HATCHING AND DEVELOPMENT OF RANGELAND GRASSHOPPERS (ORTHOPTERA, ACRIDIDAE) IN RELATION TO FORAGE GROWTH, TEMPERATURE, AND PRECIPITATION

Sampling of a grasshopper (Acndidae) population weekly during the summer months of 1975, 1976, and 1977 showed that hatching began when the soil temperature (one cm below the surface) was above 15.6°C for a total of at least 200 h and when the degree hours (number of degrees each hour that the soil temperature exceeded 15.6°C) totaled 2466. Grasshopper density decreased from 1975-77. In 1975 Melanoplus sanguinipes (F.) totaled 53% of the number collected; in 1976 and 1977', Amphitornus coloradus (Thomas) was most abundant and comprised 23% and 30%, respectively, of the population. Grasshoppers became active at surface temperatures (5 cm above ground) of 13°-16°C, and feeding began at 21°C. Threeyr averages showed the surface temperatures remained above 21°C for 12 h each day in July, 10 h in August, and 8 h in Sept. Seasonal growth, including seed set, of 3 grass species (western wheatgrass-needleandthread-prairie junegrass) was mostly completed before grasshoppers developed to the damaging stage (4th and 5th instars and adults). Clipping studies snowed that grass and forb production decreased from 1473 kg/ha in 1975 to 503 kg/ha in 1977 and was directly correlated with spring and summer precipitation. Forage lost to grasshoppers was estimated at 235 kg/ha in 1975, 226 kg/ha in 1976, and none in 1977. © 1979 Entomological Society of America.