Effects of Ddt and Fenitrothion on Field-Collected Larvae of a Eucalypt-Defoliating Beetle, Paropsis Atomaria Ol. Ii. Effects of Treatment of the Host on the Parasitoids.

Abstract

Treatment of larvae of Paropsis atomaria Ol. with DDT or fenitrothion resulted in the death of a larger proportion of parasitized than non-parasitized larvae. Larvae parasitized by Eadya paropsidis Huddleston & Short were more susceptible to the insecticides than those parasitized by tachinids, resulting in a markedly changed balance of parasitoids in survivors. After insecticide treatment of hosts, development and emergence of parasitoids from survivors were not affected. Nor were ovaries of parasitoids emerging from treated hosts different from those of controls. Although ovaries of Perilampus tasmanicus Cameron were not affected by the insecticides applied to the Paropsis larvae, they were affected by their host: whereas Perilampus adults from tachinid hosts were synovigenic, those from Eadya were not. Perilampus adults from Eadya also were lighter than those from tachinids, spent from twice to five times as long in the pupal stage, and, when they did emerge, tended to have deformed ovaries. Eadya suffered high mortality, even in controls. This mortality probably occurs in weaker hosts less able to support the level of parasitization, because hosts from which Eadya failed to pupate were lighter than those from which it pupated successfully.