Relative safety of sprays of two neem insecticides to Diadegma mollipla (Holmgren), a parasitoid of the diamondback moth: effects on adult longevity and foraging behaviour

Abstract

The non-target safety of two neem-based insecticides, Neemroc EC ® (an oil formulation) and Neemros ® (an oil-free powder formulation) to adults of Diadegma mollipla (Holmgren), a larval parasitoid of the diamondback moth, Plutella xylostella (L.), was investigated in laboratory bioassays. The neem insecticides were compared against Karate ® (a synthetic pyrethroid insecticide) and water as sprays. Karate ® caused 100% mortality in treated wasps within 6 h, while the two neem insecticides did not cause any significant mortality. The mean longevity of wasps was not significantly affected by exposure to the two neem insecticides. The time allocation to different components of foraging behaviour by adult females was not significantly altered by the neem treatments. The mean proportion of second instar P. xylostella larvae parasitised by water-sprayed wasps was not significantly different from that of the neem insecticide-sprayed wasps. It is concluded that the field dose rate of the neem insecticides recommended for P. xylostella control did not cause any apparent adverse effects on the survival and foraging behaviour of D. mollipla. Evidently, the neem insecticides are compatible with the activity of D. mollipla and could, therefore, constitute complementary components in the integrated management of P. xylostella on cabbage.