Factors Affecting Spruce Beetles during a Small Outbreak

Abstract

In 1957, spruce beetles, Dendroctonus rufipennis developed into outbreak numbers in logging slash at a north—central Colorado site, entered living spruce trees, but remaining epidemic for only two years. Reduced beetle fecundity was the first indication of outbreak decline; this was caused by nematodes and unknown agents. Significant summer mortality agents were pitch, intra— and interspecific competition for food, predation by woodpeckers and flies, and parasitism by wasps. Desiccation of both food and beetle larvae, enhanced by woodpecker feeding activity, contributed significantly to outbreak decline. Winter mortality was attributed mainly to woodpeckers, although temperature of —29°C caused additional losses. The effects of the outbreak on the spruce were considerable. Large diameter trees in small patches were killed, and species composition was altered in favor of subalpine fir and lodgepole pine, but mean tree diameter was not significantly reduced.

Ecosystem CO2/H2O fluxes are explained by hydraulically limited gas exchange during tree mortality from spruce bark beetles

“…Over the past two decades, spruce beetle has disrupted 1,500,000 ha of forest in Alaska and is currently infesting 166,000 ha in the western United States, with 84,000 ha in Colorado and 32,000 in Wyoming [USDA Forest Service, 2012]. Spruce beetle epidemics are not new to the Rocky Mountains [Dymerski et al, 2001;Love, 1955;McCambridge and Knight, 1972;Schmid and Frye, 1977;Veblen et al, 1991] but the potential for outbreaks is expected to rise under climate change [Bentz et al, 2010]. A warming climate facilitates spruce beetle population growth by quickening the insect's life cycle from semivoltine to univoltine FRANK ET AL.…”

Regulation of spruce bark beetles by woodpeckers—a literature review

“…The latter are thought to improve the efficiency of past and current beetle control programs and/or reduce management costs (Coulson, 1979;Reeve et al, 1995). In particular, a number of investigations have identified woodpeckers as major vertebrate predators of bark beetles which colonize conifers, especially in north America (Otvos, 1965(Otvos, , 1970McCambridge and Knight, 1972;Moore, 1972;Kroll et al, 1980). Aggressive pest management programs which involve extensive harvesting of beetle-infested stands and stands susceptible to infestation may negatively impact local woodpecker populations and, in turn, the potential of the co-evolved predators to participate in regulating bark beetle populations.…”

If Long-Term Resistance to a Spruce Beetle Epidemic is Futile, Can Silvicultural Treatments Increase Resilience in Spruce-Fir Forests in the Central Rocky Mountains?

“…Recent spruce beetle epidemics have probably been driven by a combination of factors including susceptible stand structure and composition coupled with widespread drought [20]. Spruce beetles favor large diameter (>25 cm diameter at breast height (dbh)) Engelmann spruce for both protection and nutrition [21,22]. Recent dry conditions in high-density stands increase stresses on individual trees, decrease growth rates, and decrease defenses against the beetle, allowing spruce beetle populations to rapidly increase [8,18].…”