Mode of Host Selection by an Aphid

Abstract

CONCLUSIVE evidence of the properties of plants which determine host selection in aphids has been lacking¹. The host plants of the cabbage aphid, Brevicoryne brassicae (L), are restricted to the Cruciferae and Resedaceae² in which mustard oil glucosides are characteristically present³ and known to stimulate feeding by certain lepidopterous larvæ⁴. To test the effect of such a substance on B. brassicae, the mustard oil glucoside sinigrin was introduced into young leaves of the broad bean, Vicia faba L., which is not a host of this aphid. The leaves were set with the cut petiole in a 2 per cent aqueous solution of sinigrin for 2 h before and also during each experiment. Apterous virginoparous adult aphids were given a choice between such a sinigrin-treated leaf and a similar but untreated leaf, standing side by side under a 2 × 1 in. glass vial. 45 aphids were used in a total of five experiments. After 24 h an average of 93 per cent of the aphids were found settled and feeding on the sinigrin-treated leaf, with an average of four new-born larvae each. Only two larvæ altogether were found on untreated leaves and the few adults seen there were restless. B. brassicae were reared on sinigrin-impregnated broad bean leaves continuously to the fourth generation when the culture was still healthy.