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Table l.--Comparing the mean numbers of insects and adelgid galls on blue, hybrid, and white spruces, using visual
examination of two random midcrown branches per sample tree at the Kellogg Experimental Forest during late
May-early June, and mid-late July. N = 30 - 42 trees.
Insect Species Time period l: nos.! 2 branches Time period 2: nos./2 branches
B.Spruce Hybrids W.Spruce B.Spruce Hybrids W.Spruce
A. abietis galls 0.07b _ 1.14a 2.25a 0.00b 2.20a 2.27a
A. cooleyi galls 0.03b 0.36a 0.00b 0.00b 0.33a 0.07b
A. cooleyi alates 0.17b 24.76a 0.00b 0.00b 4.66a 0.00b
Pineus similis galls O.OOa O.OOa O.19a O.OOa O.OOa O.OOa
Means with different letters within time periods are significantly (p < 0.05) different.
Species Loading, and Total Insect Loading Comparable Among Hybrids and White Spruce
At Kellogg, the hybrid and white spruce herbivore species loadings were statistically equivalent (ca. 3 - 3.3 per
branch) and significantly higher than those of blue (I.9) in the first sample, but not in the second, when all three spruces were
statistically equivalent. At Dunbar, the hybrids, and white spruce also had equivalent herbivore loadings (ca. 3 - 3.8 species
per branch) which were significantly higher than those (ca. 1.2 - 1.5 per branch) of blue spruce in both first and second
samples (Table 2).
Table 2.--Comparing mean numbers of phytophagous insect species, and total insect numbers occurring in beating samples
from blue, hybrid, and white spruces at two study sites in Michigan.
Study area and Mean nos. insect species per branch Mean nos. of insects per branch
sample period
B.Spruce Hybrids W.Spruce B.Spruce Hybrids W.Spruce
Dunbar- 1 1.50b _ 2.96a 3.79a 2.42b 4.17a 6.71 a
Dunbar-2 l. 17b 3.21 a 3.00a 1.25b 4.33a 4.71 a
Kellogg-1 1.87b 3.31a 2.97a 1.13b 4.27a 4.23a
Kellogg-2 2.97a 2.17a 2.90a 2.20a 2.12a 1.97a
Means having different letters within an area and sample period category are significantly (p < 0.05) different.
At Kellogg, there were 20 species of phytophagous insects on the hybrids, of which they shared 12 in common (60%)
with white spruce (Fig. l). At Dunbar, we found twice as many (41 ) species of phytophagous insects on the hybrids, of
which 33 (80.5%) they shared in common with white spruce (Fig. I). About 12-15% of the hybrid's phytophagous insects
were "unique" at both sites, because they did not share these species with either white or blue spruce. About 49-60% of their
total species pool, they shared with blue spruce. These data confirm the expectation that the phytophagous insects occurring
on the hybrids are largely those commonly associated with white spruce. The same is true for blue spruce, which had a total
of 23 species at Kellogg and 24 at Dunbar, of which 19 were shared in common with white spruce at both sites.
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