Carbon isotope ratios and crop analyses of Arphia (Orthoptera: Acrididae) species in southeastern Wyoming Grassland.

Food habits of Arphia conspersa Scudder and Arphia pseudonietana (Thomas) were studied along an altitudinal transect in southeastern Wyoming shortgrass mixed prairie. Stable carbon isotope ratios indicated that diets were significantly different between study sites, between species, and between sexes. These differences were found to be primarily related to the availability of different food plants along the transect, although species with the C3 pathway of photosynthesis were consumed in greater proportion than their availability in the habitat. The preference for C3 species is presumably related to their higher nutritional value and digestibility, in spite of the fact that more time and energy must be spent to locate these food plants in some of the habitats studied. This study demonstrates the utility of the carbon isotope method in studying plant-animal interactions in habitats containing both C3 and C4 plants.