Box 5.1. Courtship and mating in Mecoptera
Sexual behavior has been well studied in hangingflies (Bittacidae) of the North American Hylobittacus (Bittacus) apicalis and Bittacus species and the Australian Harpobittacus species, and in the Mexican Panorpa scorpionflies (Panorpidae). Adult males hunt for arthropod prey, such as caterpillars, bugs, flies, and katydids. These same food items may be presented to a female as a nuptial offering to be consumed during copulation. Females are attracted by a sex pheromone emitted from one or more eversible vesicles or pouches near the end of the male’s abdomen as he hangs in the foliage using prehensile fore tarsi.
Courting and mating in Mecoptera are exemplified by the sexual interactions in Harpobittacus australis (Bittacidae). The female closely approaches the “calling” male; he then ends pheromone emission by retracting the abdominal vesicles. Usually the female probes the prey briefly, presumably testing its quality, while the male touches or rubs her abdomen and seeks her genitalia with his own. If the female rejects the nuptial gift, she refuses to copulate. However, if the prey is suitable, the genitalia of the pair couple and the male temporarily withdraws the prey with his hind legs. The female lowers herself until she hangs head downwards, suspended by her terminalia. The male then surrenders the nuptial offering (in the illustration, a caterpillar) to the female, which feeds as copulation proceeds. At this stage the male frequently supports the female by holding either her legs or the prey that she is feeding on. The derivation of the common name “hangingflies” is obvious!
Detailed field observations and manipulative experiments have demonstrated female choice of male partners in species of Bittacidae. Both sexes mate several times per day with different partners. Females discriminate against males that provide small or unsuitable prey either by rejection or by copulating only for a short time, which is insufficient to pass the complete ejaculate. Given an acceptable nuptial gift, the duration of copulation correlates with the size of the offering. Each copulation in field populations of Ha. australis lasts from 1 to a maximum of about 17 minutes for prey from 3 to 14 mm long. In the larger Hy. apicalis, copulations involving prey of the size of houseflies or larger (19–50 mm2) last from 20 to 29 minutes, resulting in maximal sperm transfer, increased oviposition, and the induction of a refractory period (female non-receptivity to other males) of several hours. Copulations that last less than 20 minutes reduce or eliminate male fertilization success. (Data after Thornhill 1976; Alcock 1979.)