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.-- Jr ~ (Ylt ncJI ~I 1 q '8~ 073)2 MIGRATING MORMON CRICKETS, ANABRUS SIMPLEX (ORTHOPTERA: TETIIGONIIDAE), AS FOOD FOR STREAM FISHES , 'I ,I Harold M. Tyusl and W. L. Mincklei ABSTRACT.-Migrating bands of Mormon crickets (Anabrus 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. J ~ The Mormon cricket (Anabrus simplex Haldeman) occurs only in western North America where it is generally regarded as an agricultural pest (Wakeland 1959). This flightless, long-horned grasshopper is primar- ily solitary in low-density subpopulations but becomes gregarious and migratory with high densities, moving from its mountain breeding areas to plague croplands (Capinera and MacVean 1987), Earliest records of this insect date to Mormon pioneers in the Salt Lake Valley in 1847 and to the legendary cricket plague ofl848 (Bancroft 1889, Whitney 1892), Although most reports stress the detrimen- tal effects of Mormon cricket outbreaks, Mor- mon crickets potentially provide an abundant and high-quality food source (Defoliart et at 1982), Predation by terrestrial animals in- cludes about 50 species of birds, mammals, and reptiles; however, references to preda- tion by aquatic animals are few (Wakeland 1959), Mormon crickets swim readily (LaRiv- ers 1956), as do other Orthoptera, and refer- ence to their movements into Utah streams and lakes dates to 1848 (Bancroft 1889). Swim- ming crickets would be exposed to aquatic predators during migrations, but we found no reference to predation on this species by fishes. Annual Mormon cricket outbreaks and mi- grations in Dinosaur National Monument (DNM), Colorado and Utah (Fig, 1), have re- newed an old controversy about control of crickets by aerial spraying of pesticides (Cap- inera and MacVean 1987), U,S, Fish and Wildlife Service 1986, 1987), A part of this IU.S. Fish and Wildlife Service. 1680 West Hwy 40, Room 1210. Vernal, Utah 84078. 2Department of Zoology, Arizona State University, Tempe, Arizona 85287 controversy concerns Park Service policy to treat crickets with natural controls, if needed (National Park Service 1986), since aerial spraying could adversely affect endangered species in DNM. The objectives of this study are to evaluate fish predation on Mormon crickets in DNM, discuss possible signifi- cance to fishes of a periodic, massive, and seasonal food supply, and comment on possi- ble impacts of cricket controls on fishes, aquatic communities, and man, METHODS The availability of Mormon crickets in streams and predation on them by fishes were evaluated by visual observations, use of crick- ets as bait, and direct inspection of stomachs of nonnative species taken by angling, tram- mel nets, and electrofishing. Angling in- cluded bottom-fishing with weighted hooks and surface-fishing with floats, Mormon crick- ets were hooked through the thorax and abdo- men, Weekly trips through the Green and Yampa rivers in 1986 and 1987 (May through July) included the season when crickets were present, Average weights of late instar and adult Mormon crickets were obtained in 1987 by weighing 20-50 individuals from several large bands, All crickets in a 5-30-m section of road were collected and weighed on a 1,000 X 2-g platform scale. Crickets were placed in previ- ously tared plastic bags,. and subsamples were separated by sex. Cricket bands were located on Harpers Corner Road in DNM from 19 July to 14 August 1987, 25