Lethal and sublethal effects of neem on Aphis gossypii and Cycloneda sanguinea in watermelon

Resumo

The objective of this study was to evaluate the impact of oil extract of neem, Azadirachta indica, on the watermelon aphid Aphis gossypii and its natural enemy Cycloneda sanguinea. Toxicity bioassays were conducted with the commercial product DalNeem (1,475 g L^-1 azadirachtin) at 0.0037 µg a.i. mL^-1, 0.0074 µg a.i. mL^-1 and 0.0148 µg a.i. mL^-1, Malathion at 1 µg a.i. mL^-1 and distilled water as a control treatment. The products were sprayed to watermelon leaf discs, and the insects were exposed to the product residues. The instantaneous population growth rate of A. gossypii and the survival of C. sanguinea larvae exposed to the different treatments were calculated. A decrease in the instantaneous population growth rate of A. gossypii with increasing concentrations of neem was observed, and the aphids did not reproduce on the leaf discs treated with malathion during the first 24 hours of exposure due to its rapid lethal effect on adult insects. The larvae of the predator C. sanguinea exposed to malathion survived only for 24 hours. The survival of the predator exposed to different concentrations of neem was also significantly reduced compared to the predators exposed only to water. However, laboratory experiments may overestimate the effect of neem on predators because the individuals cannot employ escape behavior caused by neem repellency.