TUBERTY, S.R.: Effects of the insect juvenile hormone agonist, methoprene, on female growth and reproduction in the Gulf sand fiddler crab, Uca panacea.

Adult Uca panacea were distributed randomly (250 females, 100 males per pond) into six estuarine ponds in order to determine the effects of field applications of methoprene (Altosid� XR briquets) on female growth and reproduction. Duplicate reference ponds, low-dose ponds, and high-dose ponds (maximum labeled application) were utilized. Monthly sub-samples were collected by pitfall trapping May – October, 2000, and April 2001. Methoprene exposure had a negative impact on the reproductive potential of the crabs. Mean carapace width (CW) and wet weights increased from 13.82 � 1.10 mm and 1.04 � 0.26 g in May, respectively, to 17.41 � 1.19 mm and 2.32 � 0.30 g the following April. The peak mean ovarian index (OI) occurred in August, followed in September by a precipitous decline due to hatching of the young from the attached egg mass. Both exposure levels resulted in reduced percentages of total vitellogenic females (primary plus secondary VTG) in August 2000 – April 2001. Reduced OI were observed in the low-dose and high-dose crabs (-16.7% and -10.2%, respectively) relative to the reference group at its peak of ovarian maturation in August 2000. The April 2001 sample showed 23.8% and 75% reductions in OI, 10.6% and 25% reductions in total number of vitellogenic females, and 29.5% and 50% reductions in number of secondary VTG females in the low- and high-dose groups, respectively, as compared with the April 2001 reference group. Reduction in the number of reproducing females and OI (as related to fecundity) affected by exposure to methoprene could seriously diminish the reproductive potential of crab populations chronically exposed to environmentally relevant concentrations of this juvenile hormone analog.