Effects of the Destruction of the Current Year's Foliage of Balsam Fir on the Fecundity and Habits of Flight of the Spruce Budworm

Abstract

When spruce budworm larvae emerge in the spring, they either mine the needles of old foliage or feed upon the freshly opened staminate flowers of balsam fir. As soon as the vegetative buds begin to expand, the larvae abandon the needle mines for this newer and more succulent growth. Later, when the pollen is shed, the staminate flowers are in turn abandoned in favour of new shoots. Usually, the larvae continue to feed on the new shoots until pupation. When this insect reaches epidemic proportions, however, the current year's growth is often totally destroyed prior to the completion of the larval stage. Late spring frosts have also been known to destroy, in part, or even completely, the shoots of the current year's growth. Under these conditions spruce budworm larvae must resort to feeding on old foliage.

Wing wear and body size measurements of adult spruce budworms captured at light traps: inference on seasonal patterns related to reproduction

“…In contrast, the heavy weight of females relative to their body size during the night of 15-16 July suggests that they were young at the time of capture, which implies a pulsed emergence of 'resident' females. Females captured at locations with 'early epidemic' SBW populations in QC in 2013 were smaller than those at locations with endemic populations in NB and NL (Table 2), which is consistent with previous reports of inverse density-dependence of body size and fecundity of females (Blais 1953;Morris 1963;Régnière and Nealis 2007). What is surprising, however, is that defoliation was low (<10 %) in the 'early epidemic' locations in QC, which suggests that reduced size and fecundity of females operates on SBW population dynamics early in the transition phase between endemic to epidemic populations.…”

Population dynamics of the major North American needle-eating budworms.

“…Step Equation ( , 1980; B, 1981 and 1982; C, comparison, 1980 and 1981-82. 4.6.3.3 Differences across years~Using data from Kirkbride and Wagner (1983), Sheehan and others (1989) (Blais 1953, Greenbank 1956, Jaynes and Speers 1949, Miller 1957 by Miller (1963a Assuming a mean maximum fecundity of 200 eggs for the western budworm, an adult sex ratio of 1:1 (Campbell and others 1983c), and an average of about 40 eggs per mass (table 3), immigration of gravid moths clearly exceeds the combined effects of emigration and adult mortality when SA rises above about 2.5 egg masses per emerging moth. Average values of S A greater than 2.5 were found in every area used in this study during at least one year (figs.…”

“…Partially in consequence, defoliation in both areas had been severe for several years in succession. Significantly, both Blais (1953) and Sanders and Luc.uik (1975) presented laboratory data suggesting that starved eastern budworm females may disperse before ovipositing. Several authors have noted that adults of eastern budworm fly away from defoliated stands, presumably because these trees lack adequate oviposition sites (Blais 1953, Morris 1963b).…”

“…Significantly, both Blais (1953) and Sanders and Luc.uik (1975) presented laboratory data suggesting that starved eastern budworm females may disperse before ovipositing. Several authors have noted that adults of eastern budworm fly away from defoliated stands, presumably because these trees lack adequate oviposition sites (Blais 1953, Morris 1963b). Palanaswamy and Seabrook (1978) provide evidence that "Female moths may be capable of using pheromone concentration to assess population density and thus may be stimulated by the pheromone to lay a portion of their eggs and disperse.…”

The Role of Climate and Dispersal in the Initiation of Outbreaks of the Spruce Budworm in New Brunswick: I. The Role of Climate

“…The importance of food quality to the fecundity of the spruce budworm has been demonstrated by several i~ivestigators (5,14 in their later larval stages, have beell forced to feed on foliage of previous years. Experiments 1i1ei-e conducted a t Green River to determine whether the food quality of current foliage also deteriorates as the season progresses.…”