Juvenile hormone (JH) is critical for development, metamorphosis, and reproduction in insects. While the physiological importance of JH has been appreciated for decades, its biosynthetic pathway and molecular action remain poorly understood. Drosophila CG10527 encodes a protein with high homology to crustacean farnesoic acid methyltransferase (FAMeT) that converts farnesoic acid to methyl farnesoate (MF), a precursor of JH, but its in vivo functions remain unclear. Here we report that CG10527 is expressed widely in secondary cells in the male accessory glands, in ovarian follicle cells, and in glial cells in the nervous system. Furthermore, CG10527 is expressed abundantly in the corpora allata where JH is synthesized. To understand the physiological functions of CG10527, we generated specific CG10527 deletions. Phenotypic analysis showed that CG10527 null mutants are fully viable and fertile in both sexes, indicating that CC 10527 is not essential for survival and fertility. Surprisingly, CC 10527 mutants showed no defects in the biosynthesis of MF and JH. However, CG10527 mutants were 3-5 times more resistant than wild-type flies to topically applied MF and JH as well as the JH analog methoprene at both sub-lethal and lethal doses. Taken together, our data indicate that Drosophila CG10527 plays little, if any, role in JH biosynthesis but may participate in the JH signaling pathway. (C) 2010 Elsevier Inc. All rights reserved.