Biology of Synopeas myles, a parasitoid of the swede midge, Contarinia nasturtii, in Europe

Synopeas myles (Walker) (Hymenoptera: Platygastridae) is a parasitoid of the swede midge, Contarinia nasturtii (Kieffer) (Diptera: Cecidomyiidae), in Europe. We conducted the first thorough investigation of this parasitoid’s biology. Contrary to the biology reported for all platygastrids to date, exposure of late-instar host larvae to parasitism as opposed to eggs or early larvae yielded more S. myles offspring. Superparasitism was relatively common in the field and among groups of females in the laboratory, but was much less common among single females, providing preliminary evidence for self-discrimination. Observation of immature stages of S. myles inside living hosts revealed that supernumerary larvae in superparasitized hosts were probably eliminated by physical combat soon after hatching. With increasing levels of superparasitism, sex ratios of offspring became more female-biased and their mean development time increased. The probability that offspring would emerge from a host and the size of offspring were unaffected by increasing levels of superparasitism.