Virulence of Metarhizium anisopliae to Embryos of the Grass Shrimp Palaemonetes pugio

Experiments were performed in which developing embryos of the grass shrimp, Palaemonetes pugio, were exposed to conidiospores of the insect pathogenic fungus, Metarhizium anisopliae. Responses were variable, with significant (P </= 0.05) adverse effects observed in five of six experiments conducted. Dead embryos and larvae with visible growth of M. anisopliae were observed in all experiments. Growth of M. anisopliae was occasionally observed on embryos and larvae prior to death. Delayed hatch was also observed. In one of the initial experiments, an increase in N-acetyl-beta-d-glucosaminidase, EC 3.2.1.30 (NAGase), activity accompanied by an increase in virulence toward shrimp embryos was observed. Additional experiments in which conidiospores were produced on homogenized caterpillars suggested a positive correlation between virulence of M. anisopliae to P. pugio embryos and activity of spore-associated NAGase. Under these laboratory conditions M. anisopliae was an invasive pathogen of grass shrimp embryos, and the growth substrates on which their spores develop can influence the severity of effects on these nontarget arthropods.