Spatial distribution of hemlock woolly adelgid (Hemiptera: Adelgidae) ovisacs within eastern hemlock tree: Implications for sampling

Within-tree distribution of an insect pest can help to determine where to sample and apply control measures. This study was conducted to characterize the within-tree distribution pattern of ovisacs and determine sample units suitable for hemlock woolly adelgid, Adelges tsugae (Hemiptera: Adelgidae), on eastern hemlock. A total of 31 eastern hemlock trees infested with A. tsugae were selected from hemlock stands in Blackwater Fall State Park (WV), Cathedral State Park (WV), and Buchannan State Forest (PA). In each tree, 24 branches were selected in six vertical heights and four cardinal directions. The branches were cut and brought to the laboratory to count the number and map the location of ovisacs within each branch. The results of this study showed that A. tsugae ovisacs were more frequently found at the tip of a branch, but no significant differences in A. tsugae density were found among the four directions (F-test, d.f.=1, 3, P > 0.05). This study also showed that 50cm sample from lower branches would be the suitable sample unit for A. tsugae sampling. Implications for sampling of A. tsugae ovisacs are discussed in the presentation.