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

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. We did double-blind experiments over three breeding seasons in which wild-caught females were treated with water, acetone, 100, 500, or 1000 µg of methoprene dissolved in acetone, maintained in cages for 2–4 days, and then either killed and dissected or maintained in the lab until the majority had died naturally. We predicted that acetone would have no effect and that methoprene treatment would increase ovarian development. Surprisingly, the total volume of the three largest oocytes (ODVol3) was higher in acetone-treated females than in those treated with water, suggesting that acetone may promote vitellogenin production. Methoprene treatment resulted in additional increases in ovarian development, especially ODVol3, suggesting that acetone and methoprene together have additive effects. No significant differences in survival were observed amongst 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.