Inundative release of coccinellid beetles into eucalypt plantations for biological control of chrysomelid leaf beetles

1. Inundative augmentative releases of adult coccinellid beetles were assessed for their potential to effectively supplement biological control of outbreak populations of the Eucalyptus leaf beetle Chrysophtharta bimaculata in Eucalyptus nitens plantations. 2. Mixed groups of two species of overwintering coccinellids, Cleobora mellyi and Harmonia conformis, were collected from the field then fed three diets in the laboratory prior to release. Both species were released in the summer into two E. nitens plantations with economically damaging Chrysophtharta populations. 3. Differences between dispersal of coccinellids fed the three diets were slight; beetles brought straight out of overwintering before release were initially slower moving onto trees. 4. Numbers of coccinellids on trees in monitoring plots decreased exponentially with time, and populations had returned to prerelease levels 7 days after release. The number of coccinellids recaptured decreased with increasing distance from the release point with very few coccinellids per tree at 70 m distance. Dispersal of C. mellyi away from the release plot was slower than that of H. conformis. 5. Numbers of coccinellids on trees were significantly related to predation levels of C. bimaculata with a large decrease in the C. bimaculata population to below the economic damage threshold in plots where the numbers of coccinellids were high. 6. The results of this study suggest that inundative release of laboratory reared coccinellids is possible for biological control of C. bimaculata, although it may only be economically viable in small, environmentally sensitive areas.