Balsam Woolly Adelgid: Hosts and Biology

Balsam woolly adelgid is native to the fir forests of central Europe and was introduced into the United States around 1900. The life cycle of the balsam woolly adelgid consists of the egg, three larval instars, and the adult (see Hain 1988 for a more thorough description). The only life stage capable of movement is the first instar larva (termed the crawler) that, upon locating a suitable feeding site, inserts its stylet into the bark and transforms (without molting) into a nonmobile phase, after which the insect is permanently attached to the host tree. As the female feeds, she secretes a dense woolly covering that ultimately covers the entire insect. The crawler stage does not have wings, and between-tree dispersal is a passive process. The adult female produces as many as 248 eggs. These are oviposited within the woolly mass, which acts to protect all of the life stages except the crawler.

All of the true firs (Abies) that are native to North America show some degree of susceptibility to the balsam woolly adelgid (Mitchell 1966). The susceptibility ranges from slight for noble fir (A. procera) and white fir (A. concolor) to moderate for grand fir (A. grandis), corkbark fir (A. lasiocarpa var. arizonica), and Shasta red fir (A. magnifica var. shastensis) to severe for subalpine fir (A. lasiocarpa), Fraser fir (A. fraseri), balsam fir (A. balsamea), and Pacific silver fir (A. amabilis). The insect is established on susceptible hosts in the Eastern and Western United States where it is responsible for significant levels of mortality in some stands. Prior studies suggest that there may be some connection between host monoterpenes and attack success by balsam woolly adelgid (Arthur and Hain 1987).