IMIS

Strepsiptera are bizarre insects with unusual morphology often referred to as “twisted-wing” parasitoids, (Kinzelbach 1971a; Kathirithamby 1989, 2009, 2018). They are a small order of holometabolous insects, cosmopolitan in distribution (except for one family), and are found in all habitats occupied by insects, except the aquatic. They comprise 15 families, 5 of which are extinct. Strepsiptera parasitize a broad range of hosts, encompassing Apterygota, Exopterygota and Endopterygota, belonging to 7 orders and 35 families of Insecta. Hosts include Blattodea, Diptera, Hemiptera, Hymenoptera, Mantodea, Orthoptera, and Zygentoma (Kinzelbach 1971; Kathirithamby 1989, 2009, 2018).

All species are obligate endoparasitoids for all three of their larval stages. Within holometabolan insects, strepsipterans offer a classical example of dramatic differences between the sexes. Males are free-living as adults, with large raspberry-like eyes, flabellate antennae, shortened forewings and large hind wings. In Mengenillidae both males and females emerge to pupate externally from the host, while the free-living adult females of Mengenillidae are wingless. In Stylopidia, endoparasitism continues through the pupal stages in the males, while the females are neotenic, and remain permanently embedded in the host up to maturity, except for the extruded cephalothorax, and even up to the production of the motile first‐instar planidia. On entry into a new host, the host-seeking planidia become apodous larvae.

Strepsiptera display unusual genetic characteristics: they possess one of the smallest insect genomes (108 Mbp) (Johnston et al. 2004), yet have one of the larger 18S ribosomal DNA sequences, associated with a number of unique and unusually long insertions (Gillespie et al. 2005, Matsumoto et al. 2011), and there are two transfer RNA translocations that disrupt an otherwise ancestral insect mitochondrial genome (McMahon et al. 2009). Both the mitochondrial DNA and the nuclear ribosomal DNA underwent a significant burst of molecular evolution in the early history of Strepsiptera (McMahon et al. 2011). The first molecular phylogeny of Strepsiptera revealed that there are nine families with two suborders: the basal Mengenillidia and the derived Stylopidia (McMahon et al. 2011). Molecular studies support a node uniting Strepsiptera with Coleoptera (Niehuis et al. 2012; Boussau et al. 2014).

The life cycle of Strepsiptera is in synchrony with the host it parasitizes. Most described species are the short-lived males, and caught in traps. The endoparasitic female Stylopidia are found with their hosts. Whenever possible, host records are provided in the database, but often it is unrecorded for the free-living males. In one family, the Myrmecolacidae, males and females parasitize not only hosts from different genera but from different families: males parasitize ants (Hymenoptera: Formicidae), and females parasitise grasshoppers (Orthoptera: Tettigoniidae) and mantids (Mantodea: Mantidae). In this instance, the sexes can only be matched by molecular characterization (Kathirithamby and Hamilton 1992; Kathirithamby and Johnston 2004; Kathirithamby et al. 2009; Hayward et al. 2011)

Strepsiptera have been described from Burmese, Baltic, Fushun and Dominican ambers, Eocene compressions of Messel and Geiseltal, and from shale in the Green River Formation (Kathirithamby 2018). Much has yet to be discovered about the biodiversity of this insect order, primarily because of their tiny size, reclusive nature, and the extremely brief life of the free‐living adult male.