Spruce Beetle Population Suppression in Northern Utah

The spruce beetle is a widely dispersed, native bark beetle that attacks and kills North American spruces. We describe aproject that was initiated to suppress an endemic spruce beetle population in an isolated 1000 ac area of spruce in northeastern Utah. Techniques used included baited pheromone traps, selective harvesting and burning of infested trees, and trap trees. Over the 3 yr period of monitoring, the number of standing, currently infested spruce trees was reduced 91%. FieM surveys and data trends, in comparison with a nearby spruce beetle population that continued to increase, indicate that the treatments played a major role in decreasing the trend of spruce beetle-infested trees during the study period. This combination of suppression techniques was successful due to the isolated nature of the spruce stands, early detection of the beetle population, accessibility of the stands, and coordinated efforts of local, state, and federal agencies. West. J. Appl. For. 15(3):122-128. The spruce beetle (Dendroctonus rufipennis), a native bark beetle associated with North American spruces (Picea spp.), is widely distributed throughout North America. The beetle' s range follows that of its host from Alaska southward along the Rocky Mountain range into eastern Arizona and western New Mexico and across the Canadian provinces into northeastern United States (Wood 1982). In general, spruce trees tend to be shallow-rooted with little windfirmness and consequently are prone to blowdown (Alexander 1986). The spruce beetle takes advantage of this particular aspect of its host behavior, preferentially attacking downed trees to live standing ones. As population levels increase, however, live standing spruce may also be attacked in large numbers, resulting in widespread tree mortality over expansive acreNOTE: B.J. Bentz is the corresponding author and can be reached at (435) 755-3560; Fax: (435) 755-3563; E-mail: bbentz@fs.fed.us. Chuck Frank (silviculturist), Dwayne Bell (forestry technician), Evelyn Sibberson (forester), and Kent O'Dell (timber management coordinator) with the Wasatch Cache National Forest, and Jim Long with Utah State University were instrumental in the success of this project. Discussions with Pat Shea provided insight into funnel trap placement. The authors thank field crews from Forest Health Protection, Ogden, UT; Department of Forest Resources-Utah State University; and the Rocky Mountain Research Station, Logan, UT, for help with the extensive surveys. Tom Bradley was responsible for GPS measurements and GIS analysis. Jim Long, Ed Holsten, and an anonymous reviewer provided valuable input to the manuscript. This article reports the result of research only. Mention of a proprietary product does not constitute an endorsement or a recommendation by the USDA Forest Service for its use. Pheromones used in this study are not currently registered for use by the general public. Caution should be used when pheromones are deployed in a forest setting to avoid undesirable tree mortality. A qualified state or federal entomologist should be contacted for advice on the use of bark beetle pheromones. ages (Schmid and Frye 1977). In northern Utah, spruce beetles emerge from brood trees and disperse to attack new hosts between May and late July when temperatures reach approximately 16oC (Dyer 1973). Throughout i s host range, populations typically require 2 yr to complete a generation, although generation time depends greatly on temperature (S afranyik and Linton 1999, Werner and Holsten 1985, Bentz and Hansen unpublished ata) and may require as little as 1 yr or as long as 3 yr. In 2 yr populations, brood emerge the second summer after a tree has been attacked. One strategy for managing spruce beetle populations is the use of trap trees. This method takes advantage of the tendency for spruce beetles to attack downed trees. Larger diameter, green spruce are felled into the shade and left unbucked and unlimbed (Hodgkinson 1985, Nagel et al. 1957). Trap trees typically have greater mean attack densities than standing spruce (Schmid and Frye 1977) and can absorb as many as 10 times the number of beetles (Wygant 1960, unpublished). In areas with lower infestation levels, one trap tree is cut down for each four to five infested standing trees, with no more than 1/4 mi between an infested group of trees and the trap trees. When feasible, legal, and accessible, trap trees may be injected with a translocating silvicide to eliminate the need for trap tree removal or brood destruction through debarking or burning (Gray et al. 1990, Lister et al. 1976). Otherwise, infested trap trees must be removed from the stand, burned, or buried before the next beetle flight to avoid a localized increase in the beetle population. In areas that are accessible by road, sanitation-salvage logging of infested trees before beetle flight is a recommended treat-