Possible control of the melolonthid (Costelytra zealandica(White)) using transient insecticides against the adult

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Abstract To investigate the possible control of grass grub (Costelytra zealandica (White)) by applying insecticides at the time of adult emergence, the pattern of development of pupae and adults and of the appearance of eggs was determined on four sites in four successive years by soil sampling. Data on primary emergence of beetles were obtained on three of the sites and related to presence of eggs in the soil. Light-trap records showed that beetles were not generally trapped until quite old, and the appearance of numbers of beetles in the traps was too late in relation to primary emergence to be of value in timing insecticide treatments. Seventeen insecticides of low residue hazard were examined for contact activity against C. zealandica adults. The best of these were “Dursban”, Bayer 77488, and diazinon. Three field trials were conducted using these insecticides, two with ultra-low-volume and one with dilute spraying, each applied to plots within areas of infested pasture. DDT was also included in the high-volume spray trial. Up to four applications, each with rates of use up to 1 lb per acre, were made. Results, based on ensuing numbers of eggs and larvae in the plots, were all negative. It is suggested that the failure of treatments to exert any effect is associated with the behaviour of adult beetles, especially females, resulting in very limited contact with an insecticide deposit on the pasture surface. Unless ways of increasing this contact can be devised (e.g. by the use of attractants), it is concluded that this approach to control is not likely to be effective.