Effect of conspecific and heterospecific feces on foraging and oviposition of two predatory ladybirds: Role of fecal cues in predator avoidance

Growing evidence suggests a flow of chemical information from higher to lower trophic levels that affects foraging and oviposition of 'prey' in response to potential risks from predators. This was investigated in two species of ladybird predators of aphids, Harmonia axyridis and Propylea japonica. H. axyridis is known to be the stronger intraguild predator and P. japonica to be the more frequent intraguild prey in interactions of these two species. These ladybirds share aphid prey on mugworts, hibiscus, and Italian ryegrasses in fields of northern Japan but largely avoid each other on the same plant. Fecal cues of these ladybird predators were found to contribute in their assessment of predation risk from conspecific and heterospecific competitors in common habitats. Gravid females of H. axyridis reduced rates of feeding and oviposition when exposed to feces of conspecifics, but not when exposed to feces of P. japonica. In contrast, gravid females of P. japonica reduced feeding and oviposition when exposed to feces of both H. axyridis and its own species. Females of both ladybird species exhibited similar behavior in response to water extracts of feces. For P. japonica, the influence of heterospecific feces was greater than that of conspecific feces. Our results demonstrate that feces of ladybirds contain odors that have the potential to deter the feeding and oviposition activities of conspecific as well as heterospecific ladybirds. Such deterrence allows these insects to avoid predation risk. Differences in responses of the two predators are discussed.