Systematic Entomology zyxwvuts (1989) 14,41-92 zyxwvu Review of the Order Strepsiptera JEYARANEY KATHIRITHAMBY Department of Zoology, University of Oxford ABSTRACT. The morphology, biology and life history of the immature stages, the free-living and the neotenic females (of the suborders Mengenillidia and Stylopidia respectively) and the free-living males of the order Strepsiptera are discussed. Strepsiptera are entomophagous para- sitoids and are known to parasitize seven orders and thirty-five families of Insecta. The morphological and physiological changes they cause to the host insect are outlined. The classification of the order is revised; the geographical distribution, phylogenetic system and keys to the families, subfamilies and genera (when possible) are given. As the sexes are dimorphic, separate keys are provided for adult males and neotenic females. zyxwv Introduction The Strepsiptera is a small cosmopolitan order of insects (Table 1). They are entomophagous parasitoids of a unique kind which exhibit extreme sexual dimorphism. Many of the known species are described solely from adult free- living, short-lived males, since (except in one family zyxwvutsr - Mengenillidae) the permanently endo- parasitic females are neotenic. Being devoid of such adult features as eyes, wings, legs and external genitalia, females are difficult to iden- tify taxonomically. The hosts of Strepsiptera are other insects. Species are known to attack Thysanura (Lepismatidae), Blattodea (Blattidae), Man- todea (Mantidae), Orthoptera (Gryllidae, Gryllotalpidae, Tettingoniidae, Tridactylidae), Hemiptera (Homoptera - Cercopidae, Cica- dellidae, Membracidae, Delphacidae, Dictyo- pharidae, Eurybrachyidae, Ricaniidae, Flatidae, Fulgoridae, Issidae, Tettigometridae; Heteroptera - Coreidae, Cydnidae, Lygaeidae, Correspondence; Dr J. Kathirithamby, Department of Zoology, South Parks Road, Oxford OX1 3PS. Pentatomidae, Scutelleridae), Diptera (Tephritidae, Platysomatidae) and Hymeno- ptera (Formicidae, Mutillidae(?), Masaridae, Eumenidae, Vespidae, Sphecidae, Colletidae, Halictidae, Andrenidae). Some of the hosts are economic pests. For example, Nilaparvata lugens Stil and Sogatella furcifera HorvAth (Homoptera: Delphacidae), which spread virus diseases and cause ‘hopper burn’ in rice in South and South East Asia, are parasitized by Elenchus sp. ; Javesella pellucida (F.) (Homoptera: Delphacidae), a vector of a virus disease in oats in the Palaeartic Region, is parasitized by Elenchus tenuicornis (Kirby); Nephotettix sp. (Homoptera: Cicadellidae), a vector of a virus disease in rice in South and East Asia, is parasitized by Halictophagus sp. ; fruit flies (Diptera: Tephritidae) that damage fruits in Australia and South East Asia are parasitized by Dipterophagus daci Drew & Allwood; Segestes decoratus Redtenbacher, Sexava nubila (StB1) and Segestidae novaeguineae (Brancsik) (Ortho- ptera: Tettigoniidae), which feed on the fronds and cause severe defoliation of coconuts, oil palm and Pandanus spp. in Papua New Guinea, are parasitized by Stichotrema dallatorreanum 41