Attraction of a predator to chemical information related to nonprey: when can it be adaptive?

Information specificity can be important to animals in making optimal decisions. However, it is not always necessary to use every level of specificity. We analyzed the response of the predatory mite Phytoseiulus persimilis to plant-produced information related to a nonprey herbivore. This predator is a specialist feeding on spider mites in the genus Tetranychus. Caterpillars of Spodoptera exigua cannot serve as prey. Plants respond to an infestation by herbivores with the emission of volatiles that attract carnivorous enemies of the herbivores. Conspecific plants infested with different herbivore species can emit blends that are qualitatively identical, while differing in the ratios of blend components. However, different plant species emit volatile blends that differ qualitatively. We demonstrated that the predator P. persimilis is attracted to volatiles from bean plants infested with S. exigua caterpillars, but that this attraction is affected by predator starvation and host-plant experience. One-hour and 24-h starved predators were made to represent predators that just lost a prey patch versus predators that have totally lost a prey patch. Predators reared on spider mites on bean were attracted to bean plants infested with caterpillars when starved for 1 h but not when starved for 24 h. Both predator groups were attracted to bean plants infested with prey (i.e., spider mites). One-hour starved predators can use the odor to relocate the rewarding prey patch they just lost contact with, and using a general olfactory representation of the blend is sufficient for relocation. In contrast, for 24-h starved predators, the perception of a plant's odor blend is unlikely to represent the prey patch lost, and discriminating between an odor blend representing prey or nonprey will avoid investing time in finding a nonprey herbivore. In contrast, predators that had been reared on spider mites on cucumber and thus had experienced a qualitatively different odor blend were not attracted to volatiles from caterpillar-infested bean plants. They were attracted to spider mite-infested bean plants, irrespective of starvation level. To cucumber-experienced predators, the perception of bean plant odor cannot represent the prey patch lost, but only a new prey patch. Being discriminative and only responding to prey-infested plants is adaptive in this situation. Our results are discussed in the context of optimal information processing.