Response of Trichogramma sp. nr. sibericum (Hymenoptera: Trichogrammatidae) to age and density of its natural hosts, the eggs of Rhopobota naevana (Lepidoptera: Tortricidae)

Abstract

Responses of an indigenous Trichogramma sp. nr. sibericum (Hymenoptera: Trichogrammatidae) to the age and density of eggs of the blackheaded fireworm. Rhopobota naevana (Hubner) (Lepidoptera: Tortricidae) were determined in the laboratory. The parasitoid wasp showed a significant (P < 0.05) preference for eggs 1-7-day-old over those 21-day-old. No significant differences (P> 0.05) in percentages of parasitized eggs, however, were found among groups of eggs below 7-day-old. At host egg densities below 20 per wasp, the number of eggs parasitized significantly (P < 0.05) increased with egg density, and tended to stabilize at densities above 30. The rate of parasitism decreased significantly (P < 0.05) with increased host egg density. Superparasitization occurred at densities of 5-10 host eggs, but was rarely observed at densities above 20 eggs. The mean number of progeny per wasp significantly (P < 0.05) increased with host density, whereas the clutch size (the number of parasitoid offspring per parasitized host) significantly (P < 0.05) decreased with an increase in host density.