Witnessing predation can affect strength of counterattack in phytoseiids with ontogenetic predator–prey role reversal

Predators are usually larger than their prey, but because size changes during ontogeny, predator and prey roles may be reversed. Hence, an individual may be prey when juvenile, but as an adult, it may counterattack the juveniles of its childhood enemy. Earlier, we showed that juvenile predatory mites, Iphiseius degenerans, recognize adults of another predatory mite species that attacked and killed conspecifics of the juveniles. Upon becoming adult, these former juveniles showed an increase in attacks on juveniles of their enemy. Here, we tested whether adult females of I. degenerans show a similar response after witnessing attack on conspecific juveniles in the presence of suitable alternative food (i.e. pollen). We used three predatory mite species involved in reciprocal intraguild predation. We found mixed results: the rate of attack on juveniles of one species of predator, Neoseiulus cucumeris, did increase after witnessing the killing of conspecific juveniles, but the rate of attack on juveniles of another species, Amblyseius swirskii, did not increase after such an experience. Furthermore, we found no conclusive evidence for species-specific antipredator responses. It is unlikely that cues of previous predation events affected the behaviour of adult predatory mites, because the trials were conducted on new experimental arenas free of predation cues. We conclude that adult predatory mites can change their antipredator behaviour in response to having witnessed predation on vulnerable juvenile conspecifics.