EFFECTS OF THE PESTICIDE METHOPRENE ON MORPHOGENESIS AND SHELL FORMATION IN THE BLUE CRAB CALLINECTES SAPIDUS

The juvenile hormone analog methoprene causes both cytologic and biochemical alterations in larval and adult stages of the blue crab Callinectes sapidus. This insect growth regulator, used for mosquito control, caused (at a concentration of 10 gM) profound ultrastructural changes in the cuticular epithelial cells of postmolt adult blue crabs studied in vitro; these changes included loss of secretory organelles as well as distention and blebbing of the outer membrane of the nuclear envelope. Biochemically, 10 gM methoprene caused decreased deposition of extracellular cuticular chitin and protein, as well as a remarkable intracellular accumulation of chitoprotein precursors. These findings suggest that methoprene alters exocytosis and deposition of cuticular components. In vivo studies indicated that 5-10 gM methoprene is able to penetrate the embryonic investment coat to localize in lipovitellin. Exposure to methoprene at environmental concentrations (2-10 giM) produced morbidity and mortality in the form of an overall reduction in the number of successful hatching and lethargic behavior exhibited by the surviving zoeae. Methoprene exposure (3.3 gM) was also toxic to megalopae, delaying the molt to the first crab form and resulting in death of 80% of larvae after 10 days. The blue crab Callinectes sapidus Rathbun is a crustacean of both ecologic and economic importance to the coastal zones of the eastern and southern United States. Its life cycle and feeding habits bring it into estuarine environments subjected to pesticide treatments for mosquito control. It is logical to assume that the blue crab might be impacted by compounds active in other arthropods. The pesticide methoprene, a compound frequently applied to wetlands and salt marshes, belongs to the group of pesticides known as insect growth regulators (IGRs), which, in general, exert their toxic effects by disrupting insect development and/or reproduction. We offer in this report evidence that methoprene can penetrate the embryonic cuticle and can produce morbidity and mortality in larval forms of the blue crab. We also present in vitro findings indicating that methoprene may be toxic to the adult blue crab as well by altering the exocytosis of cuticular material.