Sara Edwards

Wild eastern spruce budworm (Choristoneura fumiferana Clemens) were reared on white spruce (Picea glauca (Moench) Voss) trees, half of which had been previously inoculated with a native endophytic fungus, Phialocephala scopiformis DAOM 229536 Kowalski and Kehr (Helotiales, Ascomycota). Survival up to pupation and up to adult emergence was approximately 27% higher for budworm juveniles that developed on control trees compared to trees inoculated with the endophyte. The endophyte did not influence the size or sex of survivors but did reduce defoliation by approximately 30%. Reductions in defoliation on endophyte-inoculated versus control trees, due to reductions in survival of juvenile budworms, suggests that tree inoculations with P. scopiformis could play an important role in integrated management programs against the eastern spruce budworm.

The spruce budworm, Choristoneura fumiferana, Clem., is the most significant defoliating pest of boreal balsam fir (Abies balsamea (L.) Mill.) and spruce (Picea sp.) in North America. Historically, spruce budworm outbreaks have been managed via a reactive, foliage protection approach focused on keeping trees alive rather than stopping the outbreak. However, recent theoretical and technical advances have renewed interest in proactive population control to reduce outbreak spread and magnitude, i.e., the Early Intervention Strategy (EIS). In essence, EIS is an area-wide management program premised on detecting and controlling rising spruce budworm populations (hotspots) along the leading edge of an outbreak. In this article, we lay out the conceptual framework for EIS, including all of the core components needed for such a program to be viable. We outline the competing hypotheses of spruce budworm population dynamics and discuss their implications for how we manage outbreaks. We also discuss the practical needs for such a program to be successful (e.g., hotspot monitoring, population control, and cost–benefit analyses), as well as the importance of proactive communications with stakeholders.

A manipulative field study was carried out to determine whether the foliar endophyte fungus, Phialocephala scopiformis DAOM 229536, decreased the performance of eastern spruce budworm, Choristoneura fumiferana larvae developing on white spruce trees. Overwintered second-instar budworm larvae from a laboratory colony or from a wild population were placed on endophyte positive or negative trees one or two weeks before budburst. The presence of the endophyte in the needles reduced the survival of C. fumiferana from both a wild population and a laboratory colony. Survival for budworm juveniles up to pupation and to adult emergence was 13% and 17% lower, respectively, on endophyte positive trees. The endophyte did not influence the size or sex of survivors and budworm survival was not influenced by any two- or three-way interactions. Budworm survival was higher for wild than for laboratory-reared budworm and for budworm placed on trees a week before budburst. This may be the first field study to demonstrate the efficacy of an endophytic fungus against wild individuals of a major forest insect pest. The efficacy of the endophyte at low larval densities suggests that it could be a useful tactic to limit spruce budworm population growth in the context of an early intervention strategy.

The use of fossil moth wing scales has recently been introduced as a new method to reconstruct population histories of lepidopterans and provide a proxy for insect disturbance. We investigated the potential for using wing-scale ultrastructure to distinguish between the five most common outbreak species of moth pests in eastern North America: spruce budworm ( Choristoneura fumiferana Clemens), hemlock looper ( Lambdina fiscellaria Guenée), forest tent caterpillar ( Malacosoma disstria Hübner), blackheaded budworm ( Acleris variana Fernie), and jack pine budworm ( Choristoneura pinus Freeman). Using scanning electron images of scales, we made qualitative and quantitative comparisons of morphological traits at the ultrastructural level. We found that hemlock looper and eastern blackheaded budworm scales could be categorically separated from each other and from the three other species. We developed a quadratic discriminant function using measurements of ultrastructure traits that distinguishes scales of the three remaining species with an overall accuracy of 66%. We found that forest tent caterpillar could be well separated based on these traits, but we were less confident in distinguishing the closely related jack pine and spruce budworm. Our method offers potential advantages in scale identification for future studies in paleoecology, while providing the additional advantage of not requiring intact, unfolded, and undamaged scales.

A two-year field study was carried out to determine whether inoculating white spruce, Picea glauca (Moench) Voss, with a native endophytic fungus, Phialocephala scopiformis DAOM 229536 Kowalski & Kehr (Helotiales, Ascomycota), decreased the performance of eastern spruce budworm, Choristoneura fumiferana Clemens, developing on these trees. Second instars were reared at three densities in the mid crown and at one density in the lower, mid, and upper crown. Larval survival (i.e., survival of larvae to pupation) was lower on endophyte-inoculated trees than on control trees in the mid crown and especially the upper crown but was similar in the lower crown, resulting in a significant interaction between endophyte and crown level. A similar but marginally insignificant interaction was observed for overall survival up to adult emergence (i.e., total survival). Larval survival and total survival were approximately 22% and 19% lower, respectively, when developing in the upper crown of endophyte-inoculated trees than in control trees. Larval survival remained relatively constant, with increased density on control trees but decreased with density on endophyte-inoculated trees, resulting in a significant interaction between endophyte and larval density. Sex ratios of emerged adults and wing lengths of emerged females were not influenced by the endophyte. Our results suggest that endophytic fungi could be useful additions to integrated pest management programs.

Many populations are thought to be regulated, in part, by their natural enemies. If so, disruption of this regulation should allow rapid population growth. Such “enemy escape” may occur in a variety of circumstances, including invasion, natural range expansion, range edges, suppression of enemy populations, host shifting, phenological changes, and defensive innovation. Periods of relaxed enemy pressure also occur in, and may drive, population oscillations and outbreaks. We draw attention to similarities among circumstances of enemy escape and build a general conceptual framework for the phenomenon. Although these circumstances share common mechanisms and depend on common assumptions, enemy escape can involve dynamics operating on very different temporal and spatial scales. In particular, the duration of enemy escape is rarely considered but will likely vary among circumstances. Enemy escape can have important evolutionary consequences including increasing competitive ability, spurring diversification, or triggering enemy counteradaptation. These evolutionary consequences have been considered for plant–herbivore interactions and invasions but largely neglected for other circumstances of enemy escape. We aim to unite the fragmented literature, which we argue has impeded progress in building a broader understanding of the eco-evolutionary dynamics of enemy escape.

Our review highlights research during the past century focussed on the population ecology of outbreak-prone insect defoliators in Canadian forests. Based on reports from national and provincial surveys that began in the 1930s, there have been at least 106 insect defoliators reported to outbreak, most of which are native Lepidoptera, Hymenoptera (sawflies), or Coleoptera (in order of frequency from most to least). Studies comparing life-history traits of outbreak versus non-outbreak species to better understand why certain species are more outbreak-prone indicate several traits especially common among outbreak species, including egg clustering and aggregative larval feeding. There have been at least 50 time-series studies examining the spatiotemporal population behaviour of 12 major defoliator species. These studies provide evidence for both regular periodicity and spatial synchrony of outbreaks for most major species. Life-table studies seeking to understand the agents causing populations to fluctuate have been carried out for at least seven outbreak species, with the majority identifying natural enemies (usually parasitoids) as the major driver of outbreak collapse. Our review concludes with several case studies highlighting the impact and historical underpinnings of population studies for major defoliator species and a discussion of potential avenues for future research.

We evaluated the effect of tree genotype on the resistance of balsam fir,Abies balsamea(Linnaeus) Miller (Pinaceae), to damage from the balsam twig aphid,Mindarus abietinusKoch (Hemiptera: Aphididae), by visually assessing aphid damage in clonal seed orchards located in New Brunswick and Nova Scotia, Canada, during four consecutive years. Estimates of clone mean heritability were moderate, suggesting that heritability of resistance is influenced by genetic factors. In New Brunswick, positive phenotypic and genetic correlations of clone-mean damage among years indicate that clones rank similarly each year. Our results suggest that selectively breeding for increased resistance could result in genetic gains.

Field surveys were carried out to assess the effects of intra‐tree variation in developing shoot length within and among crown levels on the density and abundance of the balsam shoot‐boring sawfly, Pleroneura brunneicornis Rohwer (Hymenoptera: Xyelidae), in young balsam fir, Abies balsamea (L.) Mill. (Pinaceae). Overall, cardinal direction had no influence on shoot‐borer density or abundance; however, the highest percentage and abundance of bored shoots occurred on intermediate‐sized shoots within the crown (i.e., in the mid‐crown and on the distal‐lateral and medial‐lateral shoots). Comparatively, few shoot borers occurred in the upper or lower crown levels, or on the relatively large terminal shoots within branches. This distribution appears indicative of the higher suitability of intermediate‐sized shoots within hosts for either egg lay or larval performance. Results of this study are most consistent with predictions of the ‘optimal module size’ hypothesis, which posits that herbivore responses to plant module size should reflect the balance of tradeoffs between utilizing relatively large, nutritious shoots vs. small, more easily exploited shoots.

Canada has a distinguished history of research in forest entomology. The number of peer-reviewed publications emanating from studies in forest entomology in Canada greatly increased following the Second World War. Much of the outstanding historical success in Canadian forest entomological research is attributable to the work of entomologists employed by the Canadian Forest Service, who authored the majority of studies until the mid 1970s and usually published them in The Canadian Entomologist. Since that time the majority of studies have been published by Canadian universities in a broad range of journals. Most early research in forest entomology in Canada was carried out by men, but since that time the proportion of forest entomological research carried out by women has increased significantly. The majority of research in central and eastern Canada focussed on defoliators and their natural enemies and host plants whereas the majority of research in western Canada examined bark beetles (Coleoptera: Curculionidae: Scolytinae) and their natural enemies and host plants. Although publications on defoliators and their natural enemies have occurred continuously throughout the historical development of forest entomology in Canada, the numbers of publications on wood borers (Coleoptera: Buprestidae, Cerambycidae) and bark beetles and their natural enemies have never been higher than they are presently.