SEXUAL FORMS OF THE PEA APHID, ACYRTHOSIPHON PISUM, PRODUCED ON AN ARTIFICIAL DIET

Abstract

In recent years a number of aphid species have been successfully reared on chemically defined diets (Dadd & Mittler, 1966; Auclair, 1965; Dadd & Krieger, 1967; Ehrhardt, 1968). The development of such diets has offered an opportunity to study in detail several aspects of the physiology of these insects. In particular, the composition of the artificial diet has been shown to influence the production of winged forms by Myzus persicae (Sulzer) (Mittler & Dadd, 1966; Dadd, 1968). In all studies thus far, the aphids have been maintained in the parthenogenetic condition in order to accumulate data concerning the growth and fecundity of females of successive generations. However, it was clearly of interest to determine whether sexual forms could be produced by diet‐reared aphids. If so, further information regarding the sexual reproduction of these insects would be forthcoming.Attempts to achieve this using local strains of Myzus persicae, Aphis fabae Scopoli and Acyrthosiphon pisum (Harris) were unsuccessful, presumably because these strains were anholocyclie (Kunkel, unpubl.). A clone of a green strain of A. pisum, previously found to be holocyclic (Sutherland, unpubl.), was then obtained from England and was cultured at 20° C in a photoperiodic regime of 16 hr light: 8 hr dark per day on young bean plants (Vicia faba). The artificial diet on which the experimental aphids were maintained was formulated according to Dadd (1967) and enclosed in sachets of stretched parafilm (Dadd, Krieger & Mittler, 1967). The aphids were provided with fresh sachets every 3–4 days.Adult apterous females taken from the plant culture were caged in groups of five, and exposed to a photoperiodic regime of 10 hr light: 14 hr dark per day at 15°. Successive batches of larvae deposited by these aphids were maintained in this environment until they were adult and had produced offspring for several days. These developed into oviparae and males. Compared to the sexual forms produced on host plants, these diet‐reared individuals grew relatively poorly and mortality was high. Nevertheless, the surviving oviparae deposited numerous eggs, but these remained pale green whereas viable, fertilized eggs deposited by plant‐reared oviparae rapidly become black.In the case of aphids reared on host plants in a short‐day environment the possibility exists that the photoperiod may act indirectly via the plants and not directly on the insects themselves — a doubt which has been raised concerning Megoura viciae Buckton (von Dehn, 1967). However, our results with A. pisum reared on artificial diet demonstrate, as Lees did for M. viciae (Lees, 1960, 1967), that it is unnecessary to implicate the host plant in the determination of males and oviparae. This does not, of course, exclude the possibility that photoperiod‐induced changes in a host plant may play a role as well. Nor have we ruled out the possibility that dietary composition may influence the aphids directly or their response to other environmental stimuli leading to the production of sexual forms.