Low temperature mortality of the peach‐potato aphid Myzus persicae

ABSTRACT. The mean supercooling points of first instar and adult Myzus persicae (Sulzer) maintained at 20°C and cooled at 1°C min −1 were −26.6 and −25.0°C respectively. The LT 50 (temperature) of the same age groups drawn from the same population and cooled at the same rate were −8.1 and −6.9°C, indicating extensive pre‐freeze mortality in M.persicae under laboratory conditions. Acclimation at 10 and 5°C did not affect supercooling but depressed the LT 50 of both first instars and adult aphids. Freezing of leaves during feeding did not increase mortality above that expected from the direct effects of low temperature. The level of cold in different winters can be expressed in terms of the total number of frost days, and the frequency of abnormally cold days. Winter temperatures differ markedly in a vertical profile from the soil to the soil or grass surface, and then to the air (and foliage) above. The time of the first record of M.persicae in suction trap samples is correlated with January and February temperatures except in the west of England and Wales. Further north December and January temperatures are relatively more important. Winter temperatures and the resultant aphid mortality is a primary determinant of the timing of the spring migration.