Small-Scale Spatial Distribution of Mountain Pine Beetle Attacks by Parent and Brood Adults in Lodgepole Pine Forests...

The mountain pine beetle, Dendroctonus ponderosae, is a bark beetle that can cause extensive tree mortality of its hosts in western North America. Lodgepole pine, Pinus contorta, is one of its primary and most widely distributed hosts. The insect exhibits a one-year life cycle with a dispersal flight of emerging adults, referred to as brood adults, which attack new trees in the late spring-early summer. The larvae develop through the summer and overwinter. The following spring, development resumes, followed by pupation and emergence of a new generation of brood adults. Every year, a proportion of adults survive the winter, referred to as parent adults, re-emerge and attack new trees prior to brood adult emergence. These contribute little to population dynamics, but it is unknown whether these parent adults contribute to host finding by brood adults by initiating attacks that lead to clustering of attacks by brood adults. We tested this hypothesis by sequentially marking attacked trees from early spring to the fall in 2006, 2008, and 2015 in stands in northern Colorado. The sudden increase in the number of attacks indicates brood adult emergence. We tested for clustering of parent adult- and brood adult-attacked trees and of brood adult-attacked trees around parent adult-attacked trees using Ripley's K-function. We found evidence of clustering of parent adult-attacked trees and brood adult-attacked trees, but there is no evidence of clustering of brood adult-attacked trees around parent adult-attacked trees.