Effects of population density on alienicolae of Aphis fabae Scop.: V. Variations in size, relative wing length and numbers of antennal sensorla of field alatae

SUMMARY Size, relative wing length and numbers of antennal sensoria of alate Aphis fabae caught in a suction trap 12.2 m above ground and of migrants, flyers and non‐flyers among alate A. fabae from field infestations on beans and beet are compared. The size of aphids in successive samples decreased throughout the period of colonization but, on average, beet aphids were bigger and broad bean aphids were smaller than field bean aphids. There were very few migrant alatae among the very large or the very small aphids from any of the crops, neither were aphids of these extreme sizes caught in the suction trap. Non‐flyers and beet aphids generally had relatively shorter wings than migrants and bean aphids respectively. The numbers of antennal sensoria differed more between aphids from the three crops than between classes of alatae from the same crop, although trap aphids, presumed to be migrating from field beans had more sensoria than alatae taken from that crop. The mean dry mass of flyers was usually less than that of migrants of a similar size, although if the mass of nymphs deposited before flight is added, it is apparent that a flyer would be heavier than a migrant of the same size at maturity. This additional mass is thought to be due to increased development of the embryos in the ovarioles of flyers at this time and indicative of their greater adaptation for reproduction.