ANTHOPHILOUS FLY DISTRIBUTION ACROSS AN ELEVATION GRADIENT

Flower-visiting Diptera are abundant in montane and Arctic areas. This research, conducted on the western slope of the Colorado Rocky Mountains: (1) characterizes the predominant anthophilous fly taxa in comparison with other high-elevation and high-latitude sites; (2) examines changes in fly abundance with elevation, and (3) examines the potential of flies as pollinators by examining quality and quantity of pollen loads. Flies collected from 66 flowering species were identified to species to produce a data base containing taxonomic information, elevation and floral records. Malaise trap censuses were conducted in three elevational zones. Pollen carried by flies and pollen in their guts were quantified and examined to determine the number of plant species represented. Proportional representation of dipteran families changed in a similar manner in different mountain systems and the Arctic. The predominance of flies on flowers at high elevations appears to be due to a decrease in representation of other orders of insects. Most fly taxa fed at multiple plant species, but gut contents indicated that individual flies fed largely on a single pollen type. Total pollen loads of flies and solitary bees were similar although flies collected on Linum lewisii carried less pollen than bees.