Biocontrol a possibile option to control manuka beetle (<i>Pyronota</i> spp) causing pasture damage on dairy farms on the West Coast

Abstract

Manuka beetle (Pyronota spp Bois Coleoptera Scarabaeidae) has often been reported causing pasture damage frequently in areas close to bush margins Larvae feed on the roots of pasture species producing damage that is often attributed to grass grub (Costelytra zealandica) During 200607 significant pasture damage was observed in dairy pastures established on flipped developments on sandy soils near Cape Foulwind and on hump and hollow developments near Bell Hill north of Lake Brunner Sampling revealed damage was caused by high populations of manuka beetle larvae; no grass grubs were found in either region The common manuka beetle Pyronota festiva was identified from both areas and a second Pyronota species (P edwardsi or P setosa) was found only on the sandy soils at Cape Foulwind A pathogen survey of Pyronota larvae from both regions showed very low levels of infection by bacterial and protozoan pathogens but did reveal moderate infection by the fungi Metarhizium and Beauveria in 3rd instar larvae A laboratory bioassay at 15C showed late third instar Pyronota spp larvae were susceptible to infection by Metarhizium anisopliae and Beauveria bassiana spores mixed into soil Further work will evaluate a promising local Beauveria brongniartii isolate as a biocontrol option against this emerging pest