Heat shock sensitivity of adult male fertility in the parasitoid wasp Anisopteromalus calandrae (Hymenoptera, Pteromalidae)

In insects, decreased reproduction is a sublethal consequence of high temperatures, with males being more sensitive to this in many species. In hymenoptera, arrhenotokous parthenogenesis means that female offspring are produced using sperm and are thus diploid, while males are haploid. Consequently, sperm stocks in males and females (after copulation) are a key regulator of the sex ratio. Anisopteromalus calandrae is a parasitoid wasp in which males can suffer from subfertility due to a drastic decrease in sperm count after exposure to high temperatures during a critical early pupal stage. However, in this species spermatogenesis continues during adulthood, therefore the heat sensitivity of adult males remains to be studied. Laboratory studies were conducted on virgin and previously mated young adult males under control (30 °C) and heat shock (10 min at 48 °C) conditions to exhaust their initial sperm stock. After heat shock, in both virgin and already mated males, the individual sperm potential was half that of controls. Both groups continuously produced sperm, but sperm stock of heat shocked males’ never reached that of the controls. Heat shock reduced survival at 10 days only in previously experienced males but had no impact on the mating ability in competition for a female compared to controls. Despite a reduced sperm count, heat shocked males had fully fertile spermatozoa. Such a physiological response to heat shock in a species with continuous sperm production could be of major interest for both wild populations in a context of temperature variations and parasitoid wasps introduced for agronomical purposes.