The rôle of the host plant in the production of winged forms by two strains of the pea aphid, Acyrthosiphon pisum

Abstract

Aphids of both strains of Acyrthosiphon pisum can produce alate daughters after experiencing a controlled period of contact with other aphids. This response is maternal, embryos being irrevocably determined as apterae or alatae very shortly before birth. Females of the green strain crowded soon after the onset of parturition did not produce many alate offspring when reared exclusively on seedlings of the bean Vicia faba. When the insects fed on mature bean leaves after the 24 hr crowding treatment the proportion of alatae in their progenies was more than doubled. Besides being influenced by the diet imbibed after the crowding experience, the maternal response was conditioned by the host plant offered the test insects during their larval development. Bean seedling host plants decreased the proportion of alatae subsequently produced, while mature bean leaves had the reverse effect. The production of numerous alatae in response to the combined influence of crowding and a mature leaf host was rapidly halted when the parent aphids were transferred to bean seedlings. Often all larvae subsequently deposited became apterae. Aphids of the pink strain studied here were particularly sensitive to contact with other aphids, and readily produced large numbers of alatae even when feeding on bean seedlings. Nevertheless, more alatae appeared in the progenies of crowded females caged on mature bean leaves. Females of both strains reared singly on bean seedlings prior to the onset of parturition started to deposit alate daughters within 72 hr of being transferred without crowding to mature leaves. Progressively greater numbers of these forms were produced as larviposition continued. This response appeared earlier in the case of females reared singly on mature leaves from birth onwards. Two varieties of the pea Pisum sativum had a particularly pronounced effect on alata-production by females of the green strain. Regardless of whether the aphids imbibed sap from pea seedlings before or after a crowding treatment, the majority produced no alate progeny whatsoever. The response of the pink aphids was not as easily influenced by this factor. When previously crowded apterae of the green strain reproduced on mature pea leaves, a response developed of comparable intensity to that of insects confined on bean seedlings. Fewer alatae were produced by females caged on excised mature pea leaves fed with glucose and amino acids than on leaves fed with a pure glucose solution.