We previously reported that precocene caused the aphid Myzus persicae to produce male offspring, and further, that daughters (G1) of precocene-treated females also produced males in several temporal patterns. These patterns characteristically exhibited male production early in the reproductive sequence and/or approximately 10 days later. We suggested that ovulation of male eggs might occur at subthreshold juvenile hormone concentrations immediately after precocene treatment (i.e., during the late embryonic stages of the G1 aphids) and again in the last larval instar of the G1 aphids. This paper describes experiments in which G1 aphids were exposed to the JH analog kinoprene prenatally and in the last instar. It was shown that these treatments delayed, eliminated, or interrupted the expected sequences of males, thus providing evidence for the proposed scheme of male determination. The condition of the corpus allatum in G1 adults correlated with the pattern of male production; in continuous male producers the corpus allatum had undergone delayed destruction. A schematic model of the endocrine control of male determination is presented.