Abstract

Tasmanian grass grub, first recorded in Canterbury in 1920, is now well established in several areas of New Zealand. The adult beetles fly in January and lay their eggs in the soil after mating. After hatching, the larvae live in the soil and construct vertical tunnels from which they emerge at night to feed on and denude pasture plants. The effects of this pest on pasture were estimated by measuring pasture with larval densities ranging from 21-574 m². Larval infestation significantly reduced pasture mass in a linear fashion by around 5% per 100 larvae. For example, at one site from July to September, pasture mass Y = -0.816X + 1852, R2 = 0.3; where Y = pasture mass (kg DM per ha) and X = larvae per m². Losses in stock carrying capacities have been estimated to vary between 0.5 and 5 stock units per hectare depending on the farm carrying capacity and larval damage to pasture, resulting in losses of up to $315 per hectare.

MWA, Slay, and MW Fisher

Proceedings of the New Zealand Society of Animal Production, Volume 61, Christchurch, 13-15, 2001