Interspecific foraging response to the thiacloprid treatment of co-existing top spider predators

Neonicotinoids are nicotine-based synthetic insecticides used in agriculture to control plant pests. They are neurotoxic substances that attack the nervous system of insects and can cause paralysis or death. These selective insecticides should have a negligible effect on non-target organisms, including spiders, which are one of the most abundant and diverse natural predators that contribute to the control of pests. Current studies show that selective insecticides such as neonicotinoids have negative effects on non-target invertebrates. They can have both lethal effects resulting in mortality, and sublethal effects involving various aspects of their lives, e.g. breeding, movement, hunting, the ability to defend against predators, and predatory activity.We studied the species-specific responses to neonicotinoid treatments with the active ingredient thiacloprid of two top spider predators coexisting in tree crowns in Europe—respectively, spiders of the genus Philodromus ( aureoles group, Philodromidae) and species Anyphaena accentuata (Walckenaer) (Anyphaenidae). Spiders were exposed to field-realistic concentrations of the tested substance, while the control group was treated with distilled water. We compared the species-specific responses of three components of spider predatory activity: functional response, prey consumption, and overkilling. Further, we observed the long-term survival and paralysis of treated individuals compared to control, and the effect of insecticide residues on predation activity 14 days after insecticide application.We found that an hour-long tarsal contact with the active ingredient thiacloprid reduced predatory activity in both Anyphaena and Philodromus spiders, but the effect was species-specific in many aspects. Feeding was affected by fresh residua in Anyphaena , but not in Philodromus . Furthermore, 14 days after treatment, there were differences in the rates of predation, feeding, and overkilling between species. The treatment caused paralysis, but no mortality in Philodromus . In contrast, the treatment caused significant mortality, but no paralysis in Anyphaena . Further, after 14 days, we found that the insecticide had no significant effect on predation activity. Overall, the study revealed a species-specific response to the given pesticide of top pest predators sharing the same ecological niche in orchards.