Effects of two reduced-risk insecticides on the egg parasitoid Trichogramma minutum in apple orchards

Abstract: Trichogramma minutum Riley is an egg parasitoid found in North American apple orchards where it contributes to the biological control of several lepidopteran pests including the codling moth, Cydia pomonella (L.). To control this major pest, reduced-risk insecticides have been commonly applied in Quebec orchards for several years. We investigated the compatibility of these insecticides with the biological control agent T. minutum in field and laboratory experiments. In an experimental orchard, codling moth eggs were exposed to parasitism a few days prior or after the application of either novaluron, chlorantraniliprole or water (control). For each egg cohort, the emergence of Trichogramma adults from the codling moth eggs was significantly lower for novaluron than chlorantraniliprole and control. In laboratory experiments, we evaluated the effects of these insecticides on the development ofthe immature stages of T. minutum. Eggs were treated 24 and 120 h after parasitism. Results indicated that the development of Trichogramma from the egg to pupal stage was not affected by the treatment. Similar results were observed for their development from the pupal to adult stage. The results suggest that the inhibition of chitin synthesis associated with novaluron did not affect the development of immature stages of T. minutum but may affect specialized structures such as mandibles used by Trichogramma during the emergence process.