No 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 (r,) of pea aphid populations was used as a response variable in a 2 X 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 «LCi) 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 (r, 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. KEY WORDS lady beetles, ecotoxicology, exposure, microcosms, neem AFfER YEARS OF strict reliance on chemical pesticides, natural enemies of insect pests are now recognized as essential players in long-term pest control. This shift in attitude toward biological control agents has led to the development of a new generation of less broadly biocidal, botanical pesticides

The effects of Neemix 4.5 EC on predatory Coccinella septempunctata L. larvae were determined after direct spray exposure. First instars were treated by direct application with 0, 40, 100, 200, 400, 600, and 1,000 ppm and 4th instars were treated with 400, 600, 800, and 1,000 ppm azadirachtin, the active ingredient in Neemix. Survivorship and development of the larvae were affected in a dose-dependent manner. Symptoms of exposure included delay or prevention of pupation, blackening of the pupal case, formation of pupal-adult intermediates, and deformation of wings and elytra in adults. To account for the slow action of the pesticide, probit analysis of survivorship data was performed after all surviving larvae from each replicate had emerged as adults: day 16 for 1st instars and day 13 for 4th instars. The LCso values and 95% FL for 1st and 4th instars were estimated to be 1,120 (719-3,677) ppm and 520 (405-600) ppm azadirachtin, respectively. These values were much higher than the recommended rates for control of aphids (3 weekly applications of 20 ppm), suggesting that Neemix might be used in integrated pest management programs because application of rates that control aphids should not result in appreciable mortality of predators. The slopes and intercepts of the probit regression lines were significantly different, indicating that the 2 instars responded to the pesticide differently. Fourth-instar C. septempunctata were innately more sensitive to the growth disrupting effects of acute exposure to Neemix than 1st instars. Disruption of morphogenetic hormone levels is more critical immediately before metamorphosis than during early instars, thus accounting for the differential susceptibility observed. It may be possible for early instars to sustain the effects of Neemix as long as the pesticide is detoxified before the onset of pupation. Our results suggest that it is extremely important to examine> 1 life stage of a species to estimate the total effect of pesticides.