Influence of plant-hardiness zone, shoot length, and crown class on the incidence of gouting by the balsam woolly adelgid on balsam fir

Abstract

AbstractWe collected midcrown branches of balsam fir, Abies balsamea (L.) Mill. (Pinaceae), at six different sites located in five different plant-hardiness zones, along a north–south transect in New Brunswick, Canada, to evaluate the effect of plant-hardiness zone, crown class (overstory versus understory), and shoot length during the previous 10 years on the annual incidence of gouting by the balsam woolly adelgid, Adelges piceae (Ratzeburg) (Homoptera: Adelgidae). Site, crown class, and their interaction, along with the square of shoot length, explained 78% of the variation in gouting. Variations in gouting attributed to plant-hardiness zone were probably primarily due to variation in mean January temperature: at each site, the mean January temperature was positively and closely related to the mean level of gouting. The level of gouting was consistently higher on trees in the understory than on those in the overstory. Shoot length was parabolically related to the proportion of shoots with gout. The parabolic relationship between shoot size and the level of gouting is similar to that previously reported for galling adelgids, and suggests that gouting by A. piceae may be greatest on trees with an intermediate growth rate.