Reproduction in moths and butterflies is a dynamic process that is influenced by various endogenous physiological processes and exogenous factors. The Lepidoptera may be divided into four distinct groups based on their gonadotropic hormones and other reproductive and biological characteristics, regardless of phylogenetic relationships. Some species have integrated their reproduction tightly with the endocrine events of metamorphosis, the waxing or waning ecdysteroid levels. Other species rely instead on juvenile hormone (JH), in part or solely. Species of Lepidoptera that rely on JH as the gonadotropic signal also exhibit polyandry. Several mechanisms have been suggested for the occurrence of polyandry, including availability of male-transferred nutrients (gonadotrophic effect), need for additional sperm, and increased genetic variability. We propose an additional reason for polyandry observed in some lepidopterans. If a female remains a virgin, her endogenous gonadotropic signal diminishes, and eggs that have been produced already may be resorbed to increase longevity. During copulation, the male may trigger a neural/humoral response in the female, thus stimulating release of her endogenous gonadotropic signal, JH, and/or inhibiting degradation of the same, whence she matures new eggs. The mating effect appears to act humorally on the cephalic structures in several species. Whether this change in JH titer is due to an effect on synthesis and release by corpora allata only or occurs in conjunction with inhibition of JH degradation is unknown. Arch. Insect Biochem. Physiol. 35:539–558, 1997. © 1997 Wiley-Liss, Inc.