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Table 2.---Mean spruce budworm performance (female equivalents) on balsam fir in 1991 on early, middle and late phenology
trees (main plots) and flowering and nonflowering branches (subplots). Means varying significantly (p < 0.05)
among main effects have different letters. For cohort one, mean weight and growth rate were significantly affected
by phenology, and mean development time by the f x p interaction. For cohort 2, only mean survival was significantly
affected by flowering, and by the flowering x phenology interaction.
Budworm performance ..... Trees, (main plots)--Phenology class SubplotmFlowerin_g "class
variable Early Middle Late Yes No
Cohort one
Survival (larvae) 0.41 0.41 0.44 0.42 0.42
Weight dwt (rag) 23.41b 26.47a 25.72a 24.79 25.00
Dev. time (days) 51.29 50.97 51.05 51.05 51.23
Growth rate (mg/da) 0.46b 0.52a 0.50a 0.49 0.49
Cohort two
Survival (larvae) 0.45 0.47 0.43 0.47a 0.4 l b
Weight dwt (rag) 24.37 25.27 25.53 24.51 25.44
Dev. time (days) 46.02 46.16 45.65 45.92 45.95
Growth rate (mg/da) 0.51 0.55 0.56 0.53 0.55
Larval Growth
There were no significant flower or F x P effects on weight gain (mg dwt) by the first or second budworm cohort in
either 1989 or 1991 (Tables 1,2). However, there was a significant phenology effect on cohort 1 in 1991, where middle and
late flushing trees yielded bigger adults than early flushers (26.5 vs 23.4 mg dwt).
Likewise, there were no significant flowering, or F x P effects on budworm growth rates (mg/da) for either cohorts in
1989, and 1991 (Table 1, 2). However, there was a significant phenology effect on the growth rate of the first 1991 cohort.
Budworms on middle and late trees grew faster than those on early flushing trees (0.52 mg/da vs 0.46 mg/da). There was
also a significant F x P effect on development time for cohort one (Fig. 2), but this may have been spurious.
Comparing the grand means for cohorts 1 and 2 in 1989revealed that growth (22.95 vs 24.31 mg) was significantly
higher and development shorter (53.13 vs 50.97 da) for the second than first cohort. By contrast, in 1991, there were no
significant differences in overall growth between the two cohorts, but development time was, as before, much shorter for the
second (51.14 vs 45.93 da), causing its growth rates to be significantly higher (0.49 vs 0.54 mg/da).
Survival
White Spruce: Flowering and Phenology Effects on Budworm
Flowering and phenology had no significant effects on survival of larvae (Table 3), but the F x P interaction was
nearly, significant (p < 0.10). There was an apparent trend for survival to increase with increasingly retarded phenology on
nonflowering trees, and the opposite trend on flowering trees (Fig. 2). The fact that the two trends run counter to each
explains why the main effects of flowering and phenology were insignificant. The grand means from flowering and nonflowering
trees in each phenology class canceled one another out.
Larval Growth
There were strong, consistent phenology effects on both total weight gain and growth rates, the pattern being identical
on both flowering and nonflowering trees (Table 3). Budworm mass and average growth per day increased with increasingly
retarded tree phenology, Insects on the late flushing trees averaged 13.5% larger than those from the early flushing trees
(32.5 mg vs 28.6 rag). Likewise their daily growth rates were 14.5% higher (80 mg/da vs 70 mg/da). Neither flowering, nor
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