Plecoptera

 Perlopsis filicornis, from Zhuzhgova et al. (2015).

Belongs within: Polyneoptera.
Contains: Grypopterygomorpha, Arctoperlaria.

The Plecoptera, stoneflies, are a group of mostly detritivorous or omnivorous insects with nymphs that are mostly aquatic or, if terrestrial, found in damp habitats. Nymphs respire through often finger-like gills that vary between families in their location on the body. Stoneflies are first known in the fossil record from the latest Early Permian (Sinitshenkova 2002a) where they are represented by such species as the slender-bodied, long-legged Perlopsis filicornis. The Palaeonemouridae were a dominant family in the Permian period known from Eurasia and Antarctica (Sinitshenkova 2002a).

The stoneflies: old or new?
Published 23 July 2012
Little snowfly Capnia nana, from here.

Despite being a working entomologist, I have to confess that there are some insect groups with which I am not entirely familiar. The stoneflies, Plecoptera, are one of those groups. I work in arid northern Australia, but stoneflies are associated with cool waters. The highest diversity live in temperate regions of the world; those whose ranges extend into lower latitudes are found higher in the mountains, away from the heat.

Stoneflies live in their favoured waterways as nymphs, emerging when they develop to adulthood (at least one species, Capnia lacustra of Lake Tahoe, appears to also be aquatic as an adult). The adults are large, long-bodied insects that are often better runners than they are fliers. Nymphs are primarily detritivores, but many species are carnivorous to a greater or lesser extent. Adults of some species do not feed; others feed on such things as encrusting algae or lichen or rotten wood. Depending on species, adult stoneflies may have full-sized wings, reduced wings or no wings at all; in some species, both flying and flightless morphs may be present. Two European species, Perla bipunctata and Perlodes microcephala, are solely brachypterous in Britain but may be either brachypterous or macropterous elsewhere in their range (Hynes 1976). Winged females of many species lay eggs while in flight, either dropping them into water or gliding to the water surface and letting the eggs be washed off from the end of the abdomen. Other species attach their eggs to stones underwater or insert them into crevices or rotting wood.

Tasmanian stonefly, Eusthenia sp., photographed by Nuytsia@Tas. More colourful than most other stoneflies, Eusthenia species raise their forewings when threatened to reveal brightly patterned hindwings.

Most recent authors have supported a division of the stoneflies between two lineages, the Antarctoperlaria and Arctoperlaria, that are both morphologically and geographically distinct (Zwick 2000). The Antarctoperlaria are found in South America, Australia and New Zealand. The Arctoperlaria, in contrast, are primarily found in the Northern Hemisphere (except for members of two families, the Perlidae and Notonemouridae). Many species of the Arctoperlaria signal to potential mates by drumming the abdomen on a substrate, a behaviour unknown in the Antarctoperlaria.

Nymph of Acroneuria abnormis, photographed by Michel Gauvin.

Stoneflies have often been regarded as one of the most primitive groups of winged insects, and their position remains contentious. The two main theories are that they are the sister group to all other neopteran insects (insects that are capable of folding the wings back flat over the body), or that they belong to the group known as Polyneoptera that also includes grasshoppers and cockroaches. Which of these is correct has been regarded as potentially significant in understanding how flight evolved in insects as a whole. It has been suggested that insect wings are homologous with articulated gills in aquatic nymphs. As well as Plecoptera, the two living non-neopteran insect orders Odonata (dragonflies) and Ephemeroptera (mayflies) are aquatic as nymphs, and if Plecoptera are basal to other neopterans then it suggests that this life history may be ancestral for winged insects as a whole. However, differences in nymphal morphology between the three groups may indicate that the aquatic lifestyle has been independently acquired in all three from terrestrial ancestors, which would also be more likely if stoneflies are derived polyneopterans. Molecular studies have supported a polyneopteran relationship for stoneflies, but not with rock-solid support (e.g. Terry & Whiting 2005); morphological studies are equivocal and do not clearly point either way (Zwick 2009). The fossil record is also unclear: while a number of early insect groups have been connected to stoneflies, whether they are true stem-Plecoptera or closer to other polyneopteran lineages is debatable (Béthoux et al. 2011). It is also worth pointing out that while similarities between stonefly and mayfly gills have been cited in relation to their supposed homology with wings, different families of stoneflies have different gill types, and we still do not know whether and what kind of gills were ancestral for Plecoptera. Also, in those stoneflies with plate-like gills, the gills are not articulated like wings and incapable of independent movement (Zwick 2009).

Systematics of Plecoptera

Characters (from Sinitshenkova 2002a): Body size moderately small to large. Head prognathous, with mouthparts chewing (mandibles sometimes much reduced). Thorax structure little modified, prothorax large, lacking wide paranota, meso- and metathoraces of similar structure. Legs cursory (with swimming hairs in many nymphs), with tarsus 3-segmented. Wings membranous, almost completely overlapping each other over abdomen at rest, with pre-anal venation similar in both pairs, excluding RS which lost its base and originated from M in hind wing (nymphal wing pad with RS base preserved), and CuA which is usually (primarily) simple in hind wing; hind wing anal area usually large. Wing venation not especially rich, with main veins branching at or beyond wing midlength, more often forked, RS and CuA up to 4 or 5 branches (in ground plan CuA is similar to M in having 2 branches only). Cross veins not numerous besides 2 characteristic rows aligned CuA, with most constant r-rs and r-m near RS and M forkings (roughly at level of SC apex). RS typically and probably plesiomorphically originating near wing base and running parallel to R. Flight functionally four-winged, in-phase. mainly anteromotoric in spite hind wing widened basally. Abdomen with full number of segments, lacking paranota. Primary ovipositor lost. Cerci always present, usually long, multisegmented, rarely one-segmented in adult. Nymphs aquatic, now populating almost exclusively running or cold water, often bearing external gills of different structure and disposition.

<==Plecoptera [Filipalpia, Leptoperloidea, Perlariae, Perlida, Perlina, Perlopseina]
    |--PalaeoperlaRJ93 [PalaeoperlidaeGE05]
    |    `--P. exactaRJ93
    |--PerlopsisS02a [PerlopseidaeGE05]
    |    `--P. filicornisS02a
    |--+--GrypopterygomorphaGE05
    |  `--ArctoperlariaGE05
    `--PalaeonemouridaeGE05
         |--OhionymphaS02b
         |--Uralonympha varicaRJ93
         `--Palaeonemoura claraRJ93
Plecoptera incertae sedis:
  Plutopteryx beataS02b
  EcdyoperlaS02a
  TriassoperlaS02b
  BerekiaS02b
  PerlitodesS02b
  SavinaS02b
  UroperlaS02b
  Paraperla frontalisB86
  IsocapniaB86
  SharaperlaS02c
  BestioperliscaS02c
  MongolonemouraS02c
  Megateptoperla grandisO81
  PerliscaS02b
  PerlomimusS02b
  TrianguliperlaS02b
  Acroneuria californicaR00
  Clioperla clioN96
  Megandiperla kuscheliRD77
  SemblisR26
    |--S. linneanaR26
    `--S. nebulosaR26

*Type species of generic name indicated

References

Béthoux, O., Y. Cui, B. Kondratieff, B. Stark & D. Ren. 2011. At last, a Pennsylvanian stem-stonefly (Plecoptera) discovered. BMC Evolutionary Biology 11: 248.

[B86] Botosaneanu, L. 1986. Insecta: Plecoptera, Trichoptera. In: Botosaneanu, L. (ed.) Stygofauna Mundi: A Faunistic, Distributional, and Ecological Synthesis of the World Fauna inhabiting Subterranean Waters (including the Marine Interstitial) p. 619. E. J. Brill/Dr W. Backhuys: Leiden.

[GE05] Grimaldi, D., & M. S. Engel. 2005. Evolution of the Insects. Cambridge University Press: New York.

Hynes, H. B. N. 1976. Biology of Plecoptera. Annual Review of Entomology 21: 135–153.

[N96] Nelson, C. H. 1996. Placement of Helopicus rickeri Stark in Hydroperla Frison (Plecoptera: Perlodidae) with the description of the adult female, nymph, and egg and a cladistic analysis of Hydroperla. Proceedings of the Entomological Society of Washington 98 (2): 237–244.

[O81] O’Brien, C. O. 1981. A. A. Book of New Zealand Wildlife: A guide to the native and introduced animals of New Zealand. Lansdowne Press: Auckland.

[RD77] Richards, O. W., & R. G. Davies. 1977. Imms’ General Textbook of Entomology 10th ed. vol. 2. Classification and Biology. Chapman and Hall: London.

[R26] Risso, A. 1826. Histoire naturelle des principales productions de l’Europe méridionale et particulièrement de celles des environs de Nice et des Alpes maritimes vol. 5. F.-G. Levrault: Paris.

[R00] Ross, E. S. 2000. Embia: Contributions to the biosystematics of the insect order Embiidina. Occasional Papers of the California Academy of Sciences 149: 1–53, 1–36.

[RJ93] Ross, A. J., & E. A. Jarzembowski. 1993. Arthropoda (Hexapoda; Insecta). In: Benton, M. J. (ed.) The Fossil Record 2 pp. 363–426. Chapman & Hall: London.

[S02a] Sinitshenkova, N. D. 2002a. Order Perlida Latreille, 1810. The stoneflies (=Plecoptera Burmeister, 1839). In: Rasnitsyn, A. P., & D. L. J. Quicke (eds) History of Insects pp. 281–287. Kluwer Academic Publishers: Dordrecht.

[S02b] Sinitshenkova, N. D. 2002b. Ecological history of the aquatic insects. In: Rasnitsyn, A. P., & D. L. J. Quicke (eds) History of Insects pp. 388–426. Kluwer Academic Publishers: Dordrecht.

[S02c] Sinitshenkova, N. D. 2002c. New late Mesozoic mayflies from the Shar-Teeg locality, Mongolia (Insecta, Ephemerida=Ephemeroptera). Paleontologicheskii Zhurnal 2002 (3): 43–48 (translated: Paleontological Journal 36 (3): 270–276).

Terry, M.D., & M. F. Whiting. 2005. Mantophasmatodea and phylogeny of the lower neopterous insects. Cladistics 21: 240–257.

Zwick, P. 2000. Phylogenetic system and zoogeography of the Plecoptera. Annual Review of Entomology 45: 709–746.

Zwick, P. 2009. The Plecoptera–who are they? The problematic placement of stoneflies in the phylogenetic system of insects. Aquatic Insects 31 (suppl. 1): 181–194.

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