Epoxidation of juvenile hormone was a key innovation improving insect reproductive fitness

Methyl farnesoate (MF) plays hormonal regulatory roles in crustaceans. An epoxidated form of MF, known as juvenile hormone (JH), controls metamorphosis and stimulates reproduction in insects. To address the evolutionary significance of MF epoxidation, we generated mosquitoes completely lacking either of the two enzymes that catalyze the last steps of MF/JH biosynthesis and epoxidation, respectively: the JH acid methyltransferase (JHAMT) and the P450 epoxidase CYP15 (EPDX). jhamt(-/-) larvae lacking both MF and JH died at the onset of metamorphosis. Strikingly, epox(-/-) mutants, which synthesized MF but no 1H, completed the entire life cycle. While epox(-/-) adults were fertile, the reproductive performance of both sexes was dramatically reduced. Our results suggest that although MF can substitute for the absence of JH in mosquitoes, it is with a significant fitness cost. We propose that MF can fulfill most roles of JH, but its epoxidation to JH was a key innovation providing insects with a reproductive advantage.

Automated summary

The study showed that while MF can substitute for JH in mosquitoes, it comes with a significant fitness cost, highlighting the importance of epoxidation to JH for insect reproduction.