Spatial Patterns of Adelges tsugae Annand (Hemiptera: Adelgidae) in Eastern Hemlock Stands: Implications for Sampling and Management

Abstract

Understanding the spatial patterns of insect pests and their associations with their environments is crucial for developing effective sampling and management plans. This study was conducted to identify optimal sampling units for the hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae) and to characterize its spatial distribution patterns in hemlock (Tsuga canadensis (L.) Carrière) stands in West Virginia, USA. To determine the optimal sampling unit, we randomly selected 24 branches from each of 46 A. tsugae-infested hemlock trees. The locations and number of A. tsugae ovisacs on each branch were recorded and the coefficient of variation was used to choose the optimal sampling units. To determine the spatial patterns of A. tsugae, each of the three 1-ha hemlock stands was divided into 100 grids, and ovisac counts were taken from the center of each grid. Semivariograms and spatial analysis by distance indices (SADIE) were used to analyze the spatial patterns of A. tsugae. In addition, various environmental and biological factors were measured to explore their spatial associations with A. tsugae. The results of this study revealed that the A. tsugae ovisacs exhibited spatial aggregation within branches, predominantly at the tips, and a 50 cm branch approximately 3 m above the ground was the optimal sampling unit. The spatial aggregation of A. tsugae in the hemlock stands was evident, and positive spatial associations were found between A. tsugae populations and factors including the aspect, tree diameter at breast height, and tree height. These findings offer valuable insights for the sampling and management of A. tsugae.