Role of the egg parasitoid Trichogramma minutum in biological control of the grape berry moth, Endopiza viteana

During a survey for natural enemies of the grape berry moth (GBM) Endopiza viteana (Clemens) in northwestern Pennsylvania, we found that Trichogramma minutum Riley is the only native egg parasitoid with the potential to limit berry damage by preventing egg hatch. Natural parasitism, however, was found to be unreliable for providing economic pest suppression. Early season populations of the parasitoid are extremely low and may be the result of inadequate alternative host eggs for overwintering. Also, wild grapes and their wooded habitats were found to be favored by T. minutum. Parasitism was low in cultivated grapes and in wild grapes growing close to commercial vineyards (possibly due to the deterrent effect of insecticides) and highest in sites ≅1.5 km from commercial vineyards. Adult T. minutum emerging from GBM eggs were exceptionally small and showed little vigor. Parasitized eggs often failed to produce adult parasitoids. Pre-adults in such eggs had poorly formed mouth-pans or lacked them altogether. Inundative releases of laboratory-reared T. minutum in border rows of vineyards are suggested as a possible alternative to the current practice of applying carbamate and organophosphate insecticides, which are inimical to beneficial arthropods.