Can agrobiont spiders (Araneae) avoid a surface with pesticide residues?

Integrated pest management includes the use of various pesticides that can have a detrimental effect on spiders. A pesticide can express its activity directly or via residues. Most of the attention paid to the impact of pesticides on spiders has investigated the effects of direct exposure. Our aim in this study was to investigate the residual activity (repellency and toxicity) of selected pesticides on six principal species of spider occurring in an apple orchard. Four of these species (Clubiona spp., Pardosa spp., Philodromus spp., Xysticus spp.) are hunting spiders, and two species (Dictyna spp., Theridion spp.) are web-building. We were interested to see whether these spiders could avoid a surface with residues and to examine their susceptibilities to fresh and 1-day-old residues. For this purpose we conducted laboratory experiments using three types of pesticide, an organophosphate, phosalone (Zolone), a pyrethroid, permethrin (Ambush) and Bacillus thuringiensis (Bt; Novodor), which were applied to paper discs or branches. Spiders could choose to stay on any treated paper/branch within a dish. Except for Theridion spp., all species were repelled by fresh residues but not by 1-day-old residues. Clubiona spp., Dictyna spp., Pardosa spp. and Xysticus spp were repelled by phosalone and permethrin residues only, whereas Philodromus spp. specimens were repelled also by Bt residues. Theridion spp. avoided contact with residues by making a web on any available branch. Regarding toxicity, neither fresh nor 1-day-old residues of phosalone or Bt caused significant mortality to any spider species. In contrast, both fresh and 1-day-old residues of permethrin caused significant mortality to all species except for Theridion spp. In conclusion, spiders can recognise and avoid only fresh residues, although older residues might still be toxic to them.