Monophagy in a polyphagous grasshopper,Schistocerca shoshone

The feeding behavior of different populations of the grasshopper,Schistocerca shoshone, was investigated in the southwestern United States. Insects from three riparian populations, with a broad spectrum of plants available to them, tended to eat plants roughly in relation to their availability except that broad-leaved herbaceous plants were avoided. Insects from a desert population in a plantation ofSimmondsia fed exclusively on that plant, as did those from another population in the Tucson mountains, despite the availability of a range of other plants. Insects from a third desert population, near Portal, fed mainly onProsopis, the dominant woody plant. In detailed behavioral experiments in the laboratory, insects from Tucson mountains readily acceptedSimmondsia, and less readily acceptedProsopis. Three other common woody plants from the habitat were generally rejected without feeding. Insects from Portal acceptedProsopis andSimmondsia with approximately equal readiness. Breeding experiments suggested that the differences between the plantation insects and those from Portal was genetic and not induced by experience. The insects from both populations were potentially polyphagous and ate a wide range of plants in the laboratory if given no alternative.