EVIDENCE FOR A POSSIBLE FITNESS TRADE-OFF BETWEEN INSECTICIDE RESISTANCE AND THE LOW-TEMPERATURE MOVEMENT THAT IS ESSENTIAL FOR SURVIVAL OFUK POPULATIONS OF MYZUS-PERSICAE (HEMIPTERA, APHIDIDAE)

Apterous aphids need to move from ageing to younger leaves in order to survive UK winters. This behaviour was studied at low temperatures in field and laboratory trials using Myzus persicae (Sulzer) clones repr esenting all five recognized categories of esterase-based insecticide resistance found in UK populations. Both studies showed that the tende ncy of aphids to move from deteriorating leaves was inversely related to their insecticide resistance level. This maladaptive behaviour asso ciated with greater insecticide resistance could lead to increased ris ks of aphids becoming separated from plants after leaf fall, and subse quent death from starvation when adverse cold and wet conditions preve nt return. Revertant clones, that had spontaneously lost extreme resis tance to insecticides by ceasing to express their amplified esterase g enes, tended to show similar behaviour to aphids that had retained the ir high resistance phenotypes. This implies that rates of movement wer e not related directly to esterase production.