MULTIPLE ROUTES OF PESTICIDE EXPOSURE AND THE RISK OF PESTICIDES TO BIOLOGICAL-CONTROLS - A STUDY OF NEEM AND THE SEVENSPOTTED LADY BEETLE (COLEOPTERA, COCCINELLIDAE)

Microcosms were used to illuminate community-level interactions among the pea aphid, Acyrthosiphon pisum Harris (Homoptera: Aphididae), and the sevenspotted lady beetle, Coccinella septempunctata L., after a sp ray exposure to a commercial neem pesticide. The instantaneous rate of increase (r(t)) of pea aphid populations was used as a response varia ble in a 2 x 3 factorial experiment. Microcosms were treated with 100 ppm (mg/liter) or 600 ppm azadirachtin, the active ingredient in the c ommercial neem insecticide, or with water in the presence or absence o f adult or 4th instar lady beetles. We compared our results with those of a previous study where C. septempunctata was exposed to only 1 rou te of exposure, direct application. Results from the previous study in dicated that 100 ppm of the neem insecticide was sublethal (<LC1) and 600 ppm was equivalent to the LC62 for 4th instars. Both concentration s caused no mortality to adults based on direct application. However, in the current study, C. septempunctata was exposed to direct sprays, residues on leaves, and pesticide-contaminated prey. Population growth rates (r(t) values) of the aphid populations 4 d after treatment were compared with e-way analysis of variance. The pesticide alone and the predator alone caused a significant decrease in aphid population grow th rates. However, no significant (P > 0.05) interaction between the p redator and the pesticide was detected indicating that the chemical an d biological control agents are not working synergistically. Furthermo re, exposure to the pesticide in micrososms significantly reduced or c ompletely eliminated oviposition in adult C. septempunctata, and all o f the larval lady beetles exposed to 100 or 600 ppm died within 10 d o f treatment. Based on these results, we question the value of toxicity tests where only 1 route of pesticide exposure is considered.