nt species were observed in proportion to their abundance in the habitat. Flies made roughly 10% of the visits to flowers at the woodland site, and over 90% of the visits at the tundra site.
Catherine Reed (1995a, b) monitored species richness of insects on prairie flowers in southeastern Minnesota for three years. She worked in eight separate prairie remnants or prairie reconstruction sites, hand-collecting all insects during 15-min sampling sessions on each plant species that had at least 100 open flowers (59 plant species). The focus of the study was to compare diversity in reconstructed sites with diversity in remnant prairie patches. Collections were made from late May through late September on sunny days when temperatures were between 20° and 35°C. Insects were identified to species. Sixty fly species were collected, some in reconstructions, others in remnants, some in both. Reed revisited the sites in the summer of 1999, and says the study is “quite repeatable,” although some of the sites have changed. Native prairie sites are now managed more intensely with brush-cutting, burning, and planting of seeds (C. Reed, personal communication).
Kearns (1990) and Kearns and Inouye (1994) monitored visitation rates to Linum lewisii (Linaceae) for three summers at three different elevations in the area of Rocky Mountain Biological Laboratory, Gothic, Colorado (38.5°N, 106.5° W; 2780 m, 2886 m, and 3475 m). Visitation data were recorded for bees and fly families. Fly visitation rates differed significantly among sites, but did not differ significantly among years. However, additional visitation data collected at the 2886m site in the two proceeding years showed that annual variation in visitation within a site can be large, in this case, as a result of an Entomophora outbreak in 1986 that reduced fly numbers. Visitation rates to Linum are highly correlated with Malaise trap fly samples from the same site (Kearns and Inouye 1994).
An attempt to document the conservation status of fly pollinators in North America reveals the need for further basic research into fly pollination systems, and into the natural fluctuations in dipteran abundance. The main impediment to implementing any of the large-scale studies recommended is that intensive collecting efforts produce large numbers of species that require identification. Fly species identifications are often difficult, and the number of fly taxonomists is limited. Revisions in taxonomy of certain groups may mean re-evaluating original sample material from historical collections. These problems are not unique to Diptera, but are common to any large-scale insect collections.
The abundance and diversity of anthophilous flies, their role in pollination systems, and their multiplicity of larval roles indicate that dipteran declines would probably affect multiple levels within communities. The development of checklists for specific areas (e.g., Biosphere Reserves or National Parks) would be a useful first effort (Disney 1986). Resampling in areas of well-documented studies would provide much needed data that would allow us to evaluate the conservation status of the group. Habitat conservation will ultimately be the most effective tool in conserving pollinating Diptera.
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