Modeling the dynamics of mountain pine beetle aggregation in a lodgepole pine stand

Abstract

At least once a year the mountain pine beetle searches for lodgepole pines that provide a suitable habitat for a new brood. After attacking females feed, they produce an attractant pheromone that causes beetles to aggregate and, during outbreaks, to usually mass attack the "focus" tree. Near the completion of mass attack, incoming beetles are repelled and initiate attacks on adjacent "recipient" trees. An understanding of this "switching" process is useful for prescribing measures that minimize beetle damage.A mathematical model was developed to (1) describe beetle aggregation, (2) predict the relation of tree susceptibility and switching to changes in beetle density, (3) provide a structure for current knowledge, and (4) pose questions for further research. The model indicates that a high population density ensures mass aggregation and consequently successful tree colonization and switching. The model also indicates that the number of beetles attracted per attacking beetle differs from tree to tree, possibly depending on resin quality and production and/or the local flying density of beetles. Field and model results indicate that tree size appears to affect the repellence of beetles, suggesting that the attack density or the visual attractiveness of large trees is a factor. Further research could be directed at our assumptions on host resistance, repellence, pheromone emission rates, threshold concentrations, navigation, and pheromone dispersion.

Impact of Forest Fragmentation on Patterns of Mountain Pine Beetle-Caused Tree Mortality

“…Less patchy forests that contain a continuous spatial distribution of potential hosts become more beneficial at this stage as resource availability is higher and more easily accessed. When beetle populations reach the stage of an outbreak, beetles should prefer non-fragmented forests because of the cost of dispersal: beetles typically fly short distances to new hosts-approximately within 3-4 kilometres [56]-while only a small proportion of beetles engage in long distance dispersal. Short distance dispersal is thus facilitated in non-fragmented landscapes where resource availability is high.…”

Attraction to pheromone sources of different quantity, quality, and spacing: Density-regulation mechanisms in bark beetleIps typographus

“…Arriving beetles may then colonize nearby patches, such as other parts of the tree or adjacent trees. Such "switching," where the attack first focuses on one tree but, in a few days, switches to other trees in the vicinity, has frequently been observed at high "epidemic" population densities both in Dendroctonusfrontalis (Coulson, 1979), D. ponderosae (Geiszler et al, 1980), and in I. typographus (J.M. Hoff, unpublished; O. Anderbrant et al, unpublished).…”

Dynamics of pheromone production and communication in the mountain pine beetle, Dendroctonus ponderosae Hopkins, and the pine engraver, Ips pini (Say) (Coleoptera: Scolytidae)

“…Once an optimum attack density (62 galleries per m2) is reached, aggregation is terminated by the production of high concentrations of the multifunctional pheromones exo-brevicomin and frontalin by males (Ryker and Rudinsky 1982;Ryker and Libbey 1982;Raffa and Ben-yrnan 1983;Borden et al 1987) and verbenone by intestinal and gallery inhabiting microbes of both sexes (Leufvén et al 1984;Borden 1989, 1990). This signals to conspecifics the unavailability of fresh resource and switches the attack to adjacent trees in the vicinity (Rudinsky et al 1974a;Geiszler and Gara 1978;Geiszler et al 1980;Ryker and Li bbey 1982;Ryker and Yandell 1983).…”