d to private lands studied over 50 years ago.
Another large-scale survey was conducted by Siemann et al. (1996; Long Term Ecological Research, University of Minnesota) in 1992 in Cedar Creek, Minnesota. Sweep samples of 48 grassland fields were conducted 7-9 times during the growing season, with 100 sweeps per sampling date. 89,596 insect specimens of 1167 species were collected, and 90% of the specimens were identified to species. The data set was used for analysis of diversity, abundance, and body size relationships of insects, but it might lend itself to reanalysis for patterns in anthophilous fly distribution. LTER sites could be targeted as locations for these types of surveys, to be repeated on a long-term basis.
In 1984, D. Inouye and M. Soulé initiated several long-term monitoring projects related to organisms occurring in the area of the Rocky Mountain Biological Laboratory (RMBL) in Colorado (latitude N 38.5°, 106° W). Malaise trapping has been continued since that time (D. W. Inouye, unpublished data). Samples were collected weekly throughout the growing season from June through late August at Gothic Research Meadow (elevation 2912 m). In 1991, trapping began at two additional sites in the area (Cement Creek, elevation 2830 m; and Washington Gulch, 2978 m). The malaise trap catches were sorted to insect order, and the numbers of flies in certain families of interest were recorded for each sample. Relative weather data were recorded for each 72-h collecting period, and could be supplemented by more detailed weather data from the RMBL weather station. The peak number of Diptera within each years’collections ranges from a low of 280 in 1995 to over 1665 individuals in 1985. Preserved specimens are in storage for future extended analysis.Dipteran species composition
Differences in dipteran species composition between natural and disturbed areas can be dramatic, and can serve as excellent indicators of environmental degradation (Bañkowska 1980). In an extensive 5-yr survey of syrphid biogeography in Poland, Bañkowska (1980) compared the syrphid fauna of multiple natural areas with those from areas subjected to mild, moderate, and intensive anthropogenic pressures. She documented a lower species diversity in urban and agricultural areas. Both were dominated by syrphid species with broad distributional ranges, good colonizing abilities, and high ecological tolerances. In comparison, natural habitats were species-rich and characterized by shifting proportions of species, as one moved from one habitat toward another. There were characteristic species associations for each distinct habitat type. Syrphid fly species composition closely followed patterns of food supply and habitat condition.
The following example illustrates Bañkowska’s findings: In total, 73 species were collected in the city of Warsaw, compared to 128 species in natural areas containing Warsaw’s pre-urban habitat of oak-hornbeam forest. Only 66 species inhabited urban parks, and 46 species inhabited green areas around housing estates. The proportion of phytophagous and terrestrial saprophagous species dropped significantly, with only four species of phytophages present near the housing estates. These four were pests that eat ornamental plants, or weed-eating species. Urban areas were dominated by four syrphid species with broad geographic ranges
Clearly, this type of information on dipteran species composition will be invaluable in determining whether North American fly pollinators are in decline. Bañkowska’s comparison of species composition in disturbed and natural habitats is a good model for the type of study needed in North America. This type of study could be tied to a second project estimating the pollination value of different dipteran species.
In Japan, a broad-scale, four-year survey compared all insect visitors to roughly 100 plant species in each of three different habitats (Inoue et al. 1990, Kakutani et al. 1990, Kato et al. 1990). The habitats included a university campus with mostly exotic vegetation, an undisturbed oak forest, and a bot