Temperature-dependent effect of two neurotoxic insecticides on predatory potential of Philodromus spiders

Abstract

Although temperature significantly influences pesticides’ impact on ectotherms, the joint effect of temperature and pesticides on natural enemies is understudied. In laboratory conditions, we investigated the influence of two commonly used insecticides, spinosad and λ-cyhalothrin, on mortality and functional response of a community of Philodromus spiders (P. cespitum 80 %, P. albidus 20 %) at different temperatures (10, 17, 25, and 31 °C). Almost all spiders died at 31 °C in the λ-cyhalothrin treatment. Mortality was very low at other temperatures. Mortality in the spinosad treatment did not differ from the control. Both pesticides reduced the prey capture rate and/or changed the type of functional response at all temperatures. The sublethal effects of λ-cyhalothrin were most pronounced at 10 °C, while those of spinosad were most marked at 10 and 25 °C. At 10 °C, the pesticides’ effects on the spiders were long lasting. In addition, λ-cyhalothrin influenced the philodromids much more negatively than spinosad suggesting its incompatibility with IPM across all temperatures. The results support the importance of studying the temperature-specific effects of pesticides in order to increase the efficiency of integrated pest management. Philodromids are effective in pest suppression at low temperatures, but application of pesticides at the beginning of the season can significantly disrupt their biocontrol potential.