Differential susceptibility in a specialised aphidophagous ladybird, Platynaspis luteorubra (Coleoptera: Coccinellidae), facing intraguild predation by exotic and native generalist predators

The establishment of exotic generalist predators raises concern about possible domination of the invaded community and displacement of native species. In this respect, recent studies suggest that specialists are likely to be more at risk of niche displacement than generalists, thereby compromising biological control in agroecosystems. Under laboratory conditions, we examined the susceptibility of a specialised myrmecophilous ladybird, Platynaspis luteorubra Goeze, as intraguild (IG) prey of generalist native (Oenopia conglobata L. and Adalia bipunctata L.) and exotic (Harmonia axyridis Pallas) coccinellid species. We described parameters of predatory behaviour (for example, attack rate and effectiveness of antipredator defence) and their variation among predators. Furthermore, we estimated the effect of these parameters on the time to predation using a Cox proportional hazards model. We found that A. bipunctata was the most effective IG predator of P. luteorubra, with the highest rate of successful attacks; however, P. luteorubra was not very susceptibile to attack by O. conglobata or H. axyridis, and these species exhibited lower rates of successful attack and predation. Our results, together with field observations, suggest that IG predation is a factor that fosters niche specialization in P. luteorubra and decreases the realised niche of this species in central Italy. Furthermore the lower susceptibility of P. luteorubra to H. axyridis may be due to a lack of historical co-occurrence between preimmaginal stages, possibly arising from differental selection of oviposition sites.