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() Acute Effects of Methoprene on the American lobster, Homarus americanus.

Horst, M1, Walker, A1, Wilson, T2, Bush, P3, Chang, E4, Miller, T5, 1 School of Medicine, Mercer University, Macon, GA, USA2 Department of Entomology , Ohio State University, Columbus, OH, USA3 Agricultural and Environmental Service Lab, Univ. of Georgia, Athens, GA, USA4 Bodega Marine Lab, University of California at Davis, Bodega Bay, CA, USA5 Darling Marine Center, University of Maine, Walpole, ME, USA

ABSTRACT- As a result of the massive die-off of lobsters in the Western Long Island Sound in the fall of 1999, we have examined the acute effects of methoprene, an IGR pesticide included in a cocktail of pesticides directed against mosquitoes during a West Nile virus outbreak earlier that year. We have studied toxicity, bioaccumulation and biochemical effects of methoprene on all life stages of H. americanus. Larval forms of the lobster are more sensitive than postlarval forms while adults appear to be the least sensitive. The apparent 72 h LC50 for stage 2 larvae is 2.8 ppb; no anatomic cause of death is evident by routine light microscopy. While postlarvae survive exposure to 25 ppb methoprene, we observe increased rates of molting and death during molting at concentrations as low as 5 ppb. Treatment of explant cultures prepared from postmolt juvenile lobsters with methoprene causes alteration in a specific group of shell proteins, identified on Western blots by Tomato lectin binding. SDS-PAGE analysis of epithelial proteins showed that methoprene treatment causes alterations in the phosphorylation state of specific cellular proteins. In vivo and in vitro metabolic studies with 35S Translabel indicate that 50 ppb methoprene blocks hepatopancreatic protein synthesis by 90%, and also causes alterations in expression of specific stress proteins (Hsp 70, 72/3, Erk 1-2, heme oxygenase). Exposure of adult intermolt lobsters to 50 ppb methoprene leads to bioaccumulations of up to 250-fold in specific tissues: integumentary epithelium, hepatopancreas and gonads as measured by GC/MS. Most significantly, we observed 1,200-fold accumulation of methoprene in eyestalks. Exposure of day 1, stage 1 larvae to increasing concentrations of methoprene for 4 hours was followed by homogenization and analysis of relevant enzyme activities. Analyses of chitin synthase and esterase activities, as well as HSP alterations, are ongoing. This work was supported by a grant from the NY-CT WLIS Lobster Initiative Sea Grant Program.

Key words: crustacean, bioaccumulation, IGR pesticides, cuticle biosynthesis

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