back could have lived without experiencing huge disadvantages. If insects got their wings on land and not in water, which clearly seems to be the case, the tree canopies would be the most obvious place where such gliding structures could have emerged, in a time when the air was a new territory.

The question is if the plates used for gliding evolved from "scratch" or by modifying already existing anatomical details. The thorax in Thysanura and Archaeognatha are known to have some structures connected to their trachea which share similarities to the wings of primitive insects. This suggests the origin of the wings and the spiracles are related.

Gliding requires universal body modifications, as seen in present-day vertebrates such as some rodents and marsupials, which have grown wide, flat expansions of skin for this purpose. The flying dragons (genus Draco) of Indonesia has modified its ribs into gliders, and even some snakes can glide through the air by spreading their ribs. The main difference is that while vertebrates have an inner skeleton, primitive insects had a flexible and adaptive exoskeleton.

Some animals would be living in the trees, as animals are always taking advantage of all available niches, both for feeding and protection. At the time, the reproductive organs were by far the most nutritious part of the plant, and these early plants show signs of arthropod consumption and adaptations to protect themselves, for example by placing their reproductive organs as high up as possible. But there will always be some species who will be able to cope with that by following their food source up the trees. Knowing that insects were terrestrial at that time and that some arthropods (like primitive insects) were living in the tree crowns, it seems less likely that they would have developed their wings down on the ground or in the water.

In a three dimensional environment such as trees, the ability to glide would increase the insects' chances to survive a fall, as well as saving energy. This trait has repeated itself in modern wingless species such as the gliding ants who are living an arboreal life. When the gliding ability first had originated, gliding and leaping behavior would be a logical next step, which would eventually be reflected in their anatomical design. The need to navigate through vegetation and to land safely would mean good muscle control over the proto-wings, and further improvements would eventually lead to true (but primitive) wings. While the thorax got the wings, a long abdomen could have served as a stabilizer in flight.

Some of the earliest flying insects were large predators: it was a new ecological niche. Some of the prey were no doubt other insects, as insects with proto-wings would have radiated into other species even before the wings were fully evolved. From this point on, the arms race could continue: the same predator/prey co-evolution which has existed as long as there have been predators and prey on earth both the hunters and the hunted were in need of improving and extending their flight skills even further to keep up with the other.

Insects that had evolved their proto-wings in a world without flying predators could afford to be exposed openly without risk, but this changed when carnivorous flying insects evolved. It is unknown when they first evolved, but once these predators had emerged they put a strong selection pressure on their victims and themselves. Those of the prey who came up with a good solution about how to fold their wings over their backs in a way that made it possible for them to live in narrow spaces would not only be able to hide from flying predators (and terrestrial predators if they were on the ground) but also to exploit a wide variety of niches that were closed to those who couldn't fold their wings in this way. And today the neopterous insects (those that can fold their wings back over the abdomen) are by far the most dominant group of insects.

The water-skimming theory suggests that skimming on the water surface is the origin of insect flight. [79] This theory is based on the fact that the first fossil insects, the Devonian Rhyniognatha hirsti, is thought to have possessed wings, even though the insects' closest evolutionary ties are with crustaceans, which are aquatic.

Mayflies Edit

Another primitive trait of the mayflies are the subimago no other insects have this winged yet sexually immature stage. A few specialized species have females with no subimago, but retain the subimago stage for males.

The reasons the subimago still exists in this order could be that there hasn't been enough selection pressure to get rid of it it also seems specially adapted to do the transition from water to air.

The male genitalia are not fully functional at this point. One reason for this could be that the modification of the abdominal appendages into male copulation organs emerged later than the evolution of flight. This is indicated by the fact that dragonflies have a different copulation organ than other insects.

As we know, in mayflies the nymphs and the adults are specialized for two different ways of living in the water and in the air. The only stage (instar) between these two is the subimago. In more primitive fossil forms, the preadult individuals had not just one instar but numerous ones (while the modern subimago do not eat, older and more primitive species with a subimagos were probably feeding in this phase of life too as the lines between the instars were much more diffuse and gradual than today). Adult form was reached several moults before maturity. They probably didn't have more instars after becoming fully mature. This way of maturing is how Apterygota do it, which moult even when mature, but not winged insects.

Modern mayflies have eliminated all the instars between imago and nymph, except the single instar called subimago, which is still not (at least not in the males) fully sexually mature. The other flying insects with incomplete metamorphosis (Exopterygota) have gone a little further and completed the trend here all the immature structures of the animal from the last nymphal stage are completed at once in a single final moult. The more advanced insects with larvae and complete metamorphosis (Endopterygota) have gone even further. An interesting theory is that the pupal stage is actually a strongly modified and extended stage of subimago, but so far it is nothing more than a theory. There are some insects within the Exopterygota, thrips and whiteflies (Aleyrodidae), who have evolved pupae-like stages too.

Distant ancestors Edit

The distant ancestor of flying insects, a species with primitive proto-wings, had a more or less ametabolous life-cycle and instars of basically the same type as thysanurans with no defined nymphal, subimago or adult stages as the individual became older. Individuals developed gradually as they were grew and moulting, but probably without major changes inbetween instars.

Modern mayfly nymphs do not acquire gills until after their first moult. Before this stage they are so small that they need no gills to extract oxygen from the water. This could be a trait from the common ancestor of all flyers. An early terrestrial insect would have no need for paired outgrowths from the body before it started to live in the trees (or in the water, for that matter), so it would not have any.

This would also affect the way their offspring looked like in the early instars, resembling earlier ametabolous generations even after they had started to adapt to a new way of living, in a habitat where they actually could have some good use for flaps along their body. Since they matured in the same way as thysanurans with plenty of moultings as they were growing and very little difference between the adults and much younger individuals (unlike modern insects, which are hemimetabolous or holometabolous), there probably wasn't much room for adapting into different niches depending on age and stage. Also, it would have been difficult for an animal already adapted to a niche to make a switch to a new niche later in life based on age or size differences alone when these differences were not significant.

So proto-insects had to specialize and focus their whole existence on improving a single lifestyle in a particular niche. The older the species and the single individuals became, the more would they differ from their original form as they adapted to their new lifestyles better than the generations before. The final body-structure was no longer achieved while still inside the egg, but continued to develop for most of a lifetime, causing a bigger difference between the youngest and oldest individuals. Assuming that mature individuals most likely mastered their new element better than did the nymphs who had the same lifestyle, it would appear to be an advantage if the immature members of the species reached adult shape and form as soon as possible. This may explain why they evolved fewer but more intense instars and a stronger focus on the adult body, and with greater differences between the adults and the first instars, instead of just gradually growing bigger as earlier generations had done. This evolutionary trend explains how they went from ametabolous to hemimetabolous insects.

Reaching maturity and a fully-grown body became only a part of the development process gradually a new anatomy and new abilities - only possible in the later stages of life - emerged. The anatomy insects were born and grew up with had limitations which the adults who had learned to fly didn't have. If they couldn't live their early life the way adults did, immature individuals had to adapt to the best way of living and surviving despite their limitations till the moment came when they could leave them behind. This would be a starting point in the evolution where imago and nymphs started to live in different niches, some more clearly defined than others. Also, a final anatomy, size and maturity reached at once with a single final nymphal stage meant less waste of time and energy, and also [ citation needed ] made a more complex adult body structure. These strategies obviously became very successful with time.


Pollinators

By proclamation, Secretary of the Interior Deb Haaland declares June 21-27, 2021, to be National Pollinator Week.

National Pollinator Week is an annual event celebrated internationally in support of pollinator health.

Bees, bats, birds and butterflies do us an important service: As they visit flowers to feed on nectar, they carry pollen from plant to plant. This movement of pollen from a flower’s male stamen to its female stigma — or that of the next flower — fertilizes plants and produces fruits and seeds.

Most of the world's flowering plants and crops depend on the hard-working insects and birds we call pollinators.

Without pollinators, we would miss out on many fruits, vegetables and nuts — not to mention chocolate and coffee.

But pollinators are in trouble.

A hummingbird hawk moth flies to thistle at Bombay Hook National Wildlife Refuge in Delaware. (Photo: Patricia McGuire/Share the Experience, 2019 contest)

For the past 25 years, many species of bees and other pollinators have experienced large drops in numbers. Among the causes:

  • Fewer places to feed and breed. Pollinator habitat is shrinking. As roads and developments have replaced meadows and wildlands, pollinators have lost feeding and nesting sites. Remaining patches of prairie and meadow have become more disconnected. That makes it harder for pollinators to reach new breeding sites or find better habitat.
  • Imported species and diseases. Invasive plants crowd out native ones, reducing food and shelter for pollinators. Disease-causing organisms— including viruses, fungi and bacteria — can spread from non-native to native pollinators. Other stressors, such as poor nutrition and pesticide exposure, may intensify the effect of diseases.
  • Pesticides. While pesticides can help control crop pests and invasive species, improper use can harm pollinators and other wildlife. Use pesticides only when necessary. Use the minimum amount required and target the application so that only the intended pest is affected.

Rising temperatures may be contributing to a decline in bumblebees. Numbers of North American bumblebees have fallen nearly 50 percent since 1974. The biggest losses have occurred in places where temperatures have risen the highest.

Other climate change effects — more flooding, shorter fire cycles and the spread of invasive species — threaten native habitats. This may directly affect pollinators if the host plant that a pollinator needs to survive is overtaken by another plant species.

For more information on threats to pollinators, see Status of Pollinators in North America,a 2007 report from the National Academy of Science.

Plight of the Monarch

A monarch butterfly feeds on rubber rabbitbrush at Seedskadee National Wildlife Refuge in Wyoming. (Photo: Tom Koerner/USFWS)

The monarch butterfly, probably the world&rsquos best-known butterfly, has become the symbol for a whole class of imperiled pollinators.

A monarch butterfly can travel up to 3,000 miles during fall migration. But the spectacular fall flight of millions of monarchs is threatened by loss of habitat in overwintering areas and throughout breeding and migration areas.

In recent decades, numbers of North American monarchs have plummeted. Both the eastern population (which overwinters in Mexico) and the western population (which overwinters in California) are down. Status reports are based on annual counts at overwintering sites.

From 1996 to 2020, the eastern monarch population dropped 88 percent, from an estimated 383 million to just under 45 million.

Since the 1980s, the western overwintering population has dropped more than 99 percent, from 4.5 million to 1,914 monarchs.

On December 15, 2020, the Fish and Wildlife Service announced a 12-month finding on a petition to list the monarch butterfly under the Endangered Species Act. After a thorough review of the monarch&rsquos status, the Service determined that listing is &ldquowarranted, but precluded&rdquo at this time because of higher-priority listing actions.

The Service is working with federal and state agencies, tribes and non-government groups to conserve monarchs. These efforts involve engaging the public in creating and restoring habitat for monarchs and other pollinators.

Threatened and Endangered Pollinators

The Fish and Wildlife Service and partners are helping to recover the threatened Oregon silverspot butterfly. (Photo: Peter Pearsall/USFWS)

Some 70 pollinator species are so imperiled that they qualify as threatened or endangered under the Endangered Species Act. See the list.

How the Fish and Wildlife Service Helps Pollinators

The Fish and Wildlife Service leads many efforts to stabilize and improve pollinator status. For example:

  • Works with states and partners to conserve and restore habitat for pollinators, including milkweed for monarch butterflies. The Partners for Fish and Wildlife Program provides technical and financial assistance to landowners interested in restoring wildlife habitat on their land. Since 1987, some 50,000 landowners have worked with Partners staff to complete 60,000 habitat restoration projects on 6 million acres.
  • Works to recover threatened and endangered species, including imperiled pollinators. For example, the Service and partners reintroduced the threatened Oregon silverspot butterfly to Nestucca Bay National Wildlife Refuge in 2017. The action helped the butterfly make a comeback on the Oregon coast.
  • Creates pollinator garden demonstration sites at wildlife refuges, fish hatcheries and community sites near refuges. For example, the Service's South Texas Refuge Complex (which includes Santa Ana, Lower Rio Grande and Laguna Atascosa Refuges) worked with 45 area schools, serving at least 33,000 students, to create schoolyard habitats featuring native pollinator-friendly plants.
  • Creates and maintains butterfly trails and gardens at dozens of wildlife refuges. One butterfly garden is at Florida&rsquos Pelican Island National Wildlife Refuge, the nation&rsquos first national wildlife refuge, established in 1903,
  • Collaborates with partners on the National Seed Strategy to make native seeds more available for restoration. From 2015 to 2020, the group oversaw more than 8,800 native seed collections. The Service is also a member of the Plant Conservation Alliance.
  • Supports national wildlife refuges in creating monarch waystations and participating in the Monarch Butterfly Sister Protected Area Program, a partnership of wildlife refuges and national parks in the United States and Canada, and natural protected areas in Mexico. The partnership was created by the Trilateral Committee for Wildlife and Ecosystem Conservation and Management.
  • Works with Mexico and Canada to research, conserve and restore pollinators, such as bats.
  • Collaborates with the North American Pollinator Protection Campaign, a consortium of government agencies, non-government organizations, educational institutions and businesses dedicated to pollinator conservation and education. The Service provides technical assistance in developing educational materials.
  • Supports the efforts of wildlife refuges to conserve and restore native grasslands and prairies, which provide habitat for pollinators. Neal Smith National Wildlife Refuge in Iowa is a leader in the restoration of tallgrass prairie and sedge meadow in the Midwest.

“Before” and “after” photos of a Partners for Fish and Wildlife prairie seeding project in Arkansas. (Photo: Mike Budd/USFWS)

How You Can Help

Gisela Chapa, then-manager of Santa Ana National Wildlife Refuge in Texas, helps elementary school students plant a pollinator garden. (Photo: Ian Shive/Tandem)

Here are some simple things you can do to help pollinators.

1) Plant a Pollinator Garden

To attract a variety of pollinators, include a selection of plants native to your region. Native milkweed is vital for monarch butterflies to grow, develop and reproduce. Check field guides to find out which plants local caterpillars eat. Find pollinator-friendly plants for your area. Contact your local or state native plant society for help. Your local agricultural extension service is also a good resource.

Other resources for native plants include the Lady Bird Johnson Wildflower Center, with lists of native plant suppliers and a resident horticulturalist to answer questions.

2) Provide Pollinator Nesting Habitat
Pollinators such as bees and hummingbirds need places to nest as well as plants to feed on. Creating these places is surprisingly easy. Overlook some bare patches at the edge of your lawn. Many native bees are ground nesters. They need well-drained bare soil to create burrows.

Other native bees are cavity nesters they make their homes in dead wood or brush. Leave plant stems, fallen logs or stumps for bees, beetles and flies to use for nesting. Allow some twigs and leaf litter to remain where they fall to provide overwinter shelter for many insect pollinators.

3) Avoid or Limit Pesticide Use
Make pesticides your option of last resort in battling weeds and crop and garden pests. Try these steps first.

  • Take no action and accept some pest damage.
  • Use physical controls. Hand-remove or trim pest-infested plants, or remove weeds and insect pests with garden gloves.
  • Use mechanical controls such as machine tilling, aerating, cutting or digging.
  • Cultivate healthy growing habits. Use clean weed-free and insect-free mulch. Create beneficial insect habitat. Rotate garden crops from year to year. Water the garden as needed, not on a schedule. Choose plants that have not been treated with pesticides.
  • Grow organically to encourage native pest predators such as lacewings and lady beetles.

Without milkweed — the host plant for the monarch — monarch caterpillars can’t survive. (Photo: Kate Miyamoto/USFWS)

Educator Resources

Bumblebees are efficient pollinators that use vibration to release pollen. (Photo: Mike Budd/USFWS)

Introduction to pollinators for use by nature centers, scouts, 4-H groups and others. &rdquoThe Birds and the Bees and . . .The Beetles. Why Care about Pollinators&rdquo
(PowerPoint 4 MB)

&ldquoWhat is the Buzz with Pollinators?&rdquo Facebook Live presentation from John Heinz National Wildlife Refuge at Tinicum in Pennsylvania


Of Assassin Bugs and Damselflies in the Summer Garden

If you happened to walk around the Heritage Garden in late June, the unusual blue color of the Moroccan mountain eryngo (pronounced eh-RING-go), Eryngium variifolium, probably caught your eye, and its peculiar perfume tickled your nose. It was also swarming with flying insects.

The odor was not lovely and sweet. I would describe it as similar to musty, molding fruit—not unpleasant, but certainly not a fragrance you would wear. It only lasted a few days, during which time it hosted an amazing number and variety of insects. I attempted to photograph and identify as many of them as I could. This was a lot harder than I expected, because the insects were in constant motion and most of them were small. I didn’t always capture the key features needed to identify them at the species level. In spite of this, you’ll see that that the variety was astounding. Let me introduce you to what I found at the Chicago Botanic Garden recently.

Carpenter bees are often confused with bumblebees because of similar size and coloring. The carpenter bee has a black abdomen and a black spot on the back of its thorax (middle section). That’s how to tell the difference.

Mason bees are in the Megachile family. The are also known as leaf-cutter bees. This mason bee has filled the “pollen baskets” on its hind legs with pollen from the eryngo, and they are now swollen and bright yellow. Pollen is also sticking to the hairs on its thorax and underside. It is a good pollinator!

Carpenter bees and Mason bees are native to our region. Honeybees are not native to the United States. I saw honeybees in the Heritage Garden, but they were not interested in this flower. Honeybees tend to go for sweeter-smelling flowers.

The red admiral, with its characteristic red stripe across the middle of the upper wings, is common in our area.

This tiny gray-blue butterfly is an azure. Some azures are the same blue color as the eryngo flower.

A monarch butterfly also flew overhead while I was taking pictures, but it didn’t stop by. Again, the scent of this flower isn’t attractive to all pollinators.

The squash vine borer larva can be a nuisance in a vegetable garden, but it is a beautiful and beneficial pollinator as an adult moth. Sometimes we have to resist the urge to judge our fellow creature as being good or bad.

The squash vine borer was the flashiest visitor I saw on the flowers.

6. Syrphid flies (hoverflies or flower flies)

When we think of flies, we tend to think of those annoying houseflies or other pests, but there are other kinds of flies. The Syrphidae family, also known as hoverflies or flower flies, feed on pollen and therefore serve as important pollinators for many plants. I found three species of syrphid flies on the eryngo.

Flower flies resemble bees because of their yellow and black striped pattern, but this little insect bears the large eyes and short antennae that are characteristics of a fly. This syrphid is very small, only about a a quarter of an inch long. It looks a lot like the first, but it had a rounder abdomen. The pointed end is an ovipositor, so after inspection, I believe this is the female and the other may be male, so I counted them together.

7. Another kind of syrphid fly

This syrphid fly is a little bigger and fuzzier than the previous one. It could easily be mistaken for a bee.

8. Mystery fly, possibly another syrphid

I was having a difficult time getting good picture of some of these small insects, and as a result, I didn’t get enough details to identify this half-inch-long fly with white triangles on the back of its abdomen.

Houseflies fall into the family of flies known scientifically as Calliphoridae, also called the blowfly family, and they were also represented on our eryngo plant.

One view of this green bottle fly (genus Phormica) shows its iridescent green body. The same green bottle fly can bee seen with its proboscis sipping nectar from the flower in this image.

This is the only image I got of another blowfly species, a cluster fly (genus Pollenia).

Tiger flies prey on carpenter bees, which were feeding on the eryngo flowers, so seeing this predator around the eryngo makes sense.

I could not get a good picture of this one, because it was hiding in the shadows under the flowers. The wing pattern suggests some kind of tiger fly. Its secretive behavior is also a clue to its identity.

The wasps I observed were far too busy collecting nectar and pollen to notice me. I had no concerns about being stung.

Vespid wasps are a large family of wasps that include paper wasps—those insects that make the big paper nests. These insects live in colonies and they do sting when they feel threatened.

I watched a few ants appear very determined as they walked up the stems of the eryngo, dipped their heads into the flower centers, and went back down the stem as swiftly as they arrived.

The ants must have a colony living in the ground under the Eryngo.

Where there are a lot of flying insects, there are going to be some predators. There were damselflies hovering over the blossoms, feeding on the flies, not the flower.

Damselflies are difficult to identify without getting a really good closeup of their abdomens and markings—and my picture wasn’t good enough. I believe this is some kind of spreadwing.

Assassin bugs fall into the category of insects known as “true bugs.” I saw few assassin bugs lurking around the eryngo flowers.

Assassin bugs and their kin have piercing mouth parts that penetrate their prey and suck the juices out. This guy wasn’t there to feed on nectar or pollen.

Like the damselfly and assassin bug, this spider is hanging out somewhere under the flowers to prey on the flies, bees, and other insects that happen into its web.

Spiders tend to set their traps and hide. I never saw the spider that made this tangle-web but I suspect it was well fed.

In total, I found two kinds of bees, two butterflies, one moth, six flies, one wasp, one ant, one damselfly, one assassin bug, and one spider—sixteen different bugs on this one bright, smelly plant!

The take-away from my experience is that scent is a really successful strategy for attracting pollinators. Like the titan arum, the Moroccan mountain eryngo produced a super potent blast of odor for a brief period time and then moved on to the next phase in its life cycle, which suggests that it requires a lot of a plant’s energy reserves, and may not be sustainable for a long time. This strategy works well as long as the timing of the bloom coincides with the pollinators’ need to feed and ability to get to the flowers.

I find this phenomenon fascinating. If you share my passion for plants and their relationships with insects, check out Budburst at budburst.org and find out how you can help scientists who need your observations to contribute data to their research.

©2018 Chicago Botanic Garden and my.chicagobotanic.org


Results

Spatial separation of flowers and traps

The three Drosera species selected for this study differed with regard to their arrangement of flowers and traps (Fig. 1), with each species having significant differences in the spatial separation between flowers and traps (ANOVA, F2,42 = 23.8, P < 0.001). The flower-trap separation in D. spatulata was the greatest followed by D. arcturi and D. auriculata, respectively (Fig. 2).

Flower trap arrangement in Drosera spatulata (A), Drosera arcturi (B) and Drosera auriculata (C). Scale bar = 1 cm.

Mean (±SE) distance in cm (N = 15) of spatial separation between flowers and traps in the three sundew species.

Columns labelled with different letters are significantly different (P < 0.001). Pie chart is percentage of flower visitors (blue) of the total number of insects found on traps in the three sundew species.

Flower visitors and prey insects

Only Diptera (flies) of the families Syrphidae (hover flies), Tachinidae (tachinid flies) and Muscidae (house flies) were common flower visitors and pollinators of the three carnivorous plants. Syrphidae were the most frequent visitors to flowers of D. spatulata, D. arcturi and D. auriculata, comprising 69%, 72% and 76%, respectively, of the total number of Diptera (N = 71, 104 and 83) observed on flowers. Tachinidae and Muscidae represented 25% and 6% of the total number of flower visitors for D. spatulata, respectively, 14% and 8% for D. arcturi and 14% and 10% for D. auriculata. Flower visitors of the three fly families represented 100% (N = 71), 94% (N = 104) and 100% (N = 83) of all insects found on flowers in the three carnivorous species, respectively. Of insects caught by carnivorous traps, there were proportionately few flower visitors of the three fly families representing only 3.8% (N = 183), 4.3% (N = 578) and 3.3% (N = 701) for the three plant species, respectively (Fig. 2). Of the total number of prey (N = 183) found on traps, Hemiptera (bugs), Hymenoptera (wasps/ants) and Coleoptera (beetles) were the most common orders on D. spatulata, representing 24%, 19% and 18%, respectively. Other prey orders included Diptera, Lepidoptera (moths) and Thysanoptera (thrips). Diptera and Coleoptera were the most common prey trapped by D. arcturi representing 40% and 23% of the total number (N = 578), respectively. Other prey of D. arcturi included Lepidoptera, Hemiptera and Thysanoptera. In D. auriculata traps, Diptera were the most common prey representing 48% of the total (N = 701). On D. auriculata traps, Sciaridae (dark-winged fungus gnats), Chironomidae (midges) and Culicidae (mosquitoes) were the major dipteran families, representing 61% of total Diptera (N = 335). Hemiptera was the second major group representing 16% of the total number of prey found on D. auriculata traps. Less common prey orders included Lepidoptera, Trichoptera (caddisflies), Coleoptera, Hymenoptera and Thysanoptera.

Escape of flower visitors from traps

Of the 30 dipteran flower visitors placed onto traps of each plant species, 13% (5–30% for 95% B.C.L.), 7% (2–21%) and 20% (9.5–37%) managed to escape the traps of D. spatulata, D. arcturi and D. auriculata, respectively. No significant differences were observed in the rates of escape among the three plant species (P = 0.32, Chi-square).

Floral and trap volatiles

Analysis of the headspace of the flowers and traps of D. spatulata, D. arcturi and D. auriculata indicated that flowers and traps of D. spatulata and D. arcturi are scentless, while flowers and traps of D. auriculata release odours. We detected eight compounds in the floral headspace collection and four compounds in the trap headspace collection from D. auriculata (Table 1). There were no compounds in common between its flowers and traps with each tissue having a unique odour of specific volatiles. 2′-aminoacetophenone (34% of total volatiles) and 2-phenylethanol (30%) were the most abundant scent compounds detected from the flowers, while plumbagin (74.4%) was the dominant compound in the headspace collected from traps of D. auriculata (Table 1). Minor constituents (2–14%) in the floral headspace included (+/−)-α-pinene, benzaldehyde, (−)-β-pinene, (+/−)-limonene, benzyl alcohol and phenylacetaldehyde. In contrast, minor constituents (5–15%) in the headspace of traps included linalool, geranyl acetone and (E)-β-farnesene.

Colour preferences of flower visitors and other insects

Visual cues significantly affected preference of the flower visitors to different coloured discs (Fig. 3, two-way ANOVA, F5,20 = 7.85, P < 0.001). A significantly higher number of flower visitors was attracted to white discs than to red, black and transparent (P < 0.05, Fig. 3). There were no significant differences between the numbers of flower visitors attracted to yellow, green, red, black or transparent discs (Fig. 3). Visual cues did not affect colour preference of the non-flower-visiting insects (two-way ANOVA, F5,20 = 0.68, P = 0.64).

Attraction of flower-visiting insects and other insects to sticky discs of various colours.

Bars of either flower visitors or other insects designated with different letters were significantly different (P < 0.05).

Spatial separation and visual cues in resolving pollinator-prey conflict in D. spatulata and D. arcturi

When the red and white discs were presented side by side, the 28 flower visitors were distributed not significantly different from an equal ratio as tested with the exact binomial test (EBT, P = 0.34) with 61% caught on white discs compared with 39% on red discs (Fig. 4A). However, increasing the distance between the red and white discs to 5 cm resulted in 82% of those attracted (N = 34) being caught by the white disc, while further increasing the distance to 10 cm gave 91% landing (N = 34) on the white disc compared to the red disc (P < 0.001 and P < 0.001, respectively Fig. 4B,C). On the other hand, non-flower-visiting insects showed no preference for red or white discs when both discs were presented next to each other, or separated vertically by either 5 or 10 cm (Fig. 4A–C).

Trapping flower-visiting insects and other insects on red and white sticky discs mounted next to each other in various arrangements.

(A) Both discs were presented next to each other, (B) separated by 5 cm and (C) separated 10 cm. Letters above bars indicate significant differences at 5% level (Exact binomial test).

Odour in resolving pollinator-prey conflict in D. auriculata

Significantly more flower visitors were attracted to clear sticky surfaces baited with floral odour compared to the same surfaces baited with trap odour or both floral and trap odour (Fig. 5, two-way ANOVA, F3,12 = 29.4, P < 0.001). Thus, trap odour reduces the attraction of flower visitors to floral odour (Fig. 5). A few flower visitors were attracted to clear surfaces baited with trap odour, but this was not significantly different from the control without odour. Significantly larger numbers of other (non-pollinating) insects were captured on clear surfaces baited with floral and trap odour than on traps with either floral or trap odour alone. Trap odour released from clear surfaces captured significantly more other insects than surfaces with floral odour and traps without odour (Fig. 5, two-way ANOVA, F3,12 = 41.5, P < 0.001).

Attraction of flower-visiting insects and other insects to clear sticky cylinder baited with trap odour, floral odour, both floral and trap odour and no odour.

Letters indicate significant differences between means of treatments for other insects or flower visitors at 5% level.

Colour and odour in resolving pollinator-prey conflict in D. auriculata

Flower visitors (N = 18) showed no preference for green or pink colour when the two colours were presented side by side and without odour (Fig. 6A, P = 0.81, EBT). In the same experiment, insects other than flower visitors (N = 51) showed no preference for the green or pink colour (P = 0.58). The addition of the floral odour to the pink discs and the trap odour to green discs resulted in an increase in the number of flower visitors attracted to the pink discs and a reduction in the number of flower visitors attracted to the adjacent green discs (Fig. 6B, N = 32, P < 0.001). In addition, the number of other insects attracted to green discs releasing trap odour was similar to those attracted to pink discs with floral odour (N = 92, P = 0.60). Only three flower visitors landed on the clear discs without odour. Forty-four other insects landed on the two clear discs without odour and there was no preference for either disc (Fig. 6C, P = 0.29). The number of flower visitors attracted to clear discs with floral odour was significantly higher than the number of flower visitors attracted to clear discs with trap odour (Fig. 6D, N = 15, P = 0.01). Similar numbers of other insects were attracted to clear discs with floral odour and to clear discs with trap odour (Fig. 6D, N = 77, P = 0.17). The total number of flower visitors attracted to the green/pink discs with odour was significantly higher than the total number of flower visitors attracted to the green/pink discs without odour (Fig. 6A,B, N = 50, P = 0.05). More flower visitors were attracted to clear discs with odour than to clear discs without odour (Fig. 6C,D, N = 18, P = 0.01). The total number of flower visitors attracted to green/pink discs without odour was significantly higher than the flower visitors attracted to clear discs without odour (Fig. 6A,C, N = 21, P = 0.002). The total number of other insects attracted to the green/pink discs with odour was significantly higher than the number of other insects attracted to the green/pink discs without odour (Fig. 6A,B, N = 143, P < 0.001). A higher number of other insects were attracted to clear discs with odour than the number of other insects attracted to the clear discs without odour (Fig. 6C,D, N = 121, P = 0.003). There was no significant difference in the number of other insects attracted to green/pink discs without odour than to clear discs without odour (Fig. 6A,C, N = 95, P = 0.53).

Trapping flower-visiting insects and other insects on green and pink sticky discs mounted next to each other with floral and trap odour in various arrangements.


The structure of flower visitor networks in relation to pollination across an agricultural to urban gradient

Appendix S1. Study area, land cover, local scale factors, summary statistics and output tables from SEM.

Fig. S2. Relationships between land use and observed and relative linkage density and generality.

Table S1. Coordinates of field sites and land use index.

Table S2. Plant richness per site and mean percentage (%) of bare soil per quadrat.

Table S3. Mean percentage of each land cover type across sites.

Table S4. Relationship between flying insect community and landscape diversity.

Table S5. Summary results of Mantel tests.

Table S6. Relationship between network size, interactions, links and network metrics.

Table S7. Overall characteristics and estimated parameters of flower visitor networks.

Table S8. Number of visits per pollinator morphogroup recorded on our experimental plants.

Table S9. Table of path coefficients, squared multiple correlations and indirect effects from the best-fit SEM.

Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.


Tropical fruit production depends on wild insect communities: bees and lychees in Thailand

The importance of wild insects as pollinators of tropical tree crops has rarely been tested. Across 18 small-scale lychee orchards in northern Thailand, we evaluated the roles of different wild insects as pollinators and predators of pests in fruit production. Quantitative assessments showed that bees (Family Apidae) were strongly dominant (83%) among insect flower visitors, comprising four species in tribes Apini and four in Meliponini. Experimental manipulations of inflorescences showed that fruit production in these orchards was: (1) dependent on flower visits by wild insects because enclosure of inflorescences in mesh bags decreased fruit set (to one-fifth) and (2) not greatly limited by pollinator deficiencies, because hand pollination of unbagged flowers did not enhance fruit set. Pollination success, as indicated by the proportion of unmanipulated flowers setting fruit, correlated positively across orchards with the abundance of large-bodied Apidae (>7 mm most were Apis species) and of Apini, and negatively with abundance of small-bodied Apidae and of all Meliponini, despite the latter being the commonest flower visitors. We conclude that larger-bodied bees are most likely to travel sufficiently far to import genetically diverse pollen, in this landscape-scale mosaic where non-orchard habitats (both agriculture and treed patches) were sufficient to sustain wild pollinators.


Discussion

Role of Pollinators in Mango Fruit Set

A mango tree produces masses of flowers as a survival mechanism to ensure successful production of seeds for perpetuation of the species. Hermaphrodite and male mango flowers are borne within a single inflorescence and their ratio is mainly cultivar related ( Usman et al. 2001 ). Environmental and cultural factors may contribute to variations in flower components to a certain extent ( Bally et al. 2009 ). In various cultivars, flowers reach full bloom in 25–30 days after initiation. Differences in flower or fruit abortion may lead to large variation in yields among mango cultivars.

Nor Hazlina et al. (2008) reported that the ratio of perfect flower to the male mango flower was as high as 1–75. However, in this study a much lower ratio of 1:5 was recorded for Chok Anan and 1:10 for Sala. In spite of this, low fruit set and high dropping off of perfect flowers in both cultivars hampered high mango production in this orchard.

Based on the number of perfect flowers, each mango panicle can bear up to 500 fruits. Although extremely low percentage (0.1–0.25%) of hermaphrodite flowers developed into fruits in some self-pollinated mango cultivars ( Chapman 1964 , Jabatan Pertanian Malaysia 2009 ), more flowers were fertilized in this study and higher percentages of fruit set by naturally pollinated Chok Anan (3.1%) and Sala (4.8%) flowers were recorded. Other flowers were unfertilized, shed off, or failed to set fruits. Progressive thinning of fruits which occurs during their development to maturity ( Bally et al. 2009 ) further reduces high production potential of Malaysian mango ( Azhar and Ithnin 2009 ).

Chok Anan flowers failed to produce fruit set in the covered treatment and hence were strongly pollinator dependent. In the presence of pollinators, Chok Anan is capable to bear fruits in the rainy season which is unusual for other mango clones ( Nor Hazlina et al. 2008 ). The result of this study also showed that Chok Anan has a high pollinator efficiency of 0.711. Therefore, increase in pollinator abundance would certainly amplify its productivity.

Hand pollination has effectively fertilized a considerable amount of flowers. Azhar and Ithnin (2009) successfully produced 26.7% fruit set from 1000 Chok Anan flowers that they hand pollinated. In this study, more than 100% increase in fruit set was recorded for Sala compared with naturally pollinated flowers. In Chok Anan, fruit set production increased about 33%. Eardley et al. (2006) and Ya et al. (2004) also reported large increase in yields of hand pollinated oil palm and pear respectively.

Although a lot of hermaphrodite flowers were hand pollinated in the second treatment, the resultant fruit set were far smaller than the number of pollinated flowers. Unsuccessful delivery of male gamete to the ovule might be the case in Chok Anan because Ding and Khairul Bariah (2013) have discovered that the style of its hermaphrodite flower was longer than the filament of the stamen. Physiological incompatibility has been the main problem for hand pollinated flowers. Mango flowers are usually self-compatible but varying degree of self incompatibility may result from environmental changes. Previously Mukherjee et al. (1968) and Singh et al. (1962) also discovered self-incompatibility in Indian mango. Other mango cultivars like Dashehari, Langra, and Chausa are also found to be self-incompatible ( Sharma and Singh 1970 ).

Apart from poor fruit set, hand pollinating mango flowers is a difficult task because of very small flower size. The flower stigma is easily damaged during the pollen transfer despite exercising extra care. In addition, heavy rain washes off pollen and thus prevents fruit set for most crops ( Nakasone and Paull 1998 ). Coincidently, our study orchard is located in the Northern Peninsular Malaysia which receives very little rain between December and March ( Mohtar et al. 2014 ).

The results of our study emphasized the need for supplementary pollination for a better mango fruit production Malaysian orchard. Our findings also highlighted the importance of various wild pollinators that contributed ∼53% of estimated maximum fruit production. Therefore, there was an urgent need for pollination service to ascertain better fruit production particularly for Chok Anan and Sala mangoes in Malaysia ( Usman et al. 2001 , Sung et al. 2006 ). Furthermore, several reports have confirmed increased fruit/seed set and better quality fruits produced by crops that receive multiple pollinator visits ( Free 1993 , FAO 2008).

Visitation Frequency

Usually insect pollinators have different foraging behavior that may influence pollinator efficiency ( Ne’eman et al. 2010 ). Among the flower visitors observed in this study, Chrysomya displayed higher visitation frequencies and visited more flowers within the allotted time. High visitation frequency may increase the chances of pollen delivery thus increases the chance that a flower matures into a fruit ( Mitchell and Waser 1992 ). In contrary, Mayfield et al. (2001) suggested that pollinator with lesser frequency of visit deposited more pollen on the stigmas. Likewise insects with slow foraging rates (therefore low visitation frequency) can ensure more pollen transfer than those with high foraging rates ( Ivey et al. 2003 ). Longer foraging times may translate into greater pollen removal and more pollen deposition on stigmas ( Horsburgh et al. 2011 ). Two fly genera, Stomorhina and Sarcophaga , certainly had low visitation frequencies on mango flowers thus they were valuable pollinators. However, Sarcophaga flies spent more time grooming their bodies on flower branches instead of spending more time on flowers.

Ants, particularly Camponotus and Iridomyrmex , were also active flower visitors in this orchard despite no record of ant pollinating crops in Malaysia ( Bakhtiar and Maryati 2009 ). From observation on their behavior, ants contributed very little to pollination of mango flowers. They moved actively on mango panicles to search for honey dew secreted by homopteran pests instead of flower nectar. In this study, Camponotus and Iridomyrmex ants had relatively high visitation frequency. Gomez et al. (1996) suggested that the role of ants as pollinators depends heavily on their high relative abundance. Ant pollination becomes evident when they outnumber other floral visitors. Unfortunately, ants are poor pollinators and can also disrupt pollination by deterring other flower visitors, or by stealing nectar ( Corlett 2004 , Ballantyne and Willmer 2012 ).

Deposition of Pollen Grains as Estimator of Pollinator Effectiveness

Pollen carrying capacity varies among pollinator species. In this study, a small parasitic sweet bee, Specodes (Halictidae) had the highest pollen load on its body. Bees are known to be effective pollinators compared with other insect pollinators. They spent relatively long time on the flowers and their hairy bodies make excellent contact with the female flower parts ( Mayfield et al. 2001 ). Comparing with dipteran pollinators, bees, and many other hymenopterans carried a significantly higher proportion of pollen on their bodies ( Howlett et al. 2011 , Rader et al . 2011 , Abrol 2012 ).

Among the dipteran pollinators, Eristalinus carried the highest amount of pollen on its body. Another fly, a small size Stomorhina, also carried relatively large amount of pollen and was frequently observed on mango flowers. Stomorhina is an active pollinator and besides mango it has been reported to pollinate other plants including Tectona grandis in Thailand and tuckeroo ( Cupaniopsis anacardioides : Sapindaceae) in Australia ( Hawkeswood 1983 , Tangmitcharoen and Owens 1997 ). Chrysomya (fly) also displayed high capability to carry mango pollen on its body suggesting its potential as a good mango pollinator. One of its species, C. megacephala carried more avocado pollen than other pollinators in Mexico ( Perez-Balam et al. 2012 ). We found that the sex of the pollinator was not a contributing factor to pollen carrying capacity. Although Stomorhina and Eristalinus females had slightly more pollen on their bodies, the sex difference was not statistically significant. Borkent and Schlinger (2008) also reported no variation in pollen carrying capacity between male and female Eulonchus tristis (Diptera: Acroderidae).

Our study confirmed a considerable involvement of Camponotus ant in mango pollination. This ant also pollinates Mediterranean shrubs Retama sphaerocarpa, Frankenia thymifolia ( Gomez et al. 1996 ), Jatropha curcas ( Luo et al. 2012 ), and plants in the family Euphorbiaceae ( Reddi and Reddi 1984 , Schurch et al. 2000 ). Unlike Camponotus ant, we found that Iridomyrmex ant did not carry any mango pollen on its body. A hard-bodied Iridomyrmex may have difficulty to come in contact with flower anthers thus reduced its chances to contact with the pollens ( Armstrong 1979 ). The lack of bristle on its smooth integument makes it unsuitable to carry mango pollen ( Corlett 2004 ). However, Iridomyrmex anceps was reported by Luo et al. (2012) to be a pollinator of J. curcas in China.

Influenced of Body Size of Pollinator on Pollen Carrying Capacities

According to Pearce et al. (2012) and Luo et al . (2012) , large pollen load was common in large, long, and more robust insect bodies. O’Neill and O’Neill (2010) also reported that the body size of female leaf cutting bee, Megachile rotundata (Hymenoptera: Megachilidae), was positively correlated with the pollen loads it carries. Paralleled to the previous findings, the result of this study showed that a pollinator with big head (head width) and long body carried more pollen than a small-headed and short-bodied pollinator. A relatively big Eristalinus (Syrphidae: Diptera) collected the highest number of pollen and a large Camponotus ant also carried a lot of mango pollen.

The behavior of the pollinators may also influence their pollen carrying capacity. We observed that Sarcophaga flies actively groomed its body after each flower visit. According to Castellanos et al. (2003) , intensive grooming is a way to regulate the amount of pollens from a donor flower to be deposited onto a receiver flower. The Specodes bees typically feed on pollen and nectar thus collect high amount of pollen on their bodies ( Abrol 2012 ). In addition to feeding behavior, pollination efficiency was also influenced by anatomical features of the pollinators ( Larson et al. 2001 ).

As a conclusion, this study highlighted the importance of pollinators in Malaysian mango industry. Self-pollinated and naturally pollinated flowers resulted in very low fruit yield. Some of the mango cultivars such as Chok Anan were completely dependent on insect pollination. Enhancing population of wild pollinators such as Eristalinus , Chrysomya , Stomorhina , Sarcophaga , and Camponotus especially those with big size and hairy body may result in improve pollination service in this mango orchard.


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