Established Paropsis charybdis egg parasitoids are unlikely to control the newly invaded Paropsisterna cloelia (both Coleoptera: Chrysomelidae) in New Zealand

Abstract

The two egg parasitoids Enoggera nassaui (Girault) and Neopolycystus insectifurax Girault (both Hymenoptera: Pteromalidae) are biological control agents of the eucalyptus-defoliating paropsine leaf beetle Paropsis charybdis Stål (Coleoptera: Chrysomelidae), an invasive species in New Zealand. Recently another leaf beetle, Paropsisterna cloelia (Stål) (Coleoptera: Chrysomelidae), has established in New Zealand, causing defoliation on select eucalypt hosts, e.g., Eucalyptus bosistoana . To determine if established egg parasitoids can control Pst. cloelia , the host suitability and host preferences of the two parasitoids were tested under laboratory conditions and compared with in-field egg parasitism at a site where all parasitoid and beetle species were present. Laboratory and field assessments confirmed that both parasitoids can reproduce in P. charybdis and Pst. cloelia but have a strong preference for P. charybdis . Consequently, probabilities of unparasitized Pst. cloelia larvae hatching in the laboratory or field in the presence of either parasitoid was higher compared to P. charybdis , ranging between 32-79% versus 1-24%, respectively . Offspring of both parasitoids emerged 36% larger (wing length 1.40 mm versus 1.06 mm and 1.56 mm versus 1.07 mm for E. nassaui and N. insectifurax, respectively) from P. charybdis eggs versus Pst. cloelia eggs, confirming Pst. cloelia eggs as lower quality hosts for these parasitoids. We conclude that E. nassaui and N. insectifurax will not induce sufficient mortality in Pst. cloelia eggs to be effective biological control agents for this invasive beetle.

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