Research Article Development of a Dispersal Model for Balsam Woolly Adelgid, Adelges piceae Ratzeburg (Hemiptera: Adelgidae), to Facilitate Landscape-Level Management Planning L. W. Lass, S. P. Cook, B. Shafii, and T. S. Prather Department of Plant, Soil and Entomological Sciences, University of Idaho, Moscow, ID 83844-2339, USA Correspondence should be addressed to L. W. Lass; llass@uidaho.edu Received 30 August 2013; Revised 23 October 2013; Accepted 7 November 2013; Published 5 February 2014 Academic Editor: Scott D. Roberts Copyright © 2014 L. W. Lass et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Te balsam woolly adelgid (Adelges piceae Ratzeburg) attacks subalpine fr (Abies lasiocarpa (Hook.) Nutt.) in eastern Washington, Oregon, and northern Idaho. Historical balsam woolly adelgid distributions present an opportunity to understand climatic factors that infuence the species’ distribution at a landscape scale. Te distribution data allows for creation of predictive models that detail the likelihood of occurrence and associated geographic data allow modeling of species dispersal. Predictive variables linked to the distribution of the hosts and to abiotic environmental conditions were utilized to create a spatial probability model of occurrence. Balsam woolly adelgid predominantly disperses by wind, and hence, both wind speed and wind direction were used to create a dispersal probability model. Results from wind dispersal modeling suggested that two-thirds of the new infestations were due to July and August wind direction and speed. Average July winds ranged from 0.5 to 3.27m/s, fowing south westerly, and August winds ranged from 0.43 to 1.55 m/s, fowing north easterly. Land managers can use the results of the predictive model to better understand where current infestations are likely to expand. Prediction of where the balsam woolly adelgid might move allows managers to adjust actions to respond to future insect movement and establishment. 1. Introduction Invasive species represent a serious threat to the health and productivity of natural systems throughout North America. Balsam woolly adelgid, Adelges piceae (Ratzeburg) (Hemiptera: Adelgidae), an insect native to the fr forests of central Europe, was introduced to the United States around 1900 and is considered a pest of native North American true frs [1]. Te life cycle of balsam woolly adelgid consists of egg, three larval instars, and adult female stages [2]. Te only life stage capable of movement is the frst instar larva (termed the crawler) that, upon locating a suitable feeding site, inserts its stylet into the bark and transforms (without molting) into a neosistens, afer which the insect is permanently attached to the host tree. Te insect secretes a dense waxy covering, once attached, that ultimately covers the entire insect. Te crawler does not have wings and dispersal between trees is a passive process with individuals carried primarily by wind. Te adult female produces up to 250 eggs that are oviposited within the woolly mass which acts to protect all of the life stages except the crawler [2]. Depending upon local conditions and eleva- tion, balsam woolly adelgid populations can have from 2 to 4 generations annually. Two generations per year are common in the mountainous west region of the United States [3]. All native, North American true frs (Abies) show some degree of susceptibility to the balsam woolly adelgid [4]. While grand fr, A. grandis (Douglas × D. Don) Lindley, is pre- sent throughout much of the infested area in Idaho, the adelgid is established on subalpine fr, A. lasiocarpa (Hook.) Nutt., where it is responsible for signifcant levels of mortality [5]. Infestation of frs by the adelgid results in structural changes within the host tissues. Specifcally, the xylem tissue of infested trees has higher concentrations of ray tissue [6, 7], thickened cell walls, and shorter tracheids [8] that have encrusted pit membranes, more closely resembling the pit membranes associated with heartwoods [9]. Tere is a corresponding reduction in water fow in infested trees [6] that stresses the tree and reduces photosynthesis and Hindawi Publishing Corporation International Journal of Forestry Research Volume 2014, Article ID 519010, 8 pages http://dx.doi.org/10.1155/2014/519010