Direct and indirect cues of predation risk influence behavior and reproduction of prey: a case for acarine interactions

Little is known about the flow of chemical information fromhigher to lowerlevels within the animal food chain. However,this information may determinethe behavior and distributionof many animals (e.g., that of potential prey)when exposedto direct and indirect cues of predation risk. We usedherbivorousspider mites, Tetranychus urticae Koch (Tetranychidae) asamodel to examine the foraging and oviposition decisions thatprey make whenexposed to these cues. We conducted laboratorytests to determine if theprevious presence of predators (directcues) on leaf discs or the presence ofinjured conspecifics(indirect cues) alters the distribution of adults andeggs ofT. urticae. When given a choice, after 24 h, fewer adults andeggswere found on leaf discs that had previously contained specialistspidermite predators, Phytoseiulus persimilis Athias-Henriot(Phytoseiidae),than on discs unexposed to predators. Also, more T.urticaeemigrated from predator-exposed discs than from unexposed discsorfrom those that had previously contained nonpredatory mites(Tyrophagusputrescentiae, Acaridae). Finally, fewer T. urticaeforaged andlaid eggs on predator-exposed discs or on thosewith artificially damagedconspecifics (eggs or dead adults)than on discs with intact conspecifics.Tetranychus urticaeprobably recognizes infochemicals (kairomones)from its predatorsor cues from injured spider mites and consequently avoidsfeedingor ovipositing in areas exposed to these cues. Recognition andavoidanceof kairomones from specialist predators by this prey are likelytobe hereditary, but avoidance of injured conspecifics maybe an adaptation toavoid predators that are not inherentlyrecognized. We discuss the behavioraland ecological implicationsof our findings.