stonefly

(click to enlarge)
Stonefly (Plecoptera) (credit: William E. Ferguson)

Any of some 1,550 insect species (order Plecoptera) with adults, about 0.25 – 2.5 in. (6 – 60 mm) long, that are generally gray, black, or brown. They have long antennae; weak, chewing mouthparts; and two pairs of membranous wings that, at rest, fold like a fan. The hind wings are generally broader but shorter than the forewings. Despite their well-developed wings, stoneflies are poor fliers. The female drops a mass of up to 6,000 eggs into a stream. Nymphs resemble adults but are wingless and may have external gills; they feed on plants, decaying organic matter, and insects. The nymphal stage lasts one to four years; adults live several weeks.

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(Stoneflies)

Class: Insecta

Order: Plecoptera

Number of families: 16

Evolution and systematics

Stonefly fossils date from the early Permian, about 258 to 263 million years ago. The fossil record of just under 200 species is most diverse in the Jurassic and is considered fragmentary in comparison with other aquatic insects, probably due to stoneflies' preference for running waters that are not conducive to burial and fossilization. Stoneflies comprise a hemimetabolous (i.e., undergoing complete metamorphosis) order divided into two suborders: Arctoperlaria, containing 12 families (Capniidae, Chloroperlidae, Leuctridae, Nemouridae, Notonemouridae, Paltoperlidae, Perlidae, Pteronarcyidae, Scopuridae, Styloperlidae, and Taeniopterygidae); and Antarctoperlaria, containing four families (Austroperlidae, Diamphipnoidae, Eustheniidae, and Gripopterygidae). The order includes five superfamilies and more than 2,000 species.

Physical characteristics

Adult stoneflies vary in body length from about 0.19 to 1.97 in (5 to 50 mm) and in color from brown or black to green or yellow, usually marked with distinctive light or dark patterns. They are typically winged, except, for example, a wingless aquatic adult of the family Capniidae known from the depths of Lake Tahoe, Nevada. Wings are typically fully winged (macropterous), but the wings of one or both sexes of some species or high altitude or latitude populations of a particular species are shortened (brachypterous) and are not functional. The ordinal name (Plecoptera = "folded wings") describes the hind wings that typically have an expanded posterior lobe that folds under the main wing. Adults have 10 abdominal segments, a three-segmented tarsus, and a pair of terminal, usually multisegmented, cerci. The multisegmented larval cerci become reduced to fewer segments in some taxa and to a single segment in males of the families Leuctridae, Nemouridae, and some Taeniopterygidae. Males have distinctive genitalia consisting of various modifications of the ninth and tenth segments into paired hooks, lobes (paraprocts), sclerotized paired stylets, or a median terminal probe (epiproct). The aedeagus is housed inside the abdomen and extruded during copulation from behind the ninth sternum. The external female genitalia consists of a lobe-like plate usually on the eighth abdominal sternum covering the genital opening. Larvae may or may not resemble their adult forms, and those of particular families or genera vary from being gill-less to having simple or branched gills, diagnostically located and structured, arising from parts of the body such as near mouthparts, thorax, coxae, or abdomen. Larvae always have a pair of multisegmented cerci, and the adults of gilled taxa usually retain stubs or vestiges of the larval gills that aid in their identification.

Distribution

This order is distributed worldwide, on all continents except Antarctica, and on most major islands except Cuba, Fiji, Hawaii, and New Caledonia. Species of the suborder Arctoperlaria are generally distributed in the Northern Hemisphere; exceptions are the family Notonemouridae, which occurs only in southern South America, southern Africa, Madagascar, Australia, Tasmania, and New Zealand, and the two genera of the family Perlidae, Anarcroneuria and Neoperla, that have moved south across the Equator in recent times. The suborder Antarctoperlaria is restricted to the Southern Hemisphere.

Habitat

Stoneflies are almost exclusively inhabitants of streams, where their larvae inhabit organic or mineral substrates. Adults occur in streamside microhabitats, including on or under rocks, moss, debris, leaf packs on the bank or projecting above the water surface, and in riparian vegetation. The larvae of a few species occur in wave-swept substrates of cold alpine or boreal lakes or in intermittent streams.

Behavior

The typical mating system of Northern Hemisphere stoneflies involves aggregation of males and females at encounter sites near streams, and vibrational communication for mate finding. Males call for females with species-specific drumming signals while performing a ranging search, and receptive stationary females answer with a simple drumming signal. These signals and the accompanying positioning allow males to minimize their search and triangulate on a particular female. Copulation occurs immediately after location with no specialized display. Males are polygamous, but females mate only once and then will no longer answer male drumming calls.

Feeding ecology and diet

Stonefly adults of particular taxa are either nonfeeders (e.g., members of the group Systellognatha of Arctoperlaria) or are mainly herbivorous, feeding on pollen, nectar, or other plant parts (e.g., some species of the group Euholognatha of Arctoperlaria). Larvae are either primarily herbivoredetritivores, insectivores, or omnivores, and in some cases their diet shifts among these categories as they develop through 10 to 25 instars. Herbivore-detrivores have molari-form mandibles and are either scrapers, grazers, collector-gatherers, shredders, or gougers. Predators have sharp-cusped mandibles and toothed laciniae for grasping and holding their prey, which they actively seek in the interspaces of their leaf-pack or on mineral substrates in streams.

Reproductive biology

The mating of stoneflies involves a male mounting a female, curving his abdomen around her left or right side, engaging and pulling down the subgenital plate with his external genitalia, and typically inserting his aedeagus into her bursa. Sperm is therefore typically conveyed into the female by the intromittent aedeagus, but in some species sperm is deposited in a pocket beneath the subgenital plate and then aspirated internally by the female, while in other species sperm is conveyed through a hollow male epiproct. Eggs vary considerably in size, shape, and chorionic (egg shell) ornamentation and sculpturing. Penetration by sperm through a micropyle and fertilization, as in most insects, is delayed until just before oviposition (laying of eggs). Eggs are deposited in pellets or masses and released in one of two ways: 1) directly into water by the female splashing into the surface or dropping eggs from the air during an oviposition flight; or 2) being washed off in shallow water. Eggs may hatch within three to four weeks or enter a diapause (a period of arrested development) lasting from three months to one or more years. Generation time for larvae varies from four months to three or four years, depending on the taxa and on environmental conditions. The short-lived adults provide no parental care.

Conservation status

Stoneflies generally require unpolluted streams for continued population health and are therefore important biological indicators of stream water quality. They are important components of one of the major biomonitoring measures, the EPT (Ephemeroptera-Plecoptera-Trichoptera) Index. Some species are endemic to particular stream watersheds or rare and restricted in distribution to small geographic regions, and are therefore listed on various regional or national endangered species lists. Stonefly larvae can generally be thought of as similar in relative size, space requirements, and clean water physical and chemical tolerance to trout and other fish juveniles. Management practices of stream fisheries are therefore conducive also to stonefly management, although habitat or species management practices specifically for stoneflies have rarely been proposed or practiced.

The 2002 IUCN Red List includes four stonefly species. Alloperla roberti is categorized as Extinct; Leptoperla cacuminis and Riekoperla darlingtoni as Vulnerable; and Eusthenia nothofagi as Data Deficient.

Significance to humans

Stoneflies are entirely beneficial to humans as integral and important components of stream food webs and biological indicators of good water quality. Most adults have vestigial mouthparts and cannot bite. Their importance as fish food makes them, along with mayflies, caddisflies, and midges, of much interest to fly fishermen.

Species accounts

Resources

Resh, V. H., and D. M. Rosenberg. The Ecology of Aquatic Insects. New York: Praeger Publishers, 1984.

Sinitschenkova, N. D. "Paleontology of Stoneflies." In Ephemeroptera and Plecoptera, edited by Peter Landolt and Michel Sartori. Fribourg, Switzerland: Mauron and Tinguely; Lachat SA, 1995.

Stark, B. P., S. W. Szczytko, and C. R. Nelson. American Stoneflies: A Photographic Guide to the Plecoptera. Columbus, OH: Caddis Press, 1998.

Stewart, K. W. "Vibrational Communication (Drumming) and Mate-searching Behavior of Stoneflies (Plecoptera); Evolutionary Considerations." In Trends in Research in Ephemeroptera and Plecoptera, edited by Eduardo Dominguez. New York: Kluwer Academic/Plenum Publishers, 2001.

Stewart, K. W., and P. P. Harper. "Plecoptera." In An Introduction to the Aquatic Insects of North America, 3rd ed., edited by R. W. Merritt and K. W. Cummins. Dubuque, IA: Kendall/Hunt Publishing, 1996.

Stewart, K. W., and B. P. Stark. Nymphs of North American Stonefly Genera (Plecoptera), 2nd ed. Columbus, OH: Caddis Press, 2002.

Shepard, W. D., and K. W. Stewart. "Comparative Study of Nymphal Gills in North American Stonefly (Plecoptera) Genera and a New, Proposed Paradigm of Plecoptera Gill Evolution." Miscellaneous Publications Entomological Society of America 55 (1983): 1–57.

Stewart, K. W. "Theoretical Considerations of Mate-finding and Other Adult Behaviors of Plecoptera." Aquatic Insects 16 (1993): 95–104. ——. "Vibrational Communication in Insects: Epidomy in the Language of Stoneflies." American Entomologist 43 (1997): 81–91.

Zwick, P. "Phylogenetic System and Zoogeography of the Plecoptera." Annual Review of Entomology 45 (2000): 709–746.

[Article by: Kenneth W. Stewart, PhD]

An order of primitive insects known as the stoneflies. Except for wings and tracheal gills, there are relatively slight differences between aquatic immature stages and adult mature ones. The soft and somewhat flattened body, strong legs, paired tarsal claws, chewing mouthparts, and rusty blacks, dull yellows, and browns are characteristic of both immature and adult stages (see illustration).

Plecoptera. (a) Nymph of Perla, (b) Adult of Pteronarcys. (After A. H. Morgan, Field Book of Ponds and Streams, Putnam, 1930)

Immature stoneflies live in the rapid, stony parts of clean, swift streams, although a few species occur along the rocky shores of large temperate lakes.

Adult stoneflies hold the wings close to the backs when at rest or walking. The hindwings are pleated and hidden. The name Plecoptera means pleated wings.

In various parts of North America stonefly adults emerge in every month of the year. Successions of species reach their peaks of abundance from November to March, with some extending to August. Nymphs and adults of some species are plant feeders; others are carnivorous. See also Insecta.

Stoneflies Fossil range: 299–0 Ma PreЄ Є O S D C P T J K Pg N Permian - Recent
Adult of genus Eusthenia
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Hexapoda
Class:	Insecta
Subclass:	Pterygota
Infraclass:	Neoptera
Superorder:	Exopterygota
Order:	Plecoptera Burmeister, 1839
Suborders
Arctoperlaria and see text

Plecoptera are an order of insects, commonly known as stoneflies. There are some 1,700 recorded species worldwide^{[citation needed]}, and new ones are still being discovered. Stoneflies are believed to be one of the most primitive groups of Neoptera, with close relatives identified from the Carboniferous and Lower Permian geological periods, while true stoneflies are known from fossils only a bit younger. The modern diversity however apparently is of Mesozoic origin.^[1]

Plecoptera are found in both the Southern and Northern hemispheres, and the populations are quite distinct although the evolutionary evidence suggests that species may have crossed the equator on a number of occasions before once again becoming geographically isolated^[2].

All species of Plecoptera are intolerant of water pollution and their presence in a stream or still water is usually an indicator of good or excellent water quality.

Description and ecology

Stonefly nymph

Stonefly adult

Stoneflies have a generalised anatomy, with few specialised features. They have simple mouthparts with chewing mandibles, long, multi-segmented antennae, large compound eyes and two or three ocelli. The legs are robust, with each ending in two claws. The abdomen is relatively soft, and may include remnants of the nymphal gills even in the adult. Both nymphs and adults have long paired cerci projecting from the tip of their abdomens.^[3]

The name "Plecoptera" literally means "braided-wings", from the Ancient Greek plekein (πλέκειν, "to braid") and pteryx (πτέρυξ, "wing")^[4]. This refers to the complex venation of their two pairs of wings, which are membranous and fold flat over the back. Stoneflies are generally not strong fliers, and some species are entirely wingless.

A few wingless species such as the Lake Tahoe Benthic Stonefly ("Capnia" lacustra^[5]) or Baikaloperla are the only known insects that are exclusively aquatic from birth to death^[6]. Some true water bugs (Nepomorpha) may also be fully aquatic for their entire life, but can leave the water to travel.

The females lay hundreds or even thousands of eggs in a ball which they initially carry about on their abdomen, and later deposit into the water. The eggs typically take two to three weeks to hatch, but some species undergo diapause, with the eggs remaining dormant throughout a dry season, and hatching only when conditions are suitable.^[3]

The nymphs are aquatic and live in the benthic 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. In addition, they can also respire through the general body surface, and some even lack gills altogether. Most species are herbivorous as nymphs, feeding on submerged leaves and benthic algae, but many are hunters of other aquatic arthropods.^[3]

The insects remain in the nymphal form for one to four years, depending on species, and undergo anything from 12 to 33 molts before emerging and becoming terrestrial as adults. The adults generally only survive for a few weeks, and emerge only during specific times of the year. Some do not feed at all, but those that do are herbivorous.^[3]

Systematics

Traditionally, the stoneflies were divided into two suborders, the "Antarctoperlaria" (or "Archiperlaria") and the Arctoperlaria. However, the former simply consists of the two basalmost superfamilies of stoneflies, which do not seem to be each other's closest relatives. Thus, the "Antarctoperlaria" are not considered a natural group (despite some claims to the contrary).^[7]

The Arctoperlaria, meanwhile, have been divided into two infraorders, the Euholognatha (or Filipalpia) and the Systellognatha (also called Setipalpia or Subulipalpia). This corresponds to the phylogeny^{[citation needed]}, with one exception: the Scopuridae must be considered a basal family in the Arctoperlaria, not assignable to any of the infraorders. Alternatively, the Scopuridae were placed in an unranked clade "Holognatha" together with the Euholognatha (meaning approximately "advanced Holognatha"). But the Scopuridae do not appear significantly closer to the Euholognatha than to the Systellognatha^{[citation needed]}.

In addition, not adopting the clades Antarctoperlaria and Holognatha allows for a systematic layout of the Plecoptera that adequately reproduces phylogeny, while retaining the traditional ranked taxa.^[8]

Adult of family Taeniopterygidae (Euholognatha)

Adult of family Perlidae (Systellognatha)

Basal lineages ("Antarctoperlaria")

• Superfamily Eusthenioidea
  • Family Diamphipnoidae
  • Family Eustheniidae
• Superfamily Leptoperloidea
  • Family Austroperlidae
  • Family Gripopterygidae

Suborder Arctoperlaria

• Basal family Scopuridae
• Infraorder Euholognatha
  • Family Capniidae (ca. 300 species) - small winter stoneflies
  • Family Leuctridae - rolled-winged stoneflies
  • Family Nemouridae (ca. 400 species) - spring stoneflies
  • Family Notonemouridae
  • Family Taeniopterygidae (ca. 75 species) - winter stoneflies
• Infraorder Systellognatha
  • Family Chloroperlidae (100+ species) - green stoneflies
  • Family Perlidae (ca. 400 species) - common stoneflies
  • Family Perlodidae (250+ species)
  • Family Peltoperlidae (ca. 50 species) - roachlike stoneflies
  • Family Styloperlidae (ca. 7 species)
  • Family Pteronarcyidae (ca. 12 species) - salmonflies, giant stoneflies

Footnotes

1. ^ Zwick (2000)
2. ^ Hynes (1993), Zwick (2000
3. ^ ^{a b c d} Hoell, H.V., Doyen, J.T. & Purcell, A.H. (1998). Introduction to Insect Biology and Diversity, 2nd ed.. Oxford University Press. pp. 383-386. ISBN 0-19-510033-6. 
4. ^ Woodhouse (1910)
5. ^ The genus Capnia is not monophyletic and this species is suspected to belong elsewhere: Nelson (1996a)
6. ^ Holst (2000)
7. ^ Nelson (1996b)
8. ^ Nelson (1996b), Zwick (2000)

References

Wikimedia Commons has media related to: Plecoptera

• Holst, E.M. (2000): Lake Tahoe benthic stonefly (Capnia lacustra). In: Murhy, D.D. & Knopp, C.M.: Lake Tahoe Watershed Assessment: O-118 – O-120. USDA. PDF fulltext
• Hynes, H.B.N. (1993): Adults and Nymphs of British Stoneflies. Freshwater Biological Association. ISBN 0-900386-28-2
• Nelson, C. Riley (1996a): Tree of Life Web Project - Capniidae. Winter Stoneflies. Version of 1996-JAN-01. Retrieved 2008-JUL-31.
• Nelson, C. Riley (1996b): Tree of Life Web Project - Plecoptera. Stoneflies. Version of 1996-JAN-01. Retrieved 2008-JUL-31.
• Woodhouse, S.C. (1910): English-Greek Dictionary - A Vocabulary of the Attic Language. George Routledge & Sons Ltd., Broadway House, Ludgate Hill, E.C. Searchable JPEG fulltext
• Zwick, Peter (2000): Phylogenetic System and Zoogeography of the Plecoptera. Annu. Rev. Entomol. 45: 709-746. doi:10.1146/annurev.ento.45.1.709 (HTML abstract)

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