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Table 3..--Mean spruce budworm performance (female equivalents) on white spruce in 1991 on early, middle, and late
phenology trees and flowering and nonflowering trees. Means varying significantly (p < 0.05) due to main effects
have different letters. Only mean weight and development time were affected by phenology. There were no flowering
effects.
Budworm performance Tree phenol0_y class Tree flowering, class
variable Early Middle Late Yes No
Cohort one
Survival (larvae) 0.57 0.57 0.55 0.57 0.57
Weight dwt (rag) 28.61b 30.96a 32.48a 30.13 311.33
Dev. time (days) 41.11 40.93 40.85 40.96 40.95
Growth rate (mg/da) 0.70b 0.76a 0.80a 0.74 0.77
F x P had any significant (p < 0.05) effects on growth, development time, or growth rates. Although, there was a hint (p <
0.08) of a tendency for nonflowering trees to be superior for larval performance than flowering trees (Fig. 2).
DISCUSSION and CONCLUSIONS
Yearly Differences in Protocol and Weather Weaken the Tests
The differences in the effects of flowering and phenology on spruce budworm performance between years is ahnost
certainly due to the differences in host tree phenology when the studies were initiated. In 1989, we placed our first cohort of
budworms on the trees at 133 degree days (dd), very close to the time native budworm populations would have been emerging
(est. at 100 dd). The second cohort was placed out at 204 dd, 71 dd and 7 days later than the first. In 1991 the experiment
was begun 10 calendar days earlier than in 1989 but at a phenologically later point, 210 dd, about the time of budbreak
on the early flushing trees (Nienstaedt and King 1970). Hence, the first cohort in 1991 was more nearly equivalent to the
second cohort in 1989. The second cohort on fir in 1991 was placed on the host plants at 262 dd thereby having no 1989
equivalents. Finally, the single cohort on spruce in 1991 was placed on the trees at 280 degree days, about the time of
budbreak for the later flushing spruce trees (Nienstaedt and King 1970). In addition, in 1991, just after placing the first
cohort of second instars on the trees, the weather turned cool and wet keeping the young insects in their overwintering
hibernaculum until nearly 1 week later when the next cohort was being placed on the trees.
Although this study attempted to examine the combined effects of staminate flowering by host phenology on the
performance of spruce budworm, we were unable to execute the experiment in perfect phenological duplication that would
have allowed the most powerful tests of the hypotheses.
Flower by Phenology Effects
, The data clearly suggest that the survival of budworms is dependent on the flowering x phenology interaction of its
host plants. In the case of fir, abundant flowering probably enhances survival most significantly on the later flushing trees,
i.e., late relative to budworm emergence (they inevitably emerge before their hosts break bud). This was apparent especially
in 1989. In that year all flowering branches supported higher survival than nonflowering branches regardless of tree phenology
class, and regardless of cohort timing. In 1991 there was no apparent flowering effect on survival except for the late
flushing trees, especially in the case of the second cohort. Likewise, on spruce there was a strong tendency, though only
nearly significant (p