Program
| MSC2d | |
|---|---|
| Jacques Régnière | |
| Laurentian Forestry Centre, Canada Forest Service | |
| Title | Comparative Empirical Models of Local Population Dynamics for Three Conifer-Feeding Budworms |
| Abstract | We have been working on a comparative modeling approach to the dynamics of three damaging species of conifer-feeding budworms (Choristoneura fumiferana, the eastern spruce budworm; C. occidentalis, the western spruce budworm; and C. pinus pinus, the jack pine budworm). Over the years, a large amount of population data has amassed and an overall understanding of their dynamics has crystallized. These three species share very similar life systems, yet exhibit very different outbreak dynamics. Our explanation focuses on the differences between species in the intensity of the feedback between defoliation and population performance, around a concept that call the Risk of Dispersal. This is an empirical modeling approach, of course, which makes for simple math but very complex (messy) systems. These models are intended to describe the essential aspects of population dynamics of the three budworms All three budworm species are univoltine, with discrete generations. All three undertake two larval dispersal phases. In the fall, they leave the egg mass laid on host foliage in search of overwintering sites (anywhere in the stand). They spend winter in the 2nd instar. In the spring, they must disperse again to find host foliage and start feeding. They all undergo a total of 6 larval stages. They share the same (or very similar) natural enemy complexes and are exposed to much the same environmental factors. It is in the details of their relationships with their host plants that they differ most. Jack pine budworm cannot mine old needles of its host prior to bud break in the spring. It therefore requires the presence of staminate flowers to survive until succulent foliage is available. Western spruce budworm can mine old needles of its main host, Douglas fir. But it requires adjacent needle pairs to do so. Thus, past defoliation greatly decreases survival during the needle-mining period. Eastern spruce budworm is much less fussy: it will readily accept to mine old needles, or staminate flowers, on either of its main hosts (balsam fir and white spruce). However, once trees start dying from severe defoliation, it become increasingly risky to disperse in search of food. Our discrete, empirical models integrate available knowledge in an attempt to account for differences in the frequency, intensity and duration of outbreaks of these three species. This is the first step, before these models are placed in a spatial context where movement between populations can be included. |
| Location | Friedman 153 |