A range of insecticides, their formulations, rates of application, and method of distribution were tested. Carbofuran and isophenphos proved most effective, but control was poor (46-66% mortality in autumn trials). There was no difference between seed treatment and granular formulations although spraying high rates (6.0 kg a.i.z'ha) on to existing pasture proved effective. Results indicate that during winter-spring pasture production was related to larval population and that a population reduction of 1000 larvae/rn-is likely to produce an additional 156 kg DM/ha, i.e., in these trials a 3-10% growth response. Comparisons are made with other published data to support this suggestion.