DISTRIBUTION OF ATTACKS ON SPRUCE STUMPS BY THE SPRUCE BEETLE, DENDROCTONUS RUFIPENNIS (KIRBY) (COLEOPTERA: SCOLYTIDAE), AND EFFECTS ON THE LENGTH OF EGG GALLERIES

Abstract

AbstractThe distribution of spruce beetle attacks and length of associated egg galleries were investigated on 21 spruce stumps over a 4-year period in central British Columbia. Attack density formed a distinct vertical gradient which peaked near the duff line at about one-third stump height above the mineral soil. The proportion of attacks on the stumps that were located below the duff was linearly related to the ratio of stump height below duff and total stump height above mineral soil. Attack density was significantly higher below the duff than above. A three-parameter exponential function gave satisfactory fit to the attack density gradient on normalized stump height. A discrete-step theoretical model was also developed based on assumptions regarding beetle behavior during landing and imitation of the egg gallery and the physical characteristics of the host. This model gave an excellent fit to the attack density gradient as an average process over all stumps. Average egg gallery length was a curvilinear function of attack density with maximum average egg gallery length occurring at about 0.33 attacks per 100 cm2.