To explore the relationship between spiders and insects in agroecosytems, we ran two laboratory experiments to determine if pest insects reduced their foraging activity in the presence of spiders or cues left by spiders. First, we quantified the damage to soybean leaves [Glycine max L. (Merrill); Fabaceae] caused by Japanese beetles [Coleoptera; Scarabeidae; Popilliae japonica (Newman)] and Mexican bean beetles [Coleoptera; Coccinellidae; Epilachna varivestis (Mulsant)] in the presence of either the tangle weaver, Achaearanea tepidariorum (C.L. Koch) (Araneae; Theridiidae), or the orb weaver, Arigope trifasciata (Forskal) (Araneae; Araneidae). Although most beetles survived, they consumed less of the soybean leaf than the beetles in control containers with no spiders. In a second experiment, we attempted to determine if Japanese beetles responded to the cues (e.g., silk draglines and feces) left by three species of wolf spider [Araneae; Lycosidae: Pardosa milvina Hentz, Rabidosa rabida Walckenaer, and Hogna helluo (Walckenaer)] that differed in size and therefore in the risk they posed to the beetle. Wolf spiders were allowed to deposit cues in a container with a soybean leaf for 24 h. The spider was then removed, and a Japanese beetle was allowed to forage for an additional 24 h. Plant biomass was positively affected by cues from all three wolf spider species, but the strongest foraging response of the beetle occurred in the presence of cues from the largest wolf spider species. These results demonstrate that spiders can have an effect on plant production even if they do not consume herbivores directly, which can have important implications for biological control programs.
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Vol. 96 • No. 6