During the course of genetic studies on the spruce and jack pine budworms, it was noted that there are distinct morphological characters on which the pupae and egg clusters may be separated. They are described here as a contribution towards the taxonomic separation of Choristoneura fumiferana (Clem.) and C. pinus Free.

A rapid means of identifying species of insects on the basis of physical measurements is useful to the field worker. The efficiency of the postclypeal index in separating the larvae of two closely allied species is illustrated herein. Occasionally species fall into overlapping subgroups, making it difficult to determine the characteristics of a given subgroup. A method useful in identifying such subgroups is outlined herein.

All stages of the spruce budworm parasite Glypta fumiferanae (Viereck) are described in this paper. Illustrations of all stages are presented.

The spruce budworm, Choristoneura (Archips) fumiferana (Clem.) (Tortricidae) has long been considered one of the most injurious forest insect pests in Canada. A general account of past outbreaks and an outline of its biology and bahits are given by Swaine and Craighead (1924). At the time these studies were made investigations were also undertaken by J.D. Tothill and A.B. Baird on the parasites and other natural control factors of the spruce budworm, but although a good deal of work was done, brief reference to which is made by Hewitt (1911, 1912, 1913), very little has been published.

The impacts of insect outbreaks on tree mortality, productivity, and stand development in Canada are reviewed, emphasising spruce budworm (Choristoneura fumiferana (Clemens), Lepidoptera: Tortricidae) and mountain pine beetle (Dendroctonus ponderosae Hopkins, Coleoptera: Curculionidae). Reduced growth and survival are a function of insect population and defoliation level. It is feasible to make short-term (annual) predictions of insect population and defoliation based upon sampling, but long-term, multi-year predictions are problematic. Given the historical record, it is expected that outbreaks will occur with relatively predictable frequency and basic host relationships and abiotic constraints will not change dramatically. However, the precision of predictions at fine scales is variable and reduced over time. Relationships between tree growth reduction, survival, and cumulative defoliation or beetle population level are available for major insect species. Understanding insect outbreak effects hinges on mortality, changes in interspecies competition, regeneration, and succession. Altered stand dynamics caused by insects can be interpreted for indicators such as wildlife habitat, old forest, riparian buffer cover, viewscapes, and connectivity. Anthropogenic changes are altering impacts via range expansions, northward shifts, and changes in forest composition. We can better understand effects of insect outbreaks and how best to ameliorate damage through a combination of empirical permanent plot studies, modelling, and manipulative experiments.

Most emerging 2nd-instar larvae of spruce budworm, Choristoneura fumiferana (Clem.), tested in the laboratory were photopositive and there was no difference in response between healthy larvae and larvae parasitized by Apanteles fumiferanae Vier. However, in the field, parasitized individuals were under-represented among larvae dispersing on silk threads between tree crowns. There is evidence that this was due to the relatively late emergence of parasitized larvae. These parasitized larvae therefore encountered fewer crawling larvae at the tips of branches, and consequently their propensity for dispersing was reduced.

The vertical distribution of dispersing, parasitized larvae caught on sticky traps more closely resembled that of established larvae than it did the vertical distribution of the overwintering population. This indicates that there was some differential redistribution of parasitized and nonparasitized individuals. Despite these differences, the estimate of parasitism by A. fumiferanae based on mid-crown branch samples is justified because it is most consistent and most closely reflects the overall frequency of parasitism.

Although the spruce budworm, Choristoneura fumiferana (Clemens), has received much attention as a result of its economic importance, little is known about its internal morphology and development. In this paper some features of the embryonic development will be described and compared with those of other Lepidoptera.

A number of ketocatechols have been isolated and identified from acid hydrolysates of larval and pupal exuviae of the spruce budworm, Choristoneura fumiferana. The most abundant of these, 2-hydroxy-3′,4′-dihydroxyacetophenone, represented 5.8% of the dry weight of pupal exuviae, 4.6% of larval head capsules, and 0.3% of the remaining larval exuvium. This compound is thought to be the primary breakdown product arising from crosslinks between cuticular proteins and the aliphatic sidechain of a phenolic tanning compound. The yields therefore reflect the extent of β-sclerotization, one of two mechanisms proposed for the hardening of insect cuticle. Budworm is similar to other species with respect to the types of hydrolysis products recovered although three previously undescribed compounds were detected.

Bacillus thuringiensis was applied at three dosages (1.0 BIU/tree, 0.1 BIU/tree, and.01 BIU/tree) to balsam fir, Abies balsamea (L.) Mill., and white spruce, Picea glauca (Moench) Voss, with mist blowers. Crystalline proteins were detected on balsam fir foliage for a maximum of 16 days (d) after B. thuringiensis was applied at 1.0 BIU/tree. Higher levels of crystalline proteins were detected on white spruce foliage treated with Thuricide 16B than on that treated with Dipel 4L. On balsam fir, the situation was the opposite. Mist-blower-treated foliage collected for up to 16 d posttreatment caused mortality of spruce budworm, Choristoneura fumiferana (Clemens), larvae. Viable endospores of B. thuringiensis were recovered on white spruce foliage collected 1 year after treatment.

Field trials were conducted in British Columbia and Oregon in 1972, which demonstrated that trans-11-tetradecenal, a sex attractant for male Choristoneura fumiferana and C. occidentalis, is also a sex attractant for male 2-year-cycle spruce budworm, C. biennis, and that trans-11-tetradecenyl acetate is a sex attractant for male green budworm, C. viridis Free.

Adults of Choristoneura fumiferana, C. biennis, and an unidentified species reared from larvae or caught in pheromone traps from British Columbia were used for isozyme analysis to confirm the species identity, and for morphological study to determine the percentage of individuals with spiculate aedeagi. About 82% of C. fumiferana and less than 3% of both C. biennis and C. unidentified species (CPG) have spicules on the left side of their aedeagi. The number of moths that need to be sampled to determine a species is presented, based on the presence or absence of spicules.

Infection by Nosema fumiferanae (Thomson) (Microsporidia: Nosematidae) and feeding by late-instars on previous year’s foliage due to depletion of current year’s growth (also known as back-feeding) are likely to co-occur in high-density outbreak populations of the spruce budworm (Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae)). We tested the hypothesis that effects of the two factors on larval fitness are exacerbated by their interaction. Twigs of balsam fir (Abies balsamea Linnaeus; Pinaceae) with or without new-growth shoots were fed to sixth-instar offspring from uninfected, moderately infected, or highly infected females in two laboratory experiments. Pupal mass and time to reach the pupal stage were significantly affected by infection and back-feeding but not by their interaction. Pupal mass decreased and development time increased with increasing spore burden in a linear fashion. Back-feeding had a significant effect on survival to the pupal stage, but infection did not, nor did their interaction. The relatively small changes in survival, pupal mass, and development time caused by infection and back-feeding were additive. The results thus refute our hypothesis that infection by N. fumiferanae and forced feeding on last year’s foliage by late instars are likely to interact in affecting spruce budworm recruitment in older outbreak populations.

The host range of a mixture of Choristoneura fumiferana (Clemens) nucleopolyhedroviruses (CfMNPV and CfDefNPV) was investigated using a per os bioassay of larvae of 29 species of Lepidoptera and adult males of Megachile rotundata (F.) (Hymenoptera: Megachilidae). Using a whole-genomic DNA probe, positive results were obtained in 8 of 10 Tortricidae: Archips cerasivorana (Fitch), Choristoneura fractivittana (Clemens), C. fumiferana, Choristoneura occidentalis Freeman, Choristoneura pinus pinus Freeman, Choristoneura rosaceana (Harris), Clepsis persicana (Fitch), and Cydia pomonella (L.); one Crambidae: Ostrinia nubilalis (Hübner); one arctiine Erebidae: Estigmene acrea (Drury); and two Noctuidae: Oligia illocata (Walker) and Pyrrhia exprimens (Walker). Mortality rates were highest among C. fumiferana, C. occidentalis, C. pinus pinus, A. cerasivorana, and C. pomonella. Sequenced polymerase chain reaction (PCR) amplicons from infected individuals from several species confirmed that the primer sets amplified the target viruses. CfMNPV was consistently found in virus-fed C. fumiferana; whereas, CfDefNPV was present only occasionally. The presence of CfMNPV and CfDefNPV in A. cerasivorana was confirmed by PCR and DNA sequencing. Significant treatment-mortality rates were induced in the noctuids P. exprimens and Acronicta impleta Walker; PCR determined that both viruses were present in treated P. exprimens but only CfMNPV was present in A. impleta. No virus was detected in M. rotundata.

Requirements for diapause development of larvae of Choristoneura fumiferana have been generally believed to be met by temperatures of 2°C or below for a period ranging from 14 to 20 weeks (see review by Sanders 1991), whereas those favourable for post-diapause development were shown to be above 11°C (Régnière 1990). However, we noticed that a large number of larvae completed diapause after 10 weeks at 18°C without any cold storage. The following experiment was carried out to confirm this result.

Annual catches of male spruce budworm (Choristoneura fumiferana [Clem.]) in sex pheromone traps over a 21-year period in northwestern Ontario were well correlated with larval population densities in each subsequent year (r2 = 81%). On the basis of the criterion of 3 successive years of increasing catches or a threshold of 50 moths per trap, warning of extensive defoliation could have been given 6 years in advance. In 18 plots in northwestern Ontario and 35 plots distributed throughout the province, coefficients of determination (r2) between catch and population density in the same generation ranged from 40 to 74% in 1982 and 1983, but fell below 23% in 1984 when population densities in many plots were high. Coefficients of determination between catch and population densities in the following generation (eggs or larvae) ranged from 41 to 62%. On the basis of several years of cooperative research, sex pheromone traps are now in operational use in eastern North America for monitoring spruce budworm populations.

At least two species of parasitic larval mites of the erythraeid genus Leptus were found on male spruce bud worm, Choristoneura fumiferana (Clem.), moths attracted to pheromone-baited traps. Mites were found on 28.5% of 2298 male moths captured during three trapping days in July 1977. Numbers of mite-infested moths were positively correlated with catch density. Percentage mite infestation increased with time. Red larval mites were also collected from both male and female free-flying budworm moths. Attachment sites include: wing veins, cervix, compound eye, femur, and abdomen. As many as four mites were collected from one female moth.

Coincident populations of spruce budworm, Choristoneura fumiferana (Clem.) and spruce coneworm, Dioryctria reniculelloides (Mutuura and Munroe) were studied to compare spatial distribution, temporal abundance, relative abundance on spruce species, and the relative efficacy of aerial insecticide treatments.Most individuals of both species were found overwintering on the mid-crown branches of red spruce, and a whole branch is a suitable unit for simultaneous sampling of overwintering budworm/coneworm populations on red spruce. Survey records since 1949 show similar geographical and temporal population trends for these 2 insects in Maine. A correlation analysis (r = 0.87) indicates that the size of their coincident populations is related spatially. Both species were found overwintering in nearly equal proportions on red and white spruce sampled from the same stands. But twice as many budworm and coneworm were found overwintering on red spruce when red and black spruce were sampled on the same stands. Due to behavioral or physiological traits the coneworm appeared resistant to aerial spray treatments that significantly reduced budworm populations.

Concerning the light reactions of the adults, it may be noted that males are photopositive when in a dark-adapted state, but they rapidly become adapted to any light intensity and become extremely sluggish. Females in the dark-adapted state exbihit either photonegative behaviour or compassing behaviour, with no evidence that there is any orderly transition from one type of behaviour to the other. Light-compass orientation of flying females makes it possible to collect some at light traps, despite their normally negative response.

I conducted dual-choice oviposition bioassays to test the hypothesis that spruce budworm, Choristoneura fumiferana (Clemens), prefer the foliage architecture (spatial arrangement of foliage needles) of white spruce (Picea glauca (Moench) Voss; Pinaceae) to that of balsam fir (Abies balsamea (L.) P. Mill.; Pinaceae). Needles of white spruce radiate around the twig axis, giving the foliage a round architecture. Needles of balsam fir typically radiate bilaterally from the twig axis, giving the foliage a flat architecture, although on some trees foliage needles radiate around the twig axis, giving the foliage a round architecture. In bioassays, females showed a 2.4:1 preference for white spruce over "flat" balsam fir foliage, but this preference was reduced significantly to a 1.2:1 ratio when balsam fir had a round architecture. Given a choice between "round" and "flat" balsam fir foliage, females preferred the "round" foliage by a 2.2:1 margin. A similar preference for the round architecture was also observed when artificial (plastic) foliage with the two types of needle arrangements were compared. I conclude that the spatial arrangement of foliage needles is a major factor responsible for the oviposition preference of spruce budworm for white spruce over balsam fir.

During the past decade a severe outbreak of budworm has been in progress on jack pine in northwestern Ontario, following similar infestations in Michigan and Minnesota. It has been observed that budworm on jack pine does not spread to adjacent stands of balsam fir and spruce, and similarly that outbreaks on fir and spruce do not spread to adjacent jack pine stands.