Precocene II-induced alate production in isolated and crowded alate and apterous virginoparae of the aphid, Macrosiphum euphorbiae

Abstract

Precocene II was applied at doses ranging from 0.05 to 0.70 μg per individual to newly moulted adult alate and apterous virginoparae of Macrosiphum euphorbiae kept isolated or in groups of 10 per plant, under an 18L:6D photoperiodic regime. While isolated controls of both morphs produced exclusively apterous progeny, alatae virginoparae were produced in generally dose-dependent proportions by precocene-treated individuals. Grouped controls of both morphs produced alatiform progeny as expected, but in precocene—treated groups, the proportions of alate progeny generally increased as a function of dose. The overall proportions of alate offspring produced, and numbers of days after treatment when morph production was affected, were generally greater for alatae than for apterae, indicating a greater sensitivity to precocene in alatae. However during the first few days after treatment, the alatizing effect of precocene was stronger for apterae, suggesting that the first embryos produced by alatae were irreversibly determined as apterae. In an experiment where isolated alatae and apterae received 0.5 μg of precocene II at different ages ranging from 1 to 13 days after the adult moult, the alatizing effect of the compound, measured by the persistence of alate production, varied with age and morph. While in alatae, the persistence decreased more or less regularly with age, in apterae it initially increased to a maximum in the middle of reproductive life, and subsequently decreased. The results provide support for the hypothesis that juvenile hormone is involved in regulating alary dimorphism in M. euphorbiae.