Order STREPSIPTERA

Strepsiptera

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Order STREPSIPTERA

Strepsipterans

Compiler and date details

31 December 1994 - T.R. New, Department of Zoology, La Trobe University, Bundoora, Victoria, Australia

Introduction

The Strepsiptera are a small, widely distributed order of highly specialised parasitoids. The order comprises nine families, six of which occur in Australia. Historically, these small insects have been grouped with the Coleoptera and have been included (as superfamily Stylopoidea or family Stylopidae) within that order. They are now generally recognised as distinct at the ordinal level (Kathirithamby 1991), but the complex history of their higher relationships is reviewed by Lawrence et al. (1995).

Strepsiptera are characterised by remarkable sexual dimorphism. Free living males are winged, and females of all taxa except Mengenillidae are neotenic and do not leave their insect hosts; they lack wings, legs, eyes, and distinctive genitalic structures. Males have small elytriform or haltere-like forewings and large hind wings—the metathorax is consequently much larger than the other thoracic segments. Male Strepsiptera are unique among insects in lacking a trochantin (as do female Mengenillidae), and the head is also very characteristic. Antennae are 4–7-segmented, and one or more segments are flabellate; eyes are very large, with well defined facets; and the mouthparts are reduced to mandibles and maxillae, one or both pairs often reduced.

Male Strepsiptera are apparently shortlived, those of some species perhaps surviving for only a few hours. Most species have been described only from this sex, as males can be captured in suction traps, light traps and by other such methods.

Strepsiptera are endoparasitoid in several groups of insects, with varying levels of host specificity at the family or species levels. Particular species are known to attack Thysanura, Blattodea, Mantodea, Orthoptera, Hemiptera, Diptera or Hymenoptera (Kathirithamby 1989a) with Hemiptera and Hymenoptera the predominant hosts of the order. Early work, involving mainly aculeate Hymenoptera hosts, showed that the parasitoid causes morphological changes to the hosts, collectively termed 'stylopisation' and including forms of parasitic castration. Superparasitism and multiparasitism have been recorded.

The life cycle is complex, involving viviparity and larval heteromorphosis. After mating in situ with males attracted by pheromones, females (other than Mengenillidae) produce large numbers of active triungulin larvae which are released just outside the parental host. These larvae need to find a fresh host. If hosts are Homoptera, immature hosts must be discovered directly by larvae; if Hymenoptera, triungulins need to be carried by a foraging bee or wasp back to the nest, where they can attack early instar larvae. Triungulins enter the host and moult to a vermiform larva which may undergo up to six parasitic instars—Kathirithamby et al. (1984) detailed only four for Elenchus tenuicornis Kirby. The pupal stage is suppressed in females. In males, the pupa is adecticous and exarate, and the empty puparium is left within the host. Effects of parasitisation typically include protraction of host development, which helps to assure parasitoid survival.

The order Strepsiptera includes about 540 described species: Kathirithamby (1989a) cited 520 species, but the fauna of many parts of the world is very poorly known. For the Australian fauna, recent studies by Kathirithamby (1988–1993) have laid a firm foundation of knowledge. Prior to these studies, only a few species had been described in isolation. Perkins (1905) described several species that parasitise economically important leafhopper pests in sugar cane plantations, but most other records were single species descriptions or records, some of which are now difficult to verify. Early reviews of the order by Pierce (1909) and Bohart (1941) were followed by more comprehensive appraisals by Kinzelbach (1971a, 1971b) and Kathirithamby (1989a), and these accounts are indispensable to students of Strepsiptera.

Division of the order into two suborders, Mengenillidia and Stylopidia, by Kinzelbach (1969) has been accepted generally. The former comprises two families, of which Mengeidae are known only from fossils in amber. The seven families in Stylopidia are all extant.

Diversity of the Australian fauna has been estimated variously at 93 species (Riek 1970) and around 159 species (Kathirithamby 1991), with the latter estimate based on direct appraisal of most available collections. However, published information on several families is still fragmentary. Although several genera of Stylopidae, in particular, are noted in these general accounts as occurring in Australia, no species descriptions or other significant information on their incidence are yet available, and only two of a suggested 20 species of Mengenillidae have been named. This Catalogue is thus inevitably somewhat 'unbalanced' in the perspective it conveys, but it represents the situation at the end of 1994, the cut-off time for this section of the Catalogue. The identity of taxa noted in the general accounts cited above has not been confirmed, and Kathirithamby (1992) further noted the existence of two undescribed genera of Stylopidae in Australia. The poorly known genera are Hylechthrus Saunders, 1850, Halictoxenos Pierce, 1908, Xenos Rossius, 1793, and Pseudoxenos Saunders, 1872 (Stylopidae). According to Kathirithamby (1993), the Stylopidae are the largest family in Australia, with an estimated 65 species.

Acknowledgements

I am especially grateful to Mrs Tracey Carpenter who undertook much of the data entry for this section of the Catalogue, and to the library staff of La Trobe University for obtaining several obscure references. Financial support from Australian Biological Resources Study (ABRS) is acknowledged gratefully, together with considerable patient editorial advice from Dr A. Wells and helpful comments from referees. The illustrations were provided by, and are reproduced with permission from, the CSIRO Division of Entomology and the Melbourne University Press.

Database Notes

The information on the Australian Faunal Directory site for the Strepsiptera is derived from the Zoological Catalogue of Australia database compiled on the Platypus software program. It incorporates changes made to the work published on 15 August 1996 as (New, T.R., 1996)

Limital Area

Distribution data in the Directory is by political and geographic region descriptors and serves as a guide to the distribution of a taxon. For details of a taxon's distribution, the reader should consult the cited references (if any) at genus and species levels.

Australia is defined as including Lord Howe Is., Norfolk Is., Cocos (Keeling) Ils, Christmas Is., Ashmore and Cartier Ils, Macquarie Is., Australian Antarctic Territory, Heard and McDonald Ils, and the waters associated with these land areas of Australian political responsibility. Political areas include the adjacent waters.

Terrestrial geographical terms are based on the drainage systems of continental Australia, while marine terms are self explanatory except as follows: the boundary between the coastal and oceanic zones is the 200 m contour; the Arafura Sea extends from Cape York to 124 DEG E; and the boundary between the Tasman and Coral Seas is considered to be the latitude of Fraser Island, also regarded as the southern terminus of the Great Barrier Reef.

Distribution records, if any, outside of these areas are listed as extralimital. The distribution descriptors for each species are collated to genus level. Users are advised that extralimital distribution for some taxa may not be complete.