Effects of phytochemicals on predatory decision making in a spider

Animals with small nervous systems may be prone to limitations in processing ability when confronted with a diversity of stimuli, especially if these involve multiple sensory modalities. We investigated the effect of the odour of the plant Lantana camara and its dominant volatile compound, β-caryophyllene, on the prey choice decisions of Evarcha culicivora, a jumping spider (Salticidae) that frequently visits L. camara as a site to mate and to obtain nectar. Evarcha culicivora expresses a strong preference for blood-fed female Anopheles mosquitoes as prey. We tested juvenile and adult E. culicivora in experiments involving live prey, lures made from dead prey and virtual prey, when presented with no odour, odour from L. camara and β-caryophyllene. We found that, in the presence of the plant-related odours, E. culicivora's prey preference was no longer expressed. This effect seems to be a consequence of the plant-related odours reducing the extent to which E. culicivora relies on a pre-attack pause and visual fixation routine (‘stationing’) when seeing prey. Stationing may be critical for adequate visual scanning, and thus correct identification of the prey, as we found that the longer the spider was stationed in front of prey before being subjected to a disruption, the more strongly E. culicivora expressed a preference for blood-fed female mosquitoes. This seems to be an unusual example of a specific modulation of visually based prey choice behaviour being mediated by an environmental chemical cue not pertinent to the prey.