GRIGGS, JL*; BELDEN, LK; Virginia Polytechnic Institute and State University: Decreased survival of trematode cercariae Echinostoma trivolvis following atrazine and metolachlor exposure

Atrazine and metolachlor are two widely used agricultural herbicides that inhibit the growth of pre-emergent vegetation. Residues of these pesticides are commonly found in bodies of water near agricultural areas. While extensive studies have been conducted on individual pesticides and their effects on single species, less is known about the effects that pesticides can have in more complex biological systems, such as host- parasite systems. We are examining pesticide impacts in aquatic disease systems involving digenean trematodes with complex life cycles (a definitive host and two intermediate hosts). In this study, we investigated the effects of environmentally realistic concentrations of atrazine and metolachlor on the survival of trematode ( Echinostoma trivolvis ) cercariae. Cercariae are a free-swimming trematode stage that emerges from the first intermediate host and infects the second intermediate host. Cercarial survivorship was monitored every two hours for 21 hours after exposure to low dose (3 ppb and 15 ppb) and high dose (100 ppb) concentrations of metolachlor and atrazine individually and as mixtures (10 ppb: 15 ppb, 85 ppb: 100, respectively). Control cercariae survived significantly longer than any of the pesticide exposed cercariae. Within the pesticide exposed groups, cercariae exposed to metolachlor survived significantly longer than those exposed to any dose of atrazine or to the pesticide mixtures. The results suggest that E. trivolvis cercariae are sensitive to both pesticides, although perhaps more so to atrazine. These changes in parasite survivorship can potentially affect trematode disease dynamics in polluted systems by altering parasite loads in hosts, rates of disease transmission, and natural population regulation and stability.