Insecticidal toxicity to Trichogramma chilonis Ishii (Hymenoptera: Trichogrammatidae) and subsequent effects on parasitic efficiency and adult emergence rate of descendant generation

Trichogramma chilonis (Ishii) is an important egg parasitoid, widely used as biological control agent of lepidopteran pests. To understand the risks associated with specific insecticide use towards the parasitoid, we studied the effect of 10 insecticides sprayed at recommended field dosages (RFD) on factitious host, Corcyra cephalonica eggs with parasitoid in different development stages, egg (one-day after parasitism), larval (3-days after parasitism), pre-pupal (5-days after parasitism) and pupal (7-days after parasitism). The emerging F-1 adults were further evaluated for parasitic efficiency and reduction in adult emergence of F-2 generation. All the tested insecticides significantly reduced the parasitism of surviving T. chilonis female wasps with varying rates (15.2 to 43.9%). Against pre-imaginal stages, insecticides were comparatively more harmful to the egg and larval stages of parasitoid as compared to pre-pupal and pupal stages. Compared to control values, the parasitism rate of T. chilonis adults and emergence of F-2 adults were also significantly reduced in all the tested insecticides. Chlorantraniliprole, methoxyfenozide and flubendiamide were quite safer to all the developmental stages of the parasitoid, while chlorpyriphos was found to be highly toxic according to the classification given by International Organization for Biological Control (IOBC). Further studies need to be carried out to verify the effect of these insecticides on T. chilonis under semi-field and field conditions.