1-(4-chlorophenyl)-3-(2,6-difluorobenzoyl)-urea when ingested by the last two larval instars of the spruce budworm, Choristoneura fumiferana, inhibits cuticle development leading to morphogenetic deformities in the pupal stage. Laboratory and greenhouse studies indicate that this material could be used to control natural populations of spruce budworm.

The 2-year-cycle spruce budworm, Choristoneura biennis Free. (Lepidoptera: Tortricidae), causes defoliation of spruce – subalpine fir forests in British Columbia, Canada. Historical and newly obtained data were used to develop a linear regression relating percent defoliation in the 2nd feeding year of the life cycle to the percentage of shoots damaged in the previous, 1st feeding year of the life cycle. The resulting regression was tested with independent data and correctly predicted (95% prediction intervals) defoliation in 14 of 15 stands. Patterns of defoliation were similar on white spruce, Picea glauca (Moench) Voss (Pinaceae), and subalpine fir, Abies lasiocarpa (Hook.) Nutt. (Pinaceae), and hence the regression can be used for either mixed or pure stands of either species.

A nuclear polyhedrosis virus has been isolated from the spruce budworm, Choristoneura fumiferana (Clemens) (Bergold, 1949; Bird, 1949; Bergold, 1951; Bird and Whalen, 1954; Bird, 1959), but no similar virus has been recovered from the jack pine budworm, Choristoneura pinus Freeman. Since these two species are very closely related (Smith, 1953) it was of interest to determine if C. pinus is susceptible to the C. fumiferana virus.

Responses were recorded of male spruce budworm (Choristoneura fumiferana (Clem.)) exposed to natural pheromone and a wide range of concentrations of synthetic pheromone in an all-glass wind tunnel equipped with a moving, patterned ceiling. The numbers of males wing-fanning and plume-following decreased with decreasing concentration of the pheromone plume. Speed of upwind flight with the ceiling stationary increased with decreasing concentration, but the durations of flight sustained by moving the ceiling were not significantly different under the different concentrations.

Males exposed to pheromone produced by calling females showed a higher incidence of plume-following, and flew significantly faster, than males exposed to a similar concentration of synthetic pheromone.

Bacillus thuringiensis Berliner is registered for control of several defoliating forest insects, including the spruce budworm (Choristoneura fumiferana Clem.), jackpine budworm (C. pinus Freeman), and gypsy moth (Lymantria dispar L.) (Morris et al. 1986). Product labels and user guidelines of several manufacturers recommend application to dry foliage for best results. Efficacy is presumably reduced when foliage is wet from dew or precipitation. Possible causes are lower impaction efficiency of spray droplets on the wet leaf surface (Spillman 1984) and dilution of the active ingredient. I compared the efficacy of B. thuringiensis applied to wet and dry balsam fir foliage (Abies balsamea L.) in a laboratory bioassay with larvae of the spruce budwom, Choristoneura fumiferana.

The spruce budworm, Choristoneura fumiferana (Clemens), is susceptible to a nuclear polyhedrosis virus and to a granulosis virus which may occur as single infections (Bergold 1950, 1951) or as double infections (Bird, 1959). Laboratory studies have shown that relatively heavy concentrations of either virus musr be injected or fed to hudworm larvae to cause infection and death. In one quantitative study Bergold (1951) estimated that the intralymphal LD50 of the polyhedrosis virus for the budworm is about 5000 times that for the silkworm, Bombyx mori L., when each is administered to its natural host. Field tests of the viruses were made in 1959 and 1960 to determine whether infection and mortality would result from spraying suspensions in infested forests.

Laboratory and field experiments indicate that the female spruce budworm (Choristoneura fumiferana (Clem.)) pupal stadium requires approximately 122C degree-days above a threshold of 7.2 °C (45°F), the male 124. Emergence time on any given day depends on temperature but is independent of photoperiod. Under field conditions male and female budworm mate only once per 24-h period. In the laboratory under continuous illumination females mate repeatedly and males readily mate a second time within a few hours, but the duration of the second copulation is abnormally long. The probability of multiple matings under field conditions is reduced by the restricted period of sexual activity coupled with the duration of copulation and the lower competitiveness of mated insects. Antennae are essential to the male for successful copulation.

Thuricide and Dipel, formulations of Bacillus thuringiensis (B.t.), were applied aerially against the spruce budworm, Choristoneura fumiferana (Clem.), in forest stands of balsam fir, Abies balsamea L. A dosage of 30 Billion International Units (BIU) of B.t./ha applied in 2.4 to 4.7 L of spray/ha was most effective. Application of 20 BIU/ha was marginally effective against a population of 12 to 36 larvae/45 cm of branch.

Benomyl or MBC phosphate incorporated into the meridic diet of eastern spruce budworm, Choristoneura fumiferana (Clem.), reduces the incidence of infection of adults by the microsporidian Nosema fumiferanae (Thom.). Some reduction in microsporidian levels is produced by 25 ppm benomyl; higher concentrations are more effective but even 250 ppm failed to reduce the incidence of microsporidia below 29% in a heavily infected stock. At benomyl concentrations of 75 ppm and above, budworm growth and fertility were reduced. The most notable effect of benomyl was the reduction of fertile matings and of percentage eclosion of eggs. Males were more sensitive to benomyl than females.

The effectiveness of Thuricide 16B®, a water-based commercial formulation of Bacillus thuringiensis var. torstaki (B.t.), Dipel 88®, an oil-based formulation, and the Dipel® vehicle (Dipel 88 without B.t.) were compared by aerial applications against the spruce budworm, Choristoneura fumiferana (Clem.) in balsam fir, Abies balsamea (L.) stands. The two B.t. products applied at similar dosage rates were similar in effectiveness and the Dipel vehicle was not toxic for budworm larvae at rates applied Comparisons of populations of parasites made between pre- and post-spray sampling periods and between treated and untreated plots indicated no direct effect of Dipel 88 on the rate of larval and pupal parasitism.

At a constant temperature of 1 °C, survival of diapausing second-instar larvae of C. fumiferana (Clem.) for any given period is, to a large extent, determined by pre-storage treatment. At a pre-storage temperature of 20 °C larval survival was 80% or higher following storage periods ranging from 169 to 290 days. Survival of larvae pre-stored at 24 °C was never as high as at 20 °C, and the survival began to decrease after 225 days storage. At 28 °C this decrease had occurred before 169 days of storage. Larvae held at high pre-storage temperatures had almost normal survival when the pre-storage period was shorter. Mean time for larvae to emerge from diapause was increased by longer diapause periods and by high pre-storage temperatures. There was a corresponding decrease in larval vigour.

Four different types of insect viruses have been isolated from the eastern spruce budworm, Choristoneura fumiferana (Clem.), but most research efforts have been concentrated on developing the nuclear polyhedrosis virus (NPV) as a viable control agent (Cunningham 1985). There are no published reports of LD50 values for this important forest pest. Recently, a LC50 of 483 viral polyhedra per square millimetre of diet surface for fifth-instar budworm larvae was determined using surface contamination feeding techniques (Cunningham et al. 1983). Because the dosages used in efficacy trials are derived from laboratory LD50 values, experiments were conducted to determine the virulence of this NPV to eastern spruce budworm. Bioassays were conducted with all feeding instars. Reported here are values for the LD50 dosages for third-, fourth-, fifth-, and sixth-instar spruce budworm larvae.

Supercooling point, biochemical metabolites, and water content of the larvae of Choristoneura fumiferana (Clem.) were measured during pre-diapause and diapause development under laboratory conditions. Supercooling point dropped significantly, from a mean value of −22.9 °C to −31.7 °C during the 3-week pre-diapause development. Supercooling point continued to decline down to −34.5 °C after the beginning of diapause. Water content also dropped significantly during pre-diapause development and was maintained at a low level during diapause. Significant amounts of glycerol were detected only when the larvae were 5 weeks into diapause and the glycerol level continued to increase until week 20 when it was almost 10 times its original level. Glycogen was nearly depleted after diapause, but lipid remained at a relatively high level. Little change in glucose and trehalose content was found during diapause in spite of their initial rise before diapause. Larvae could survive low temperatures close to their supercooling point without freezing but none survived freezing, suggesting that this species is freeze-intolerant. First-instar larvae were found to excrete green material out of their body within 5 days after emergence. Removal of this material from the insect body coincided with a significant drop in supercooling point, indicating that a potential nucleating factor might be involved in the green material. The implications of these results for the overwintering strategy of C. fumiferana are discussed.

Annual population estimates of spruce budworm, Choristoneura fumiferana (Clem.), larvae and the incidence of larval parasitism were monitored in northern New Brunswick following the collapse of the 1949–1959 epidemic in the region. The most common parasitoid among the very sparse hosts was Synetaeris tenuifemur, although it had been rarely found during the epidemic. Larval parasitism sometimes exceeded 50% but it could not be shown as a key factor associated with changing host abundance.

A series of low-volume spray treatments were conducted to study the contact and residual effect of two concentrations of the insecticide phosphamidon to fourth instar spruce budworm, Choristoneura fumiferana (Clem.), on balsam fir, Abies balsamea (L.) Mill, and red spruce, Picea rubens Sarg. Treatment of sprayed larvae on sprayed trees, unsprayed larvae on sprayed trees, and sprayed larvae on unsprayed trees, resulted in two principal conclusions: (a) Higher concentrations of phosphamidon (1% versus 0.5% active) accelerated mortality in all instances and (b) no statistical difference (P = 0.1%) was found in the final mortalities between treatments in which only the foliage was treated and where both larvae and foliage were treated with phosphamidon.

Laboratory wind tunnel and field observations have demonstrated an important behavioural role of tetradecanal (14:Ald) in the chemical communication system of the spruce budworm, Choristoneura fumiferana (Clemens). A greater number of males initiated upwind flight and continued on to contact the source when 14:Ald was present than with 95/5 E/Z11-tetradecenal (E/Z11-14:Ald) alone. The presence of E11-tetradecen-1-ol acetate (E11-14:Ac) decreased the males' responsiveness to the aldehydes. Its effect appeared to be attenuated, when present at low levels with 95/5 E/Z11-14:Ald, by the presence of 14:Ald, but it is still unclear what effects low levels of E11-14:Ac have on male behaviour.

The relationship between temperature and pathogenesis of Bacillus thuringiensis Berliner var. kurstaki in infected larvae of the eastern spruce budworm, Choristoneura fumiferana Clem., was investigated to determine if more rapid death of larvae with an increase in temperature could be accounted for by enhanced bacterial growth. Cumulative mortality of larvae force-fed with a lethal dose of HD-1-S-1980 peaked within 2 days at 25 °C, 3 days at 19 °C, 7 days at 16 °C, and 21 days at 13 °C. The progress of bacterial growth in the larvae was followed from spore germination to cell lysis, and was completed within 4 days at 25 °C, 6 days at 22 °C, 12 days at 19 °C, 14 days at 16 °C, and > 28 days at 13 °C. Peak abundance of vegetative cells in the larvae was observed after 1 day at 25 °C, 2 days at 22 °C, 3 days at 19 °C, 7 days at 16 °C, and 21 days at 13 °C, and thus coincided almost exactly with the time required for maximum larval mortality. This correlation suggests that the observed effect of temperature on progression of larval mortality was due to its effect on the proliferation of vegetative cells in the infected larvae, and that bacterial septicemia makes an important contribution to death.

Traps baited with a 95:5 blend of E:Z-11-tetradecenal, the sex pheromone of the spruce budworm, Choristoneura fumiferana (Clem.), were deployed throughout several summers in Ontario to determine what other Lepidoptera were captured that might be confused with the male C. fumiferana. Eight other species of Tortricidae were captured with sufficient frequency to suggest that they were attracted to the traps: Choristoneura conflictana Wlk. (the large aspen tortrix), six species of Acleris, and one Gretchena species. Of these, C. conflictana can easily be confused with C. fumiferana. The evidence suggests that male C. conflictana were not attracted by the pheromone, but blundered into the traps. They are very similar morphologically to male C. fumiferana, but can be differentiated with care.

Earlier attempts to correlate spruce budworm, Choristoneura fumiferana (Clem.), outbreaks and weather conditions were usually carried out by comparing seasonal data and spruce budworm outbreak development in broad terms: it was found that warm, dry weather favored outbreak development, while cool, wet weather retarded development. In this paper, laboratory experiments and historical data are examined to determine the effect of temperature and precipitation on second-instar larvae, just prior to and after spring emergence. Results tend to show that prolonged rain and freezing temperatures during and shortly after emergence are detrimental and may, in some cases, have a profound impact on outbreak development.

Field trials in northern Ontario in 1990 and 1991 confirmed that survival of spruce budworm larvae [Choristoneurafumiferana (Clemens)] (Lepidoptera: Tortricidae) parasitized by Apanteles fumiferanae Viereck (Hymenoptera: Braconidae) was greater than survival of nonparasitized budworm larvae following application of Bacillus thuringiensis var. kurstaki Berliner (Bt). Apparent parasitism by A. fumiferanae increased slightly when application of Bt was early (instar III or IV) but increased significantly when applications were later in the season (instars IV–VI). Delaying the timing of the spray conserved parasitoids while providing significant reductions in budworm densities and not compromising the primary objective of Bt application, i.e. the protection of current year foliage. The potential for long-term management of spruce budworm through the strategic integration of natural and imposed mortalities is discussed.