The study considers 214 valid bee species that Robertson collected plus an additional 14 species found by us but not by Robertson. Of these 214, we collected 140 species. The absence of most of the remaining 74 species that we did not collect can be explained by examining their plant preferences. Robertson did not record 47 of these 74 species on the 24 plant species where we collected intensively, and he observed 19 more species on only one or two of the 24 plant species. Additionally, he observed 21 of them on only one of the 441 plants he studied. Of the bee species found by Robertson on the 24 plant species, we collected 82% on the same plant species.
The land uses and land cover on Macoupin County's 225,464 ha (558,080 acres), which bear directly on the type and availability of habitat for bees and their host plants, varied considerably over two centuries. For example, in the early 1800s, land cover was about 73% prairie and 27% forest. The estimated 59,792 ha (148,000 acres) of forested land in 1820 diminished to 24,644 ha (61,000 acres) by 1924. It then grew to 34,340 ha (85,000 acres) by 1962. Agriculture is the predominant land use; in 1967, 59% of the land was in harvested crops (primarily row crops) and 15% was in pasture. Despite habitat changes and the passage of 75 years, our 1970 and 1972 Carlinville collections show a high degree of similarity with those of Robertson, possibly because diverse habitats within the agricultural matrix contained the host plants and nesting sites required by the bees. We recommend that a third survey of this area be undertaken as part of a long-term study made possible by the meticulous 19th century records of Charles Robertson, which must be preserved.