Post-natal application of Precocene II (6,7-dimethoxy-2,2-dimethylchromene, PII) to newly-born pea aphid larvae, Acyrthosiphon pisurn (Harris), does not influence development and the PI1 promotion of winged progeny previously reported after pre-natal application appears to be exerted via a maternal control mechanism. The production of winged progeny by crowded, wingless adults can be inhibited by both pre-and post-natal application of Precocene Ill (6methoxy, 7-ethoxy-2,2-dimethyIchromene, PIII). Precocene Ill treatment also induces precocious adult development, i.e., early metamorphosis. Both wing inhibition and precocious metamorphosis were dose-and age-dependent when Plll was post-natally applied. Pre-natal application of juvenile hormone Ill or its agonist, pyriproxyfen, following treatment with PI1 or PIII, did not influence the precocene effects on wing induction or inhibition, respectively. Post-natal treatment with the juvenile hormone and pyriproxyfen, subsequent to PIII, reversed the precocious metamorphosis effect but not wing inhibition. This differential result, with an identical rescue protocol, suggests that Plll induction of precocious adult development arises as the result of the selective destruction of the corpus allatum cells and a lowered JH titre. However, the property of Plll that promotes the development of wingless forms appears unrelated to this decrease i n juvenile hormone titre.