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Lethal and Sublethal Effects of Pesticides Used in Western United States Orchards on Hippodamia convergens


We examined the effects of two fungicides (copper+mancozeb and sulfur) and five reduced-risk insecticides (chlorantraniliprole, cyantraniliprole, lambda-cyhalothrin, novaluron, and spinetoram) on Hippodamia convergens (Guerin-Meneville) (Col.: Coccinellidae), an important natural enemy in western United States orchards. Acute toxicity of pesticides was tested via three different exposure routes: oral, residual, and topical. Lambda-cyhalothrin caused significant mortality to adults and larvae via all exposure routes (57-100%). Cyantraniliprole was toxic to adults and larvae when orally exposed, but it was less toxic for other exposure routes. Cyantraniliprole, spinetoram, and novaluron were moderately toxic to larvae when topically exposed (40-63% mortality), but not to adults (<4% mortality). Chlorantraniliprole, copper+mancozeb, and sulfur demonstrated low toxicity (<30% mortality) to adults and larvae, regardless of exposure route. Lethal and sublethal effects were tested by treating insects topically in the inactive stages (egg, pupa) and simultaneously through oral, residual, and topical exposure in the active stages (larva, adult). Larvae were vulnerable to all pesticides except copper+mancozeb, and lambda-cyhalothrin also reduced survivorship for pupae and eggs (3-19%). Exposure to novaluron lowered survivorship for treated eggs (14%) and fertility of treated females (9%). Fecundity was increased by exposure to copper+mancozeb. Corrected acute adult mortality alone was sufficient to detect the harmful effects of chlorantraniliprole and lambda-cyhalothrin, but combined effects of corrected adult mortality and daily fertility were needed to highlight the harmful effect of novaluron. Estimates of the intrinsic rate of increase indicated substantial delays in the population recovery of H. convergens following exposure to chlorantraniliprole, cyantraniliprole, novaluron, and sulfur, and local extinction for lambda-cyhalothrin. The effects of a combination pesticide (chlorantraniliprole and lambda-cyhalothrin) were tested on larvae and adults exposed to residues aged 0, 1, 2, 4, 8, 16, and 38 d in a laboratory or field setting. For field-aged residues, both life stages were highly susceptible to 0 and 1d residue (> 80%), but acute mortality declined for residues aged 16 and 38 d adults (< 53%). For laboratory-aged residues, both life stages had high acute mortality rates (> 80%) regardless of residue age. The rate of decay of the pesticide impact on adults (0.059) was greater than for larvae (0.024) for the field-aged residues, and greater than for adults exposed to laboratory-aged residues (a = 0.004). The results indicate that even reduced-risk insecticides may have harmful effects that vary by pesticide, life stage, and exposure route. Pesticide risk assessments can be improved by using lethal and sublethal data to estimate changes in population growth, and by incorporating both laboratory and field-based bioassays to better understand how pesticides impact natural enemies in the field.

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