Mecoptera (from the Greek: meco- = "long", -ptera = "wings") are an order of insects with about 550 species in nine families worldwide. Mecoptera are sometimes called scorpionflies after their largest family, Panorpidae, in which the males have enlarged genitals that look similar to the stinger of a scorpion. The Bittacidae, or hangingflies, are a prominent family of elongate insects known for their elaborate mating rituals, in which females choose mates based on the quality of gift prey offered by various males.
While modern Mecoptera are overwhelmingly predators or consumers of dead organisms, early ones might have played an important role before the evolution of other insects in pollinating extinct gymnosperms.
Anatomy and biology
Mecoptera are small to medium insects with slender, elongated, bodies. They have relatively simple mouthparts, with long mandibles and fleshy palps, which resemble those of the more primitive true flies. Like many other insects, they possess compound eyes on the sides of their heads, and three ocelli on the tops. Most Mecoptera feed on vegetation in moist environments; in hotter climates, they may therefore be active only for short periods of the year.
The wings are narrow in shape, with numerous cross-veins, and somewhat resemble those of primitive insects such as mayflies. A few genera, however, have reduced wings, or have lost them altogether. The abdomen is cylindrical, and typically curves upwards in the male, superficially resembling the tail of a scorpion, the tip containing an enlarged structure called the genital bulb.
The female lays the eggs in close contact with moisture, and the eggs typically absorb water and increase in size after deposition. In species that live in hot conditions, the eggs may not hatch for several months, the larvae only emerging when the dry season has finished. More typically, however, they hatch after a relatively short period of time.
The larvae are usually quite caterpillar-like, with short, clawed, true legs, and a number of abdominal prolegs. They have sclerotised heads with compound eyes and mandibulate mouthparts. The tenth abdominal segment bears either a suction disc, or, less commonly, a pair of hooks. They generally eat vegetation or scavenge for dead insects, although some predatory larvae are known.
The larva crawls into the soil or decaying wood to pupate, and does not spin a cocoon. The pupae are exarate, meaning the limbs are free of the body, and are able to move their mandibles, but are otherwise entirely nonmotile. In drier environments, they may spend several months in diapause, before emerging as adults once the conditions are more suitable.
Evolution
DNA evidence indicates fleas, which are traditionally considered a separate order (Siphonaptera), are instead highly specialized Mecoptera. Some morphological evidence exists for the grouping of Siphonaptera and Mecoptera Boreidae. Two synapomorphies are the production of resilin, a very flexible and springy type of cuticle, and a reversion to panoistic ovarioles. If grouped with the fleas, Mecoptera would have about 3000 known species.
Mecoptera have special importance in evolution of Insecta. Two of the most important insect orders, Lepidoptera and Diptera, along with Trichoptera, probably evolved from ancestors belonging to, or strictly related to, the Mecoptera. This is apparent from anatomical and biochemical similarities, but, moreover, transitional fossils, such as Permotanyderus and Choristotanyderus, have been discovered to lie between the Mecoptera and Diptera.
The group was once much more widespread and diverse than at present, having as many as four suborders during the Mesozoic.
First pollinators
Extinct Mecoptera species have been proposed to have been important plant pollinators. Early nonangiosperm gymnosperm seed plants during the late Middle Jurassic to midâ€"Early Cretaceous period have been believed to be mainly wind-pollinated. However, examination of fossil mecopterans show they had siphon feeding apparatus that could fertilize early gymnosperms by feeding on their nectar and pollen. The lack of iron enrichment in their fossilized probosces rules out a use in blood drinking. One question over this suggestion is that so far pollen has not been found associated with these feeding parts, which is surprising for the amber-encased insects which should have preserved pollen, but "further fossils may provide this information".
Eleven species have been identified belonged to three families, Mesopsychidae, Aneuretopsychidae, and Pseudopolycentropodidae for which "the encompassing name Aneuretopsychina is available". Their lengths range from 3Â mm in Parapolycentropus burmiticus to 28Â mm in Lichnomesopsyche gloriae. The proboscis could be as long as 10Â mm. Pollen transfer has been suggested to occur by body surface transport on mouthparts and head surfaces like that in bee flies and hover flies, but no such associated pollen has been found, though the insects were preserved in amber. They are thought to have pollinated such plants as Caytoniaceae, Cheirolepidiaceae, Czekanowskiaceae, Pentoxylaceae, and Gnetales, as their ovulate organs are either poorly suited for wind pollination or have structures that could support long-proboscid fluid feeding.
Mating
The following is a description by Gullen and Cranston of the mating habits of the Bittacidae:
References
- ^ Byers, G. W. and Thornhill, R. 1983. Biology of the Mecoptera. Annual review of Entomology. 28: 203-228
- ^ a b c Ollerton J. Coulthard E. (2009). Evolution of Animal Pollination. Science, 326: 808-809. doi:10.1126/science.1181154
- ^ a b c d e f Ren D, Labandeira CC, Santiago-Blay JA, Rasnitsyn A, Shih CK, Bashkuev A, Logan MA, Hotton CL, Dilcher D. (2009). Probable Pollination Mode Before Angiosperms: Eurasian, Long-Proboscid Scorpionflies. Science, 326 (5954), 840-847. doi:10.1126/science.1178338
- ^ a b c d e f Hoell, H.V., Doyen, J.T. & Purcell, A.H. (1998). Introduction to Insect Biology and Diversity, 2nd ed. Oxford University Press. pp. 488â€"491. ISBN 0-19-510033-6.Â
- ^ Whiting, Michael F. (2002). "Mecoptera is paraphyletic: multiple genes and phylogeny of Mecoptera and Siphonaptera". Zoologica Scripta 31 (1): 93â€"104. doi:10.1046/j.0300-3256.2001.00095.x.Â
- ^ Gullan, P.J. and P.S. Cranston. The Insects: An Outline of Entomology, second edition. 2000: Blackwell Science, Ltd.
- Grimaldi, D. and Engel, M.S. (2005). Evolution of the Insects. Cambridge University Press. ISBNÂ 0-521-82149-5.Â
- Archibald, S.B. (2005). "New Dinopanorpida (Insecta: Mecoptera) from the Eocene Okanogan Highlands (British Columbia, Canada and Washington State, USA)". Canadian Journal of Earth Sciences 42 (2): 119â€"136. doi:10.1139/e04-073.Â
External links
- Mecoptera at the Tree of Life
- Mecoptera image gallery at myrmecos.net
- Video of Mecoptera from Austria
- Mecoptera in UK on BBC wildlife website (third image in)