Effects of extended and repeated exposures to low temperature on mortality of the peach-potato aphid Myzus persicae

1. The survival of adult and first-instar Myzus persicae reared at 20-degrees-C and 10-degrees-C was investigated after brief (1 min) exposure in the absence of plant material to temperatures between -5-degrees-C and -25-degrees-C, and extended exposures on plants of 1-10 days at a constant 5-degrees-C, 3-degrees-C and -5-degrees-C and a 24 h cycling regime between 5-degrees-C (18 h) and -5-degrees-C (6h). 2. Life stage, rearing temperature, period of exposure and temperature regime all had a significant effect on the ability of aphids to survive cold. The effects of life stage and rearing temperature were most noticeable following exposure to cycling temperatures and extended exposures at -5-degrees-C, and least apparent after 1 min exposures at lower sub-zero temperatures. 3. Mortality following exposure to temperatures cycling between -5-degrees-C and 5-degrees-C was greater than that at 3-degrees-C (the mean of the cycling temperatures) and less than at a constant -5-degrees-C, suggesting that when temperatures fluctuate by a few degrees around 0-degrees-C the minimum temperature may affect survival to a greater extent than the mean. 4. These results suggest that an overwintering population of acclimated M. persicae would persist without significant mortality after a period of 7-10 days with -5-degrees-C frosts each night.