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 organisms. They can have both lethal effects resulting in mortality, and sublethal effects involving various aspects of their lives, e.g. breeding, movement, hunting, ability to defend against predators, and predatory activity. We studied the species-specific responses to neonicotinoid treatment 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 functional response and two components of predation rate: feeding and overkilling. Further, we monitored long-term survival and recovery from paralysis compared to control, and the impact of insecticide residues on predation rate 14 days post-exposure. We found that a one-hour tarsal contact with thiacloprid significantly reduced predation rate in both Anyphaena and Philodromus spiders, although the effects were highly species-specific. In Anyphaena, feeding was inhibited by fresh treatment, whereas Philodromus remained unaffected in this regard. Furthermore, the rate of overkilling significantly decreased under the fresh treatment in both species. The treatment induced a reversible paralysis in Philodromus, whereas it caused significant mortality in Anyphaena. Furthermore, 14 days post-treatment, the insecticide had no significant effect on feeding of either species, while the overkilling in Philodromus remained significantly lower than in the control. Overall, the study demonstrates a species-specific response to thiacloprid among top pest predators that share the same ecological niche in orchards.