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41 40
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42 41
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42 40 40
41 / 42
40 43
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45
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48 I 1
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49 49 50
Figure 1.--Average annual mean temperature isotherms for Michigan in °E based on the period 1940-1969 (MDA 1974).
Inset shows Michigan, with county-level resolution, the surrounding Great Lakes (shaded area), and outlines of
several adjacent states and Canada. Approximate °C equivalent values are: 40°F = 4.4°C, 41 °F = 5.0°C, 42°F = 5.60C,
43°F = 6.1 °C, 44°F = 6.7°C, 45*F = 7.2°C, 46°F = 7.7°C, and 47°F = 8.3°C
Models of global warming in the northern hemisphere predict that a species range will change most dramatically
along the southern limits of its range (Cannell et al. 1989, Botkin and Nisbet 1992, Woodward 1992, Matyas 1994, Sykes and
Prentice 1995). Fortunately, in southern Michigan there is a paper birch progeny test (Fig. 2) that consists of over 200 halfsib
(i.e., where the identity of the maternal parent is known) families that were collected from throughout the natural range of
birch in Michigan. In addition, it is coincidental that the mean annual temperature varies by about 10°F (5.6°C) between the
southern and northern extremes of Michigan (Fig. 1). Therefore the paper birch trees growing in the genetic test plantation in
southern Michigan are theoretically experiencing an increase in mean annual temperature of 1° to 5°C. Given that the bronze
birch borer preferentially attacks weakened birch trees, it seems plausible that borer attack could vary among seedlots of
varying geographic origins if they were experiencing differential levels of stress.
The bronze birch borer, like many other buprestids in the genus Agrilus, usually attacks host trees that are stressed by
drought or repeated insect defoliation (Anderson 1944; Clark and Barter 1958; Barter 1965; Carlson and Knight 1969; Haack
and Benjamin 1982; Haack and Slansky 1987; Mattson and Haack 1987a, 1987b; Haack and Mattson 1989; Herms 1991;
Herms and Mattson 1991; Wargo and Haack 1991; Haack 1992; Haack and Acciavatti 1992; Solomon 1995). The biology
and life history of the bronze birch borer has been reported by several authors (Chittenden 1898; Balch and Prebble 1940;
Anderson 1944; Barter 1957; Ball and Simmons 1980; Loerch and Cameron 1983, 1984; Akers and Nielsen 1990; Wilson
and Haack 1990). Briefly, the bronze birch borer is univoltine. Adult beetles emerge in early summer from within their host 235
50
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