HOST FINDING BY APHIDS IN THE FIELD: GYNOPARAE OF MYZUS PERSICAE (SULZER)

Attempts to test experimentally the theory of olfactory attraction to host plants gave negative results, and more conclusive evidence was sought by recording the behaviour of host-finding migrants in the field. The first of three occasions when the natural alighting rate was high enough for comparative purposes was an autumn migration dominated by Myzus persicae returning to its specific overwintering host, the peach tree.
The proportion of M. persicae gynoparae among all aphids caught alighting on a spindle tree, where persicae does not overwinter, was as high as on peach. The much heavier accumulation of migrants on the peach was evidently due, not to their differential alightment, but to their differential rate of departure, with a longer average stay on the peach. The proportion of persicae gynoparae was smaller in catches on transparent sticky traps than among alighters on the trees, and they avoided alighting on brussels sprout plants more often than on peach. Only a fraction of those that approached the plants alighted, even on peach; and only a small fraction of those that did alight, stayed, even on peach.
There was appreciable colonization of spindle and sprouts by the M. persicae gynoparae and some 'wasted' oviposition by their progeny on spindle. After the migration was over the peach leaves entered the last stages of senescence before the spindle leaves, and persicae gynoparae (no longer able to fly) that were given access to both at that time, settled preferentially on spindle. The distribution of males created the impression that they were less host-specific than gynoparae.