Family EUSTHENIIDAE

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Introduction

The family (its name sometimes misspelt in the literature as Eusthenidae) includes the large stoneflies from Australia, New Zealand and South America. Its sister family, Diamphipnoidae, is known only from South America. Eustheniidae do have primitive characters, but also have derived characters unique to the family. Two of the three subfamilies originally described by Tillyard are retained: Eustheniinae and Stenoperlinae. Both subfamilies, now with an Australian total of three genera, 15 species and four subspecies, are known from Australia. Of these, only the genus Stenoperla is not endemic to Australia; two species are found in New Zealand, but none in Tasmania.

The biology of the Eustheniidae is imperfectly known throughout Australia. Studies of Victorian species and Stenoperla spp. in New Zealand suggest that nymphs typically are found in swift streams and rivers on an eroding substrate of stones and gravel. Nymphs are carnivorous yet slow-growing with a life-span of two to three years. Some species are autumnal, e.g. Thaumatoperla spp., but emergence periods may extend over many months, even at a single locality. Adults of some genera are clumsy and run rather than fly, but Stenoperla and Eusthenia fly well. Adults may feed on rotten wood, except for Stenoperla australis, which does not feed. Thaumatoperla alpina has been reported to feed on silky daisy, Calmisia sericophylla.

The family appears to be monophyletic based on the molecular results of Letsch et al. (2021).

Diagnosis

Adults: large insects (wing span up to 65 mm), differentiated by their spectacular colouration and degree of brachyptery, which involves rounding and broadening of the wings. Large mola. In prothorax, attachment of the sternal depressor of the trochanter shifted across twisted bases of furcal arms to near spina. Last abdominal ganglion shifted into segment 7 from segment 8. Tibia with single medially displaced apical spur. Notch between main part of wing and neala of the hind wing reduced, contour regularly curved.

Nymphs: large (up to 49 mm long), often greenish, with long filamentous gills on abdominal segments 1–6 (Eustheniinae) or segments 1–5 (Stenoperlinae). Gills are present in a reduced form in newly hatched larvae and occur as large remnants in adult life.

Eggs: with a pigmented leather-like chorion and a tough surrounding membrane, laid in a monolayer on the underside of stones and logs, washed (Stenoperla) from the tip of the abdomen or dropped in a large solid mass (Thaumatoperla). Only Stenoperla has fully developed eggs (without egg coats) in ripe adult females.

General References

Hynes, H.B.N. 1974. Observations on the adults and eggs of Australian Plecoptera. Australian Journal of Zoology Supplementary Series 29: 37-52

Letsch, H., Simon, S., Frandsen, P., Liu, S., Machida, R., Mayer,C., Misof, B., Niehuis, O., Zhou,X., Wipfler, B. 2021. Combining molecular datasets with strongly heterogeneous taxon coverage enlightens the peculiar biogeographic history of stoneflies (Insecta: Plecoptera). Systematic Entomology 46: 952-967 [958]

Neboiss, A. 1959. Further discoveries on Victorian Plecoptera. Memoirs of the National Museum of Victoria, Melbourne 24: 37-44

Theischinger, G. 1983. The genus Stenoperla McLachlan in Australia (Insecta: Plecoptera: Eustheniidae). Australian Journal of Zoology 31: 541-556

Theischinger, G. & Cardale, J.C. 1987. An illustrated guide to the adults of the Australian stoneflies (Plecoptera). CSIRO Australia. Division of Entomology Technical Paper 26: 1-83

Tillyard, R.J. 1921. Revision of the family Eustheniidae (Order Perlaria), with descriptions of new genera. Proceedings of the Linnean Society of New South Wales 46: 221-236

Zwick, P. 1979. Revision of the stonefly family Eustheniidae (Plecoptera) with emphasis on the fauna of the Australian region. Aquatic Insects 1: 17-50

Zwick, P. 1981. Plecoptera. pp. 1171-1182 in Keast, A. (ed.). Ecological Biogeography of Australia. The Hague : Junk Vol. 2.

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