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Multiple Routes of Pesticide Exposure and the Risk of Pesticides to Biological Controls: A Study of Neem and the Sevenspotted Lady Beetle (Coleoptera: Coccinellidae)

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Abstract:

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 spray exposure to a commercial neem pesticide. The instantaneous rate of increase (r1) of pea aphid populations was used as a response variable in a 2 × 3 factorial experiment. Microcosms were treated with 100 ppm (mg/liter) or 600 ppm azadirachtin, the active ingredient in the commercial neem insecticide, or with water in the presence or absence of adult or 4th instar lady beetles. We compared our results with those of a previous study where C. septempunctata was exposed to only 1 route of exposure, direct application. Results from the previous study indicated that 100 ppm of the neem insecticide was sublethal (1) and 600 ppm was equivalent to the LC62 for 4th instars. Both concentrations 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 (r1 values) of the aphid populations 4 d after treatment were compared with 2-way analysis of variance. The pesticide alone and the predator alone caused a significant decrease in aphid population growth rates. However, no significant (P > 0.05) interaction between the predator and the pesticide was detected indicating that the chemical and biological control agents are not working synergistically. Furthermore, exposure to the pesticide in micrososms significantly reduced or completely eliminated oviposition in adult C. septempunctata, and all of the larval lady beetles exposed to 100 or 600 ppm died within 10 d of treatment. Based on these results, we question the value of toxicity tests where only 1 route of pesticide exposure is considered.

Document Type: Research Article

Publication date: February 1, 1998

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  • Journal of Economic Entomology is published bimonthly in February, April, June, August, October, and December. The journal publishes articles on the economic significance of insects and is divided into the following sections: apiculture & social insects; arthropods in relation to plant disease; forum; insecticide resistance and resistance management; ecotoxicology; biological and microbial control; ecology and behavior; sampling and biostatistics; household and structural insects; medical entomology; molecular entomology; veterinary entomology; forest entomology; horticultural entomology; field and forage crops, and small grains; stored-product; commodity treatment and quarantine entomology; and plant resistance. In addition to research papers, Journal of Economic Entomology publishes Letters to the Editor, interpretive articles in a Forum section, Short Communications, Rapid Communications, and Book Reviews.
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