Know thy enemy: non-sequenced based tool to identify species of manuka beetle and grass grub larvae

Manuka beetle (Pyronota festiva, Pyronota laeta, Pyronota setosa) and the New Zealand grass grub (Costelytra giveni) have overlapping distributions across parts of New Zealand as well as similar seasonal life cycles. Grass grub is the most damaging pasture pest in terms of economic losses while manuka beetle causes significant damage in key regions including the South Island’s West Coast and the North Island’s Central Plateau. Where manuka beetle and grass grub overlap, knowing which species is present in your pasture informs decisions about pest control. This has become even more important with the expansion of grass grub into coastal Buller, with potential for further spread and poses a new challenge to pastoral farmers in the region. Whilst it is possible to differentiate the larvae based on external morphology under a microscope, it requires entomological expertise and an expert eye. Here we outline a simple molecular method, based on restriction digestion of the mitochondrial cytochrome c oxidase subunit I (COI) gene, to facilitate the rapid identification and differentiation of C. giveni larvae from Pyronota species. The ability to differentiate these species in regions where they co-occur will assist with long-term management of these endemic pasture pests and allow studies investigating possible heterogeneity in the efficacy of biological control measures.