Effect of a juvenile hormone analogue (methoprene) on ovarian development and survival in the Eastern Carpenter Bee (Xylocopa virginica)

Abstract

Differences in opportunities to lay eggs, and thus differences in extent of ovarian development, underlie reproductive hierarchies in social insects. In most insects, ovarian development is regulated by juvenile hormone (JH), so differences in reproduction are predicted to be proximately regulated by JH. We investigated the impact of a JH analogue, methoprene, on ovarian development and survival in Xylocopa virginica, a facultatively social carpenter bee in which social females form linear dominance hierarchies quite different from eusocial societies. Our objectives were twofold: to evaluate variation in the ovarian status of potential breeders throughout the brood-producing phase of the colony cycle, and to investigate the extent to which methoprene treatment would increase ovarian development. We used a double-blind experiment in which wild-caught females were treated with 0, 100, 500, or 1000 µg of methoprene, maintained in cages for two to four days, and then either? killed and dissected or maintained in the lab until the majority had died naturally. Control females exhibited a distinct seasonal pattern in which ovarian development increased through the first part of the brood-provisioning phase to a peak in weeks 7 and 8 (mid-June), then subsequently declined, as brood production ceased. Methoprene treatment resulted in a dose-dependent increase in ovarian development, primarily affecting the volume of mature oocytes, but having no effect on the total number of developing oocytes. The effects of methoprene were observed within two days of treatment, suggesting rapid hormonal modulation of ovarian development. No significant differences in survival were observed among bees treated with varying dosages of methoprene, indicating the absence of adverse effects on bee health and activity. Our results support the predicted gonadotropic effects of methoprene in X. virginica, enabling future studies to explore JH influence on reproductive dominance within linear reproductive hierarchies.