Influence of Imidacloprid and Horticultural Oil on Spider Abundance on Eastern Hemlock in the Southern Appalachians

Neonicotinoid insecticides limit the potential of spiders to re-colonize disturbed agroecosystems when using silk-mediated dispersal

Agroecosystems are subject to regular disturbances that cause extinction or migration of much of their fauna, followed by recolonization from surrounding refuges. In small-sized aeronaut spiders, such recolonization is potentiated by their ability to rappel and balloon. These are complex behaviors that we hypothesized to be affected by neurotoxins, namely, neonicotinoids. We tested this hypothesis using two common farmland spider species, Oedothorax apicatus (Linyphiidae) and Phylloneta impressa (Theridiidae). The spiders were topically exposed by dorsal wet application or tarsal dry exposure to commercial neonicotinoid formulations Actara 25 WG, Biscaya 240 OD, Mospilan 20 SP and Confidor 200 OD at concentrations that are recommended for application in agriculture. Contact exposure to neonicotinoids suppressed the ability of spiders to produce the major ampullate fiber and anchor it to the substratum by piriform fibrils. Contact exposure to neonicotinoids also suppressed the ballooning behavior that was manifested by climbing to elevated places, adopting a tiptoe position and producing silk gossamer in the wind. Impaired ability of affected common farmland spiders to quickly recolonize disturbed agroecosystems by silk-mediated dispersal may explain their decline in multiple farmland ecosystems, in which neonicotinoids are applied.

Effect of Pesticides on Biological Control Potential of Neoscona theisi (Araneae: Araneidae)

The present study was designed to record the effect of λ-cyhalothrin, Bifenthrin, and Glyphosate on the mortality, avoidance behavior, foraging activity, and activity of Acetylcholine esterase (AChE) and Carboxylesterase (CarE) in Neoscona theisi (Walckenaer, 1841). Highest mortality (70%) in N. theisi was recorded against λ-cyhalothrin. However, Glyphosate was found to be least toxic. Spider spent less time on insecticides/herbicide-treated surfaces. Insecticides/herbicide-treated N. theisi consumed less prey than untreated control spiders. Similarly, when N. theisi were offered insecticide/herbicide-treated prey, they consumed significantly less. Increased AChE and CarE activities were recorded in insecticides/herbicide-treated spiders as compared to control group. Total protein contents were less in insecticides/herbicide-treated spiders than control group. The results revealed that λ-cyhalothrin is more harmful to spiders as compared to Bifenthrin and Glyphosate. It is suggested that the effect of all pesticides used in agro-ecosystem on beneficial insects should be evaluated before using them in the fields.