ENTOMOPATHOGENIC NEMATODES (RHABDITIDA, STEINERNEMATIDAE) - TOXICITY OF NEEM

The effects of Margosan-O, a commercial neem-based insecticide, on the entomopathogenic nematode species Steinernema carpocapsae (Steiner), S. feltiae (Filipjev), and S. glaseri (Steiner) were examined in this study. Both acute and chronic toxicity were estimated, as were effects on nematode infectivity after incubation with the insecticide. Margos an-O was toxic to all 3 species, but only at much higher concentration s than the recommended field rate of 20 mg azadirachtin/liter water. T he acute LC(50) and 95% FL for S. carpocapsae exposed to Margosan-O wa s 425 (341-501) mg azadirachtin per liter. Chronic toxicity was not si gnificantly different from acute toxicity until the 15th d of incubati on. The acute LC(50) and 95% FL for S. feltiae was 380 (340-443) mg az adirachtin per liter. Chronic toxicity values were not significantly d ifferent until day 15. The susceptibility of S. feltiae increased grea tly between 12 and 15 d of incubation with Margosan-O. The acute LC(50 ) and 95% FL for S. glaseri was 351 (330-370) mg azadirachtin per lite r. Unlike the other 2 species I detected no difference in susceptibili ty among incubation times for S. glaseri. When the 3 species were comp ared, susceptibility to Margosan-O at LC(50) at each incubation time i nterval was not significantly different until day 15. S. feltiae was s ignificantly more susceptible than the other species after exposure to Margosan-O for 15 d. Infectivity [measured as the ability to kill gre ater waxmoth larvae, Galleria mellonella (L.), contained in well plate s], was reduced in all 3 species only when they had been incubated wit h Margosan-O at concentrations >200 mg azadirachtin per liter. When Ma rgosan-O and nematodes were applied together at field rates to soil, i nfectivity was not reduced.