Soil distribution of Noxia canegrubs and the effect of plough-out on numbers

Noxia canegrub, Lepidiota /loxia Britton, is a pest of sugarcane in southern Queensland and was first identified in 1983. The soil profile distribution of third instar larvae was studied at Bundaberg for 7 months from August 1993. Larvae were aggregated in the row throughout the sampling period, and at depths of 10-30 cm until mid-spring when vertical distribution in the soil profile became more uniform. Larvae lost weight and suffered 65% mortality between late wmter and pupation in the following autumn. Plough-out reduced numbers by 76%; a bare fallow maintained by herbicide application reduced grub numbers by 45% after 8 weeks, while an additional 60% mortality occurred independently of treatment effects. This mortality was probably due to predation by White Ibis (Threskiornis molucca) to starvation and to disease. The practical value of plough-out and bare fallow for canegrub control is discussed.