. The Canadian field-naturalist. The Canadian Field-Naturalist Vol. 114 live south of Ontario in the Atlantic Coastal Plain. Whether T. pechumani moved northward with these insects or delayed entry until optimal habitat require- ments were established is unknown. By 7500- 7000 yr B. P. insect assemblages in the region were similar to those found in southern Ontario today, , the modem fauna was established (Morgan 1987). Tachysphex pechumani probably entered south- western Ontario before the expansion of the decidu- ous forest which occurred between 7000 and 6000 yr B. P. (Table 1). Closed
. The Canadian field-naturalist. The Canadian Field-Naturalist Vol. 114 live south of Ontario in the Atlantic Coastal Plain. Whether T. pechumani moved northward with these insects or delayed entry until optimal habitat require- ments were established is unknown. By 7500- 7000 yr B. P. insect assemblages in the region were similar to those found in southern Ontario today, , the modem fauna was established (Morgan 1987). Tachysphex pechumani probably entered south- western Ontario before the expansion of the decidu- ous forest which occurred between 7000 and 6000 yr B. P. (Table 1). Closed forest was detrimental to this species because it supplanted the sandy openings and savanna necessary for mating, hunting and nesting (Kurczewski 1998). Prior to that time, invasion by thermophilous deciduous species was suppressed by the cooler climatic conditions associated with the Laurentide Ice Sheet. This ice sheet did not disinte- grate to a size where its effects on the environment were negligible until after 8000-7500 years ago. Then, summer warmth was established in the lower Great Lakes Region facilitating the northward move- ment of the thermophilous species (Anderson and Lewis 1992). Aided by an ameliorated climate, Beech (Fagus grandifolia). Hemlock (Tsuga canadensis). Sugar Maple (Acer saccharum), elm (Ulmus spp.), oak {Quercus spp.), Basswood {Tilia americana), and White Ash {Fraxinus americanus) largely replaced White Pine (Pinus strobus) on the mesic soils of the region (Anderson 1995; Bemabo and T. Webb 1977; Karrow and Warner 1990; McAndrews 1981; Mott and Farley-Gill 1978; Schwert et al. 1985). White Pine remained abundant on the droughty soils of the Norfolk Sand Plain and other extensively sandy and gravelly areas in south- western Ontario until the expansion of oak [probably White Oak {Quercus alba) and Black Oak {Q. veluti- na)] about 6500-6000 yr B. P. (Bennett 1987; Szeicz and MacDonald 1991) (Table 1). Favorable conditions for the entry of T. pechu-
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