Symposium: Prediction and monitoring of pest outbreaks Prediction of grass grub,<i>Costelytra zealandica</i>, (Coleoptera: Scarabaeidae) populations

Abstract

The sedentary nature of grass grub, Costelytra zealandica (White), infestations and the tendency for populations to increase steadily over several generations until they reach damaging levels allow populations over the build-up phase to be predicted with reasonable accuracy from the numbers present in the previous generation. Analysis of grass grub population densities from 3 areas of New Zealand showed that in the absence of catastrophic density-independent mortalities caused by adverse weather such as summer droughts, simple logarithmic regressions of the density in 1 generation (Nn + 1) against that in the previous generation (Nn) accounted for 80% of the variation in log Nn + 1, on average. Some consequences for the control of grass grub with insecticides are discussed.