Ball sampling, a novel method to detect Adelges tsugae (Hemiptera: Adelgidae) in hemlock (Pinaceae)

Abstract

AbstractDetection of the exotic hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae), in the crown of eastern hemlock, Tsuga canadensis (Linnaeus) Carrière (Pinaceae), relies mainly on two techniques: (1) sampling of branches from the lower half of the crown using pole pruners; and, (2) visual examinations of accessible foliage from the ground. As a result, infestations starting elsewhere than the lower crown may be missed because the upper crown is out of reach for both techniques. We developed a novel technique called ball sampling, and evaluated its sensitivity at detecting a range of A. tsugae ovisac densities as estimated by pole pruning branch tips of T. canadensis. We launched racquet balls covered with VELCRO® patches of hooks through branches and examined them for the presence of wool produced by A. tsugae. Ball sampling was as effective as pole pruning at detecting infestations in individual trees. If A. tsugae abundance on branches was ⩾0.1 per 10 cm of twig length, as estimated by branch-tip sampling, ball sampling always detected wool in 10 or fewer samples. This technique has the potential to improve detectability of A. tsugae infestations because it can effectively access foliage that is typically inaccessible to other ground-based detection tools.