The colonization by Cavariella aegopodii Scop, of carrot plants of different sizes

During a study of the biology of Cavariella aegopodii Scop. (Dunn, 1965) aspects of the role of this aphid as a virus vector have been investigated each year by briefly exposing a succession of potted carrot plants in the field to the incoming winged forms of the aphid (Dunn & Kempton, 1966). Generally fifty plants of each of two different heights, within a range of 1–5 in, have been exposed simultaneously and when the alate C. aegopodii on these have been counted 3–4 days later, the aphid appeared always to have been differentially attracted to the larger plants. This seemed unlikely to be true, however, because as a crop young carrots suffer more severely from this pest than carrots which are a few weeks older, but for some years the aphid was not abundant enough for the situation to be investigated.