The spruce beetle, Dendroctonus rufipennis, can cause extensive mortality of Engelmann spruce, Picea engelmannii, during outbreaks. Endemic populations breed in the underside of downed spruces. Outbreaks often develop after blowdowns that create abundant downed trees where beetle populations can increase. Occasionally, managers practice suppression to protect high-value resources. Although not common, lethal trap trees have been used to suppress populations by attracting beetles to insecticide-treated felled trees with the aim of killing the beetles yet little data is available on their effectiveness. In October 2003, a lethal trap tree treatment was implemented in the Routt National Forest in Colorado in an area adjacent to the Steamboat Ski Resort, to minimize population movement into this high-value area. Along with the project, a study was conducted to evaluate treatment effectiveness. Felled trees were divided into two sections; one was sprayed with carbaryl, a common insecticide, while the other one was left unsprayed. In August, 2004, bark samples were extracted from the study trees and from additional completely sprayed trees. We observed no differences in the number of beetle attacks, egg galleries, or life stages between treated and untreated sections of the experimental trees and the completely sprayed trees. Insect populations appeared to be low. We conclude that this technique should not be used until additional data is collected regarding its efficacy.
Negron, Jose F.; Cain, Robert; Cadenhead, Andy; Waugh, Brian. 2019. A test of lethal trap trees for control of spruce beetles. Res. Note RMRS-RN-83. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 9 p.