Key factors in control of Greyback Canegrub populations : SRDC final report BS120S

Abstract

Greyback canegrub outbreaks with severe losses in sugar production have persisted for more than six years in the Burdekin district, but population densities of the pest have declined at locations in the Herbert Valley, Tully and Innisfail districts over the same period. Six species of pathogenic organism were found to cause disease and death of greyback canegrubs, with relatively high incidence in grubs collected from the Herbert Valley, Tully and Innisfail study sites, but low incidence in the Burdekin. No deaths from entomopathogenic diseases were recorded in 226 grubs examined from the Burdekin in 1998. Two microorganisms, Adelina sp (Protozoa: Coccidia), and Metarhizium anisopliae (Deuteromycetes fungi), were the most prevalent pathogens in far north Queensland grub populations. Incidence of Adelina sp. alone accounted for 55-64 % of the variance in mortality of grubs recorded from samples collected across all locations in 1994 and 1995. The initial objectives of this SRDC funded study were to study dispersion of greyback canegrubs in the soil profile and devise a sampling program to estimate population density with known precision; monitor population density of greyback adults, eggs and larvae; identify mortality factors which act on each life stage including climate, natural enemies and farming practices; determine key factors which control greyback population changes and suggest ways to suppress population growth; develop model which predicts changes in greyback populations. Following a review in April 1995 the project was expanded to encompass the following additional objectives; assess the effects of crop management strategies on frequency of occurrence of diseases in greyback canegrubs; demonstrate pathogenicity of selected microorganisms to greyback grubs; determine dose/response relationships (ie infectious dose, time to death, effects on larval feeding and growth); attempt small-scale in vitro culture of selected microorganisms which display pathogenicity to grubs.