Plecoptera is anorder ofinsects, commonly known asstoneflies. Some 3,500 species are described worldwide,[1] with new species still being discovered. Stoneflies are found worldwide, except Antarctica.[2] Stoneflies are believed to be one of the most primitive groups ofNeoptera, with close relatives identified from theCarboniferous and LowerPermian geological periods, while true stoneflies are known from fossils only a bit younger. Their modern diversity, however, apparently is ofMesozoic origin.[3]
Plecoptera are found in both theSouthern andNorthern Hemispheres, and the populations are quite distinct, although theevolutionary evidence suggests species may have crossed theequator on a number of occasions before once again becoming geographically isolated.[3][4]
All species of Plecoptera are intolerant ofwater pollution, and the presence of theirnymphs in a stream or still water is usually an indicator of good or excellent water quality.[5]
Stoneflies have a generalized anatomy, with few specialized features compared to other insects. They have simplemouthparts with chewingmandibles, long, multiple-segmentedantennae, largecompound eyes, and two or threeocelli. The legs are robust, with each ending in two claws. Theabdomen is relatively soft, and may include remnants of the nymphal gills even in the adult. Bothnymphs and adults have long, pairedcerci projecting from the tip of their abdomens.[6]
The name "Plecoptera" literally means "braided-wings", from theAncient Greekplekein (πλέκειν, "to braid") andpteryx (πτέρυξ, "wing").[7] This refers to the complex venation of their two pairs ofwings, which aremembranous and fold flat over their backs. Stoneflies are generally not strong fliers, and some species are entirely wingless.
The nymphs (technically, "naiads") are aquatic and live in thebenthic zone of well-oxygenated lakes and streams. A few species found in New Zealand and nearby islands have terrestrial nymphs, but even these inhabit only very moist environments. The nymphs physically resemble wingless adults, but often have external gills, which may be present on almost any part of the body. Nymphs can acquire oxygen via diffusing through the exoskeleton, or through gills located on behind the head, on the thorax, or around the anus.[10] Due to their nymph's requirement for well oxygenated water, the species is very sensitive to water pollution. This makes them important indicators for water quality.[11] Most species are herbivorous as nymphs, feeding on submerged leaves and benthic algae, but many are hunters of other aquatic arthropods.[6]
The female can lay up to one thousand eggs. It will fly over the water and drop the eggs in the water. It also may hang on a rock or branch. Eggs are covered in a sticky coating which allows them to adhere to rocks without being swept away by swift currents.[12] The eggs typically take two to three weeks to hatch, but some species undergodiapause, with the eggs remaining dormant throughout a dry season, and hatching only when conditions are suitable.[6]
The insects remain in the nymphal form for one to four years, depending on species, and undergo from 12 to 36molts before emerging and becoming terrestrial as adults.[13] Before becoming adults, nymphs will leave the water, attach to a fixed surface and molt one last time.
The adults generally only survive for a few weeks, and emerge only during specific times of the year when resources are optimal. Some do not feed at all, but those that do are herbivorous.[6] Adults are not strong fliers and generally stay near the stream or lake they hatched from.[12]
A summary of the phylogeny of stoneflies is shown below. While the Antarctoperlaria, Arctoperlaria, Euholognatha, Systellognatha are well supported, several further relationships are disputed.[14][15][16] Some families have only been analyzed by one study (indicated by dashed lines) and their placement may change in the near future.
^Romolo Fochetti & José Manuel Tierno de Figueroa (2008) [Originally published inHydrobiologia Vol. 595 in 2008]. "Global diversity of stoneflies (Plecoptera; Insecta) in freshwater". In E. V. Balian; C. Lévêque; H. Segers & K. Martens (eds.).Freshwater Animal Diversity Assessment. Developments in Hydrobiology. Vol. 198. pp. 365–377.doi:10.1007/978-1-4020-8259-7_39.hdl:2067/1437.ISBN978-1-4020-8258-0.
^abcdHoell, H.V.; Doyen, J.T. & Purcell, A.H. (1998).Introduction to Insect Biology and Diversity (2nd ed.). Oxford University Press. pp. 383–386.ISBN978-0-19-510033-4.
^Ding, Shuangmei; Li, Weihai; Wang, Ying; Cameron, Stephen L.; Murányi, Dávid; Yang, Ding (June 2019). "The phylogeny and evolutionary timescale of stoneflies (Insecta: Plecoptera) inferred from mitochondrial genomes".Molecular Phylogenetics and Evolution.135:123–135.Bibcode:2019MolPE.135..123D.doi:10.1016/j.ympev.2019.03.005.PMID30876966.
^South, Eric J.; Skinner, Rachel K.; DeWalt, R. Edward; Kondratieff, Boris C.; Johnson, Kevin P.; Davis, Mark A.; Lee, Jonathan J.; Durfee, Richard S. (January 2021). "Phylogenomics of the North American Plecoptera".Systematic Entomology.46 (1):287–305.Bibcode:2021SysEn..46..287S.doi:10.1111/syen.12462.
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