Many insecticides kill both target and non-target species by affecting specific sites within the nervous system. Since an animal's behavior is governed by interactions among nerve cells, it is not surprising that even low doses of pesticides influence behavior. While most research on sublethal doses of pesticides has concentrated on the economically-important insect pests (Haynes 1988), few studies have assayed the effects on this aspect of spider biology. This is surprising given that spiders are known to reduce and regulate insect species for several key crops (Clark & Grant 1968; Luczak 1979; Mansour et.al. 1980; Mansour, Rosen & Shulov 1981; Nyffeler, Riechert & Lockley 1984; Winfield, Dean, & El-Salam 1992; Young & Edwards 1990). However, many insecticides used to control insect pests may also affect spider populations either directly (through death) or indirectly (changes in behavior or physiology). Given the likely importance of spiders in insect control, researchers have evaluated pesticide toxicity for various spider species. In one major study the susceptibility of several spiders to 30 pesticides was tested. Toxicity ranged from no mortality (biological compounds, herbicides, fungicides) to medium mortality (pyrethrins, organophosphates, catbamates), and high toxicity (cyclo compounds; Mansour & Nentwig 1988). Other studies have suggested that many insecticides have little effect on spider population densities (Hilburn & Jennings 1988; Riechert & Lockley 1984; VanDenBerg, et.al. 1990) and have led IPM researchers to rate the environmental risk of many pesticides to beneficial arthropods, including spiders, as low (Higley & Wintersteen 1992). Recent research, however, has shown that even sublethal doses of insecticides adversely affect insect (Haynes 1988) and arachnid species (Chu, Hor & Chen 1976; Chu, et.al. 1977; Samu and Vollrath 1992).
You can see a powerpoint presentation reviewing some of the research outlined here by clicking here. This presentation was given as a poster presentation at the 2000 meeting of the American Arachnological Society.