Biological Control of Paropsis charybdis Stål (Coleoptera: Chrysomelidae) and the Paropsine Threat to Eucalyptus in New Zealand
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Ineffective biological control of the Eucalyptus pest Paropsis charybdis Stål (Coleoptera: Chrysomelidae: Paropsini) in cold areas of New Zealand was believed to be caused a climatic mismatch of the egg parasitoid Enoggera nassaui Girault (Hymenoptera: Pteromalidae). Two Tasmanian strains of the parasitoid were introduced to test climate-matching theory in 2000, with approximately 7000 wasps released. Establishment of the Florentine Valley strain was detected in 2002 using the Mitochondrial (mtDNA) gene Cytochrome Oxidase I (COI) as a strain specific marker. The hyperparasitoid Baeoanusia albifunicle Girault (Hymenoptera: Encyrtidae) and primary parasitoid Neopolycystus insectifurax Girault (Hymenoptera: Pteromalidae) were detected for the first time in New Zealand. As paropsines have proven highly invasive internationally, a risk assessment of the paropsine threat to New Zealand was undertaken by evaluating the host range of E. nassaui and a reproductive assessment of 23 paropsine species in the genera Dicranosterna Motschulsky, Chrysophtharta Weise, Paropsis Olivier, Paropsisterna Motschulsky and Trachymela Weise. Enoggera nassaui proved polyphagous, but bioassay results proved that Paropsis species were significantly more susceptible to the egg parasitoid than Chrysophtharta species. Resistance within Chrysophtharta was attributed to spine-like chorion modifications. A COI derived Chrysophtharta phylogeny divided the genus into two distinct groupings, which was supported by chorion morphology. Paropsine reproductive output was tested for key parameters indicating pest potential. Pest species displayed fecundity exceeding 600 eggs at an oviposition rate above 10 eggs per day⁻¹. Several non-pest species were identified as potential pests based on these parameters. The Chrysophtharta phylogeny suggested a moderate relationship between genetic relatedness and reproductive output. The Acacia defoliating paropsine Dicranosterna semipunctata (Chapuis) was evaluated for its susceptibility to E. nassaui and reproductive output. Egg parasitism occurring in bioassay did not translate into biological suppression following a specifically targeted release of E. nassaui, and the fecundity and oviposition rates fell below the thresholds predicted for a pest paropsine species. Despite establishment of Tasmanian E. nassaui, hyperparasitism has now rendered this control agent ineffective in New Zealand. Neopolycystus insectifurax offers the best hope for future biological control of paropsine species in New Zealand.