The distribution of third instar grass grub Costelytra zealandica (White) [Coleoptera: Scarabaeidae] in an agroforestry system: A dissertation submitted in partial fulfilment of the requirements for the Degree of Bachelor of Horticultural Science (Honours) at Lincoln University

Abstract

Population studies of the third instar grass grub larvae (Costelytrq zealandica) are reviewed against the background of changes in density in three replicated plots of perennial rye grass (Lolium perenne) and white clover (Trifolium repens) when grown in a Pinus radiata agroforestry system. Field sampling using stratified random methods for aggregated populations, found numbers were higher in the visibly damaged area, but were reduced in the area adjacent to it. There is a variability in the relationship between soil moisture and larval density. Larval densities were higher in the predominant windward side (facing south-west) than in the leeward side (facing north-east). Populations fluctuate in response to changes in soil moisture. Aerial photography is a technique used to record and measure areas of grass grub damage. An index using ground sampling estimations of population numbers and aerial photographic estimations of percentage damage gave variable results. A factor in the index was violated by the addition of the tree component.