Cold tolerance of overwintering third instar Plectris aliena (Coleoptera: Scarabaeidae) larvae

Plectris aliena is an invasive white grub that causes severe economic damage to the sweetpotato crop in southeastern North Carolina. The freezing point, or supercooling temperature, and effect of low temperatures on overwintering grubs were determined using surface contact thermometry. The freezing temperature of Plectris aliena third instar overwintering grubs was -5.3°C, verified by the appearance of an exotherm. Grubs were also exposed to low temperatures of -1.1°C, 1.7°C and 4.4°C in field soil with moistures of 0%, 4%, and 16% (determined gravimetrically) for 12, 24, and 72 hours (4 replications, n=108 grubs). Exposure to cold temperatures at various soil moistures and lengths of time had no effect on grub mortality after 7 days.