TSUKIMURA, B.; LINDER, C.J.; NELSON, W.K.; California State University, Fresno; California State University, Fresno; California State University, Fresno: Ovarian Development Inhibition by Methyl Farnesoate in the Tadpole Shrimp, Triops longicaudatus

Methyl farnesoate (MF), a crustacean hormone, is an analog of Juvenile Hormone III (JHIII), a juvenilizing hormone in insects. This studied examined whether MF, which has been shown to inhibit adult metamorphosis in several crustacean species, acts as a juvenilizing hormone in the tadpole shrimp Triops longicaudatus . Oocyte production, performed exclusively by adults with mature gonads, was chosen as a parameter for measuring development. MF was administered to developing juveniles via aquatic vector (Artemia nauplii), and MF-coated shrimp pellets, and MF-liposome pellets. The Artemia were incubated in 30 μl of 5 μg/ml MF and fed to tadpole shrimp daily from hatching until day 10. MF-coated shrimp pellets were used in laboratory and rice field studies at 0.0001% and 0.001% MF concentrations by weight. Artemia vector and MF pellet feedings significantly reduced number of oocytes/brood weight in 5- and 10-day-old shrimp without affecting somatic growth. The 0.001% MF-coated pellet reduced the number of oocytes/brood weight, and also reduced somatic development as well, suggesting a toxic effect. At 0.001% MF-liposome pellets decreased ovary wt and concordantly, decreased the GSI. MF-coated pellets (0.0001% MF b/wt) administered to adults after day 5 caused no significant difference in brood weight from that of controls suggesting MF is a juvenilizing agent and not a gonad inhibitor. Barely detectable levels of MF have been detected in adult tadpole shrimp and thus, MF appears to inhibit ovarian development at physiological concentrations when administered to juveniles. This research was funded in part by the California Agricultural Technology Institute and California Rice Board.