Intratree Variation in the Seasonal Distribution and Mortality of Spruce Budworm (Lepidoptera: Tortricidae) from the Peak to Collapse of an Outbreak

Abstract

A 5-yr field study was carried out to assess intratree variations in the distribution, abundance, and mortality of immature spruce budworm (Choristoneura fumiferana Clemens) (Lepidoptera: Tortricidae) from the peak to collapse of an outbreak. In most years, the highest density of overwintering second-instar (L2) larvae (per square meter of foliage) was located in the lower crown, whereas all subsequent stages (third-to sixth-instar larvae, pupae, and eggs) were at relatively higher densities in the upper crown. In contrast, overall abundance (per branch) throughout the season tended to be highest in the mid-upper to mid-lower crown. Mortality associated with 16 different parasitoid species varied significantly among years but varied among crown levels for only a few species. In particular, Apanteles fumiferanae (Viereck), Glypta fumiferanae (Viereck), Smidtia fumiferanae (Tothill), and Trichogramma minutum (Riley) all caused higher mortality in the upper crown of trees. Although infection associated with Nosema fumiferanae (Thomson) and mortality associated with fungal and viral pathogens often varied among crown levels, there was no clear or consistent trend from year to year. In general, trends in spruce budworm density and mortality within the crown were similar throughout all years of our study, despite significant variations in herbivore density, foliage availability, and parasitoid and pathogen impact. Our study indicates that intratree patterns of spruce budworm distribution and mortahty are likely to remain consistent during an outbreak and further emphasizes the importance of intratree heterogeneity in shaping interactions within plant-herbivore-parasitoid communities.

Spatiotemporal variation in drivers of parasitoid metacommunity structure in continuous forest landscapes

“…It is known that the spruce budworm parasitoid community changes through time and that different species attack different developmental stages of the host (Eveleigh and Johns 2014). Because of these temporal changes, species involved in consecutive parasitoid communities may be affected by different environmental features.…”

“…). The parasitoid community also varies in composition within a single season due to differences in parasitoid species phenology (Eveleigh and Johns , Seehausen et al. ).…”

Climate change effects on red spruce decline mitigated by reduction in air pollution within its shrinking habitat range

“…In particular, logging could be an important factor to understand red spruce ecosystem in GSMNP between 1940and 1979(Harmon et al, 1984. Also, red spruce is consumed by several insects (Eveleigh and Johns, 2014;MacKinnon and MacLean, 2004). However, no research has found a specialized relationship among the insects and logging and red spruce growth declines in the GSMNP.…”

Projection of red spruce (Picea rubens Sargent) habitat suitability and distribution in the Southern Appalachian Mountains, USA

“…This could be due to factors such as dispersal, competition between co-existing species, human disturbance by logging, and physical environmental conditions not considered in ARIM.SIMs due to the lack of literature information. For example, red spruce is consumed by several insects, such as spruce budworm (Choristoneura fumiferana) (Eveleigh and Johns, 2014;MacKinnon and MacLean, 2004), hemlock looper (Lambdina fiscellaria) (Alfaro et al, 1999). However, no research has found a specialized relationship between the insects and red spruce in the GSMNP.…”