Ground and Stem Sampling as Potential Detection Tools for the Wool of Adelges tsugae (Hemiptera: Adelgidae)

Abstract

The wool of the invasive, non-native hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae), occurs mostly on hemlock (Tsuga sp.) twigs, but can be dislodged from the canopy and end up on the forest floor and tree stem underneath the canopy. Herein, we developed and tested the efficacy of two novel sampling techniques, which are based on a visual examination of the forest floor and the hemlock stem for A. tsugae wool. Subsequently, we compared these two techniques to a visual examination of foliage and ball sampling which are two methods currently used operationally. We sampled 11 hemlock stands, with low to moderate incidence A. tsugae populations, near Ithaca, New York in 2016 and assessed the probability of detecting wool on a tree and in a stand, as well as the relative variation and relative net precision for each of the four techniques. We found that sampling the tree stem outperformed foliage and ground sampling, likely because of its higher detection rate and lower relative variation, but not ball sampling. Our findings suggest that combining stem, ball and ground sampling was the most effective combination of techniques and gave a high probability of detecting an infested tree or an infested stand. All techniques were an improvement over foliage sampling, even after increasing the foliage sampling effort fivefold.