Seasonal changes in distribution of Childers canegrubs, Antitrogus parvulus Britton, in the soil profile

Damage to sugarcane in the Bundabergregion appears during sprihg and summer as a result of feeding by third instar Childers canegrubs (Antitragus parvuius Britton). In a widely accepted scenario third instars migrate down the soil profile to overwinter and return to the surface in spring. Two sites were sampled at monthly intervals for a year and it was found that during winter third instars remained near the surface in considerable numbers at one site but increasingly moved deeper at the second site. There was no consistent relationship between position in the soil profile and mean temperature and soil moisture for the previous week measured at 10 and 40 cm. Rearing field collected larvae to adulthood revealed that third instars that remained near the surface during winter generally differed in age by 12 months to those found deep in the soil. The author concludes that movement down the soil profile is dependent on reaching the physiological age necessary for moulting to the next stage. The implications for sampling and treatment of Childers canegrubs are discussed.