Respiration and Behavior of a Sugarcane Grub, Ligyrus Subtropicus (Coleoptera: Scarabaeidae) Under Flooded Conditions

The sugarcane grub, Ligyrus subtropicus (Blatchley) encounters both natural field flooding and controlled field flooding by Florida sugarcane growers. Third instar larvae (grubs) of L. subtropicus were tested in various flood tests. After a five day (120 h) simulated flood, 68% of grubs survived at 18° C versus 0% at 28° C. Respiration as indicated by CO2 production was significantly higher in grubs at 28° C in both flooded and unflooded treatments than in grubs at 18°C under similar conditions. These data indicate that grubs drown faster at higher temperatures at least partly due to increased respiration. In behavior tests conducted at water temperatures of ca. 24° - 25°C, grub populations moved upward in response to flooded conditions including 21.7% of the grubs which emerged from the soil to settle on the soil surface. Grubs became sluggish after 2 h underwater. Within 24 h underwater, all grubs were comatose (non-responsive to probing) and remained in this condition until death.