Journal of Economic Entomology
Woodpeckers have been recognized for many years as a major factor in the natural reduction of Engelmann spruce beetle populations. A means of assessing their value has been developed. Five classifications of woodpecker feeding based on woodpecker work on 225 trees were studies. An analysis of populations measurements showed a correlation between beetle survival and the woodpecker classification and the intensity of infestation in each tree. A heavy woodpecker classification resulted n very little survival at all intensities of infestation. Survival increased both with an increase in intensity of infestation and a lower woodpecker classification. The average reduction in populations increased progressively from 45 to 98 per cent as the woodpecker classification, which was highly correlated with caged survival, progressed from light to heavy. After woodpecker feeding, numerical survival of beetles was greatest in the moderate classification. The effects of woodpeckers on populations of the Engelmann spruce beetle can be evaluated by classifying woodpecker work and measuring the intensity of beetle infestation in the tree.
Knight, F. (1958). Effects of woodpeckers on populations of the Engelmann spruce beetle. Journal of Economic Entomology, 51(5): 603-607.