The effects of spider cues on Colorado Potato Beetles (Leptinotarsa decemlineata)
Colorado potato beetles, Leptinotarsa decemlineata, are chemically-protected crop pests on economically important solanaceous plants. We measured predation on potato beetles by four species of spider: the crab spider, Misumenoides formipes, the long-jawed orb weaver, Tetragnatha laboriosa, and the wolf spiders, Hogna helluo and Pardosa milvina. We also measured leaf damage on eggplants, Solanum melongena, in the presence of two of the four spider species (H. helluo & P. milvina) as well as leaf preference or avoidance for leaves previously walked on by one of the four spider species for 24 h. We found no predation on beetles by any of the four species of spider during a 4 h test period (n = 24/spider species). We found significant reductions in herbivory in the presence of Hogna helluo but not the smaller wolf spider, Pardosa milvina (n = 48/spider species). When given a simultaneous choice between eggplant leaves with spider cues and those without, beetles showed a significant initial avoidance for leaves previously occupied by H. helluo, but beetles showed no significant initial avoidance of spider-cued leaves of any of the other three spider species (n = 48/spider species). In the absence of live spiders, beetles showed significantly lower herbivory levels on leaves previously occupied by H. helluo, P. milvina, or T. laboriosa, compared to leaves without spider cues, but beetles showed no reduction in herbivory on leaves previously occupied by M. formipes (n = 48/spider species). Our results suggest that even chemically-protected herbivores show reduced feeding in the presence of some generalist predators and that chemical cues from predators (silk and excreta) may also reduce herbivory even when these predators present no predation risk.