Great Basin Naturalist


Migrating bands of Mormon crickets (Ananbrus simplex) were observed crossing the Green and Yampa rivers in Dinosaur National Monument, Colorado and Utah, in 1986 and 1987. Swimming crickets were swept downstream and eaten by four endemic and seven introduced fish species. Included were two endangered fishes, Colorado squawfish (Ptychocheilus lucius) and humpback chub (Gila cypha). Direct and indirect effects to aquatic food webs associated with application of pesticides for Mormon cricket control may pose a threat to these fishes and to man.