Acute Effects Of Methoprene On Survival, Cuticular Morphogenesis And Shell Biosynthesis In The American Lobster, Homarus americanus.     Michael N. Horst1, Anna N. Walker2, Robert Vogel3, Thomas G. Wilson4, Parshall B. Bush5, Ernest Chang6, Timothy Miller7   Departments of  1Basic Medical Sciences, 2Pathology and 3Family Medicine, Mercer University School of Medicine, Macon GA; 4Department of Biology, Colorado State University, Fort Collins, CO; 5University of Georgia, Athens, GA; 6Bodega Marine Laboratory, UC Davis, Bodega Bay, CA; and 7Darling Marine Center, University of Maine, Walpole, ME     The1999 lobster mortality in WLIS coincided with the application of pesticides including methoprene.   Lethal effects were also observed on several species of crabs. In addition to pesticides, stress in crustaceans may be due to altered temperature and salinity of WLIS after Hurricane Floyd. Reports of gravid female lobsters that died while attempting to molt suggest endocrine disruption had occurred, since molting is normally inhibited in gravid females. Three factors may have contributed to the WLIS mortality: acute dose of methoprene, lower than normal salinity and above normal water temperatures. Our objectives were: (1) to determine both lethal and sublethal doses for methoprene in all life stages of the American lobster at various salinities and temperatures; (2) to investigate the cytopathology of methoprene treated tissues; (3) to conduct biochemical studies on the effects of methoprene on shell formation in lobsters; (4) to evaluate stress protein induction in lobsters by methoprene; and (5) to examine bioaccumulation and metabolism of methoprene in lobster tissues. Methoprene is toxic to crustaceans  from 1.5-125 ppb and causes cellular abnormalities and decreased shell synthesis in blue crabs. It penetrates the egg case of blue crabs and disrupts embryonic development before emergence of the first larval stage. If methoprene acts similarly in lobsters, then significant decreases in numbers of new lobsters could be observed in future years. Preliminary results indicated that methoprene localizes in certain tissues within postmolt and intermolt lobsters, specifically epithelial cells underlying the shell, the digestive gland or hepatopancreas and nerve tissue; little methoprene accumulates in muscle. Methoprene treatment of adult lobsters causes increased formation of certain proteins in the hepatopancreas and decreased levels of others. NOAA/Sea Grant as part of the NY/CT Lobster Mortality Initiative sponsored support.