Effect of temperature and parasite density on three species of Aphytis (Hymenoptera: Aphelinidae), parasitising California red scale

Summary Three species of Aphytis parasites of California red scale, Aonidiella aurantii (Maskell) were each confined at different densities with approximately equal numbers of scale insects at several constant temperatures to determine the effect of these factors on progeny production and distribution and the search rate. Egg location on the host body by the parasites was unaffected by temperature or parasite density. A. melinus laid its eggs both dorsally and ventrally in equal proportions while A. lingnanensis and A. chrysomphali laid their eggs ventrally. Progeny production by A. melinus and A. lingnanensis increased at the higher temperature; that of A. chrysomphali did not. Unlike the other species, A. chrysomphali failed to oviposit at 32°C. Although increasing parasite density reduced progeny production in both A. melinus and A. lingnanensis, they were able to maintain an almonst constant search rate. This was due to their ability to distribute their eggs among the hosts more regularly at the higher parasite densities. While the mechanism of this process is easy to understand for A. melinus which behaved as a gregarious parasite, it is unclear for A. lingnanensis, which is almost a solitary parasite. The progeny production and the search rate of A. chrysomphali dropped significantly with increasing parasite density.