Effects of Malathion on Petrolisthes armatus

The green porcelain crab, also known as Petrolisthes armatus, is an invasive species to the South Atlantic coast and highly sensitive to malathion. Malathion is a commonly used pesticide used on crops and lawns; it can be found in runoff leading into estuaries, rivers, and other sources of water. Two LC50 tests were carried out to determine the concentration of malathion for P. armatus that would kill 50 percent of the test subjects. P. armatus was tested in malathion at the following concentrations: 0.1 µg/L, 1 µg/L, 10 µg/L, 100 µg/L, 500 µg/L, 1,000 µg/L, 10,000 µg/L, and 100,000 µg/L. The LC50 value was 10 µg/L indicating that malathion was extremely lethal to P. armatus. Malathion, an organophosphate, caused spontaneous autotomy and catalyzed the molting process for many of the crabs. In most treatments only one of the chelipeds was lost; in most cases it was the left cheliped. The results of this study show that malathion is harmful to this invasive species. Malathion is a common household pesticide and runoff from homes near marsh banks can end up in nearby oyster beds despite the half life of malathion. P. armatus is an indicator of such toxins because they are highly sensitive to malathion.