Intraguild predation and prey preferences influence biological control of Paropsis charybdis by the southern ladybird, Cleobora mellyi

Intraguild predation is common in most ecosystems and has the potential to disrupt biological control. Coccinellids are widely used biological control agents that often engage in intraguild predation against parasitoids of their shared prey/hosts. The eucalypt pest Paropsis charybdis is the target of several biological control agents: a coccinellid, Cleobora mellyi, and two egg parasitoids, Enoggera nassaui and Neopolycystus insectifurax. Parasitised P. charybdis eggs are slower to develop than unparasitised eggs so parasitised eggs remain exposed to predators for longer. The potential for intraguild predation by C. mellyi to interfere with biological control of P. charybdis by its egg parasitoids was investigated. A series of choice tests demonstrated that C. mellyi adults and larvae have strong preferences for unparasitised P. charybdis eggs over parasitised, irrespective of parasitoid species. Adult and larval C. mellyi also fed readily on acacia and eucalypt psyllids with some evidence of preference for these prey over unparasitised P. charybdis eggs. A sole diet of P. charybdis eggs is sufficient for C. mellyi to complete development but is not enough to support reproduction unless supplemented with psyllids. These prey preferences for unparasitised over parasitised eggs, taken together with the necessity of psyllid prey for reproduction, reduce the likelihood that C. mellyi will disrupt biological control of P. charybdis.