LINDER, C.J.; TSUKIMURA, B.*: Inhibitory effects of methyl farnesoate (MF) on the reproductive development of tadpole shrimp (TS), Triops longicaudatus

To identify a reproductive regulator for the invasive TS, T. longicaudatus, the hormone MF was administered to growing juveniles. To administer MF, aquatic vectors (Artemia nauplii) incubated in 0.05% albumin and 5 �g/ml MF for 2 hours, were fed to TS daily from hatching until 10 days of development. Oocyte development was observed by dissection at days 5 and 10. Body cavity examination of day 5 TS was a mean of 33.2 oocytes in the controls and 16.5 in the MF treated (p<0.002, ANOVA). Day 10 ovarian weight was reduced from a mean of 1.1 mg (controls) to 0.6 mg (MF treated) (p<0.01, ANOVA). There were no somatic effects (body weights and lengths) between control and treatment groups at day 5 or 10. To study efficacy in rice fields, MF was added to shrimp pellets with Tween-20 as a binding solution at two treatment concentrations [low-0.0001% = 1 mg MF/kg pellets (MF1) and high-0.001% = 10 mg MF/kg pellets (MF2)]. Initial lab tests of the pellets indicated the number of oocytes for MF1 treated TS at day 5 were reduced from the controls (p<0.045, ANOVA). At day 10, ovary weight also decreased (p<0.01, ANOVA), with no somatic differences. The MF2 treatment at days 5 and 10 resulted in differences in body weight, body length, # of oocytes and ovarian weight, indicating a possible toxic effect. A random block design of 16 rings was set in a rice field to study the MF1 and MF2 pellet treatments. At day 5, MF1 and MF2 treatments decreased both ovary weight and GSI. No somatic effects were detected with MF1, however toxic effects were possible in MF2. At day 10, significant block effects obscured any MF effects. MF appears to inhibit ovarian development when administered to juveniles.