Evaluation of two neem insecticides for non-target effects on the larval parasitoids of the diamondback moth, Plutella xylostella (L.)

The effects of two neem insecticide formulations (an oil-free powder formulation and an oil formulation) on field parasitism of diamondback moth, Plutella xylostella (L.), larvae and, on the longevity and foraging behaviour of Diadegma mollipla (Holmgren), were evaluated in field and laboratory tests. Overall, larval parasitism in plots sprayed with the oil-free neem formulation was not significantly different from that in the water-sprayed plots over the entire observational period, but parasitism in plots receiving the oil formulation was significantly lower during two weeks. Field parasitism by two individual parasitoid species, D. mollipla and Oomyzus sokolowskii (Kurdjumov) showed substantial differences in their relative response to the neem treatments. In laboratory tests, longevity and foraging behaviour of D. mollipla was not affected by contact with the neem insecticide sprays. The results indicate that the neem products may be relatively safe to larval parasitoids of the diamondback moth.