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later, we selected one more flowering and nonflowering branch on each tree which we once again enclosed with sleeve cages
arid ir_;e_ted about 20 second-stage budworms. These two batches came from the same population, and they were randomly
allocated to treatments. Hereafter, we respectively refer to them as cohort 1 and cohort 2. Approximately 2 weeks later we
removed the gauze patches and counted the number of larvae which failed to emerge from their overwintering hibernacula.
This gave us the initial number of insects in each sleeve cage. When most insects had reached the pupal stage, cages were
removed by cutting each branch at its base. We then searched each bag for budworm larvae and pupae. Pupae were stored
immediate[y in plastic vials and checked daily until all adults emerged. Moths were first frozen, then oven dried to constant
weight and weighed and sexed. Because male and females responded in the same way to treatments, we pooled sexes by first
converting males to female equivalents. Each male observation was multiplied by a constant (k) that was derived from the
grand meaas (gdm) of the particular variable in question (e.g., weight, developmental time, developmental rate, etc): k_= gdm
fcmate/gdm male, for each cohort and year. We calculated survival per sleeve cage by summing all larvae that achieved the
final 6th larval stage (even though some were parasitized or preyed upon by stink bugs), pupae, and adults, and divided this
grand total by the mm_berof larvae that actually emerged from their hibernacula.
In 1991, we selected 32 (16 flowering, 16 nonflowering) white spruce trees, Picea glauca, that were growing at the
edge of a provenance plantation (USDA North Central Forest Experiment Station) near Wellston, Michigan. Trees were
planted in 1963, and were approximately 8-10 m tall at the time of the experiment. Just as above we selected (on May 3) two
branci_es at midcrown level from each the flowering and the nonflowering trees for enclosure with sleeve cages and budworms.
We placed only one cohort of budworm larvae on these trees, however. We collected and counted surviving budworms
when most had reached the pupal stage.
Aft trees were scored for their phenological development according to the protocol of Nienstaedt and King (l 970) at
the time of placing insects on the trees.
Difference between cohorts 1 and 2 in the balsam fir study were first tested via a 2 x 2 factorial, randomized block
design where trees were treated as blocks and flowers and cohort timing were treated as treatments. Next each cohort was
analyzed separately to test specifically for flower by tree phenology effects on budworm performance (weight gain, growth
rate/day, days to complete development, and survival to the pupal stage). We subjected the data to univariate anova after
appropriate transflmnations of the data (i.e., arcsin (%survival)). The balsam fir study was analyzed as a completely randomized,
spiit,..piot design with phenology (3 classes) treated as the main plot and flowering (2 levels) as the subplot. The white
spruce study was analyzed as a completely randomized 3 x 2 (phenology x flowering) factorial.
Larval Survival
RESULTS
Balsam Fir: Flowering and Phenology Effects on Budworm
First cohort survival was clearly affected by both flowering (F) and flowering x tree phenology (P) classes (Table 1).
[n 1989, the significant F x P interaction was due largely to the enhancing effect of flowering, as expected, on the Sateflushing
trees, where survival averaged 65.3% with, and 43.2% without flowers (Fig. 1). The smallest flowering effect
occurred on early flushing tree (57.0% vs 53.6%, with and without flowers, respectively). In 1991, even though there were
no significant main or interactio_ effects (Table 2),the largest positive impact of flowering was evident on the late flushing
trees (as in 1989) where survival averaged 48.2% with, and 40.6% without flowers (Fig. 1).
Second cohort survival in 1989 was significantly (p < 0.02) enhanced by flowering but not affected by phenology, nor
by the F x P interaction (Table 1). In 1991, there were again significant flower, and F x Perfects (Table 2). This was due
primarily to the huge difference in survival rates between flowering (54.1%) and nonflowering (32.0%) branches on late
flushing trees (Fig. I).
Testing the grand means for cohorts I and 2 in 11989and 1991 revealed in both cases that survival was higher for the
first cohorts, but only statistically significant in 1989 (55% vs 43%).
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