The state of Utah is located in a semi-arid climatic zone and contains about 52.7 million acres of land which varies topographically from smooth desert plains and valleys to steep mountain ranges (8).

The production of livestock in Utah is important to the economy of the state. The economic life of many communities throughout the state depends on income from livestock. Cash receipts from range livestock were $62.7 million or 38.8 percent of the total from agriculture in Utah in 1958 (18). Much land in Utah is used almost exclusively for livestock production. Of the 52.7 million acres in Utah about 78 percent is used for the production of range livestock (15). Sheep obtain approximately 86 percent and cattle 56 percent of their forage needs from range lands (15, p.28). Although there are alternative uses for some areas, grazing livestock is the only significant economic use for much range land in the state.

Populations of Delphinium occidentale (Ranunculaceae)were monitored over two summers for the presence and dispersion of various life stages of several host specific phytophagous insects. Observations were made at several sites in the Wasatch National Forest east of Logan, Utah. Two species of larkspur aphid (Aphis rociadae and Kakimia wahinkae) were encountered. Although dispersal of alate individuals resulted in widespread infestation of the host plant population, aphids occurred initially on the same one or few plants at each site both springs. Little coexistence of the two species of aphid on the same plant was observed, perhaps because they partitioned the host plant resource according to light intensity under the incomplete aspen canopy. Several species of lepidopteran larvae, of uncertain host specificity, were observed. Two species (Autographa californica and pyrrhia expremins: Noctuidae) are known from cultivated host plants. Eggs of an unidentified geometrid (Lepidoptera) were located on the host plants in large numbers and their dispersion was analysed. The eggs were distributed nonrandomly over the host plant population, but attempts to further characterize the pattern were fruitless. Parasitism of the eggs by an unidentified hymenopteran was observed. Mortality of all larvae was high. Successful migration of larvae was not observed. Mature larvae were not sufficiently abundant to permit statistical study of pattern. Mature fruits were examined at the end of the growing season for larkspur maggots (Hylemya laxifrons). Maggots were found in 85 percent of the inflorescences sampled. Pteromalids (Hymenoptera) were also found in an apparently parasitic relationship with the maggots in the fruits. Maggots were not found in the surviving fruits of inflorescences infested with either species of aphid. Suggestions are given for future work.