Effects of neem-fed prey on the predacious insects Harmonia conformis (Boisduval) (Coleoptera: Coccinellidae) and Mallada signatus (Schneider) (Neuroptera: Chrysopidae)

The effects of the exposure of predators indirectly to neem seed extracts was tested by the feeding of Harmonia conformis (Boisduval) adults and Mallada signatus (Schneider) larvae with prey (second-instar Helicoverpa armigera (Hubner) larvae) that had eaten neem oil solution. Results from three treatments (50 and 200 ppm azadirachtin and 50 ppm endosulfan, a pesticide compound) were compared to those of a control, distilled water. We found that 50- and 200-ppm azadirachtin treatments were not toxic to H. conformis adults and M. signatus larvae, but there are some effects on metamorphosis of M. signatus. The effect on the number of second-instar H. armisera consumed was an increase in consumption in the 200-ppm azadirachtin treatment by M. signatus larvae, caused by the 200-ppm azadirachtin treatment delaying pupation. Both azadirachtin treatments had negative effects on M. signatus pupal survival, with the 200-ppm treatment killing all individuals, and about 50% being affected by the 50-ppm treatment. The results suggest that, although the biopesticide azadirachtin has been thought useful in biological control, assuming that the indirect effects of this compound is not enhanced by any direct exposure of the natural enemies to the chemical in the field, application of this material still should be careful, especially in high concentrations, because of its obvious insect growth regulatory (IGR) effects on M. signatus, which is one of the important predators in cotton fields. If persistent natural enemy populations are required, the rate of azadirachtin application will need to be adjusted because consumption of the compound by M. signatus larvae resulted in pupal death. Whether H. conformis or M. signatus can be used against H. armigera in the field will need to be tested further. (C) 2001 Academic Press.