Remote Sensing as a Tool to Assess Biological Control of Hemlock Woolly Adelgid

Eastern hemlock (Tsuga canadensis) occupies an important ecological niche in forests of the eastern U.S., including the Great Smoky Mountains National Park (GRSM). A lethal non-native insect, hemlock woolly adelgid (HWA), Adelges tsugae, has caused the death of many hemlocks. A biological control program using releases of a predatory beetle, Sasajiscymnus tsugae, against HWA was initiated in GRSM in 2002. In previous studies, S. tsugae were recovered from 20% of release sites sampled from 2008 to 2012. The objective of this study is to evaluate the effectiveness of remote sensing data on assessing impacts of biological control of HWA to tree health. Normalized difference vegetation index (NDVI) was used to indicate hemlock health in recovery (n=11) and non-recovery (n=51) sites. 20-year remote sensing data from years before and after predator recoveries were used to extract the mean NDVI value of hemlock within a 250m distance of each site. In the years before predator recovery, no significant difference (α=0.05) in NDVI between recovery and non-recovery sites was documented. However, in the years after predator recovery, a significant difference in NDVI between these sites was observed. These results indicate that remote sensing data may have potential to assess biological control of HWA.