Order STREPSIPTERA (Twisted-wing Parasites)
Stylops pacifica, male, photo by E.S. Ross (Note: not a BC species)
(Fig. 101)


Strepsiptera: from the Greek strepsis, = twisting, and ptera = wings.

Strepsiptera is a small order (about 450 described species) of rarely encountered parasitic insects which undergo hypermetamophosis. In one family both males and females leave the host to pupate and are free-living as adults. In all other families, including the family found in British Columbia, both sexes pupate within the host but only the males leave the host. The free-flying males are very short-lived, in BC species living only 6-8 hours. The females are neotenic and remain in the host with only the anterior part of the cephalothorax extruded between the abdominal segments of the host. The body of the female nearly completely fills the abdomen of the host causing suppression of the sexual development of the host but also leading to a longer life for the host. The young are produced live and have eyes and legs and are active in searching for appropriate hosts. Once the larva enters the host, it moults into a legless wormlike parasite which feeds in the body cavity of the host and undergoes several moults before pupating within the final larval skin.

Although any given strepsipteran species will accept only one or a few host species, as an order they attack members of eight other orders of insects: Thysanura, Blattodea, Mantodea, Orthoptera, Homoptera, Hemiptera, Diptera and Hymenoptera. The members of one family of Strepsiptera, males and females parasitize members of different orders, males in ants and females in Orthoptera and Mantodea.

Adult males have six legs and three body segments as is usual in insects. They have protruding eyes and antennae with often well developed lateral processes. The forewings are small haltere-like structures while the hind wings are large very characteristic batwing-like structures with only longitudinal veins. Females usually lack eyes, antennae and legs and have very indistinct body segments.

There are eight extant families globally with five found in North America, three known from Canada but only one reported from British Columbia.

Description of Family
Family Stylopidae (Fig. 101 & 102)
This is the largest and most widespread family in Strepsiptera with its member species being parasites of wasps and several families of solitary bees. Adult males are characterized by four-segmented tarsi with no claws, antenna with 4- or 6 segments and mandibles knife-shaped and crossed distally. The final instar females have a flattened but not shortened cephalothorax with 2-5 genital pores and brood canals with slit-shaped openings.

Two genera of Stylopidae are known from British Columbia: Stylops Kirby and Xenos Rossius. The genus Stylops, are parasites of Andrena sp., and characterized by adult males with 6-segmented antennae (namely, Stylops advarians Pierce (host presumably Andrena advarians Vier.), S. leechi Bohart (host: A. advarians Vier., and S. shannoni Pierce (host: A. hippotes Robertson). The single species of Xenos, namely, Xenos peckii Kirby (host: Polistes fuscatus (Fabricius)), is a parasite of Polistes sp., and is characterized by adult males with 4-segmented antennae.