Movement by mating females of a host alternating aphid: a response to leaf fall

Autumn remigrants of the host alternating bird cherry-oat aphid, Rhopalosiphum padi, colonise individual plants of the winter host, Prunus padus. However, they do not select leaves at different stages of senescence, which is surprising as leaf fall is a definitive deadline for production and development of mating females. For successful development mating females should be mobile and have the capacity to evaluate leaf senescence. Although remigrants do not selectively colonise leaves at different stages of senescence, mating females were found in very low numbers on leaves that were about to be shed. In choice test and olfactometer bioassays, abscising leaves were avoided by mating females. In the field mature leaves were available for colonisation during the period of leaf fall of P. padus. We conclude that mating Females abandon abscising leaves in favour of leaves at an earlier stage of senescence, increasing the time available for mating. Our results support the role of remigrants as pioneers which identify good winter host plants, and of mating Females as mobile searchers for optimal feeding and mating sites.