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.

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.

Abstract-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.

Longhorn beetles are among the most important groups of invasive forest insects worldwide. In parallel, they represent one of the most well-studied insect groups in terms of chemical ecology. Longhorn beetle aggregation-sex pheromones are commonly used as trap lures for specific and generic surveillance programs at points of entry and may play a key role in determining the success or failure of exotic species establishment. An exotic species might be more likely to establish in a novel habitat if it relies on a pheromone channel that is different to that of native species active at the same time of year and day, allowing for unhindered mate location (i.e., pheromone-free space hypothesis). In this study, we first tested the attractiveness of single pheromone components (i.e., racemic 3-hydroxyhexan-2-one, racemic 3-hydroxyoctan-2-one, and syn-2,3-hexanediol), and their binary and tertiary combinations, to native and exotic longhorn beetle species in Canada and Italy. Second, we exploited trap catches to determine their seasonal flight activity. Third, we used pheromone-baited "timer traps" to determine longhorn beetle daily flight activity. The response to single pheromones and their combinations was mostly species specific but the combination of more than one pheromone component allowed catch of multiple species simultaneously in Italy. The response of the exotic species to pheromone components, coupled with results on seasonal and daily flight activity, provided partial support for the pheromone-free space hypothesis. This study aids in the understanding of longhorn beetle chemical ecology and confirms that pheromones can play a key role in longhorn beetle invasions.

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.