Action of juvenile hormone mimics on the regulation of larval–adult and alary polymorphism in aphids

Abstract

IT has often been suggested that the development of the apterous and alate morphs of aphids is controlled by the corpus allatum (CA) and is therefore regulated by the same endocrine system that controls larval–adult development in monomorphic insects^1–6. Research on other polymorphic species, including the honey bee and termites, has shown that this function is compatible with the cyclical production of juvenile hormone (JH) during larval ecdyses as the morph-determining action of the hormone may be confined to a certain strictly defined critical period or may depend on specific hormone concentrations in the blood^7,8. In aphids the prenatal determination of late embryos as presumptive apterae has been attributed to high JH titres in the maternal haemolymph^4–6; and the subsequent realisation of the morph characters has also been thought to involve enhanced CA activity in the early instars of the developing larva^2,3. The evidence, which has been based on measurements of CA volume and on the effects of topically applied JH is nevertheless conflicting^9,10. The results reported here show that the intermediate and terminal forms produced by the application of juvenoids to developing alate aphids are unlike those resulting from authentic apterisation initiated either by the absence of crowding or by exposure to long photoperiods. This does not support the persuasive argument that the possession of certain apparently juvenile characters by the ‘neotinic’ apterae (for example, the wingless condition of the adult) is a reliable indicator of JH involvement.