Abstract:
Nonstructural carbohydrates (NSC), starch and sugars, in eastern hemlock infested and not infested with hemlock woolly adelgid (HWA) and elongate hemlock scale (EHS) were analyzed. The use of microwave dried and Wiley milled tissue samples is a superior method for determining NSC content than processing fresh samples of eastern hemlock (roughly 76% higher results than fresh samples). However, the microwave dried and Wiley milled samples should not be stored at room temperature for later enzymatic processing. Spatial patterns studied showed no statistically significant differences in NSC of twigs based on cardinal direction and location in the tree canopy, but there were statistically significantly differences among individual trees within the sample group. Twigs from Tsuga chinensis, a HWA resistant species, had a different NSC content from T. canadensis, with statistically significantly lower sugar and starch contents, when compared after budbreak.
The starch in the needles contributes the highest percentage towards the total NSC, and the starch in the twigs contributes the least. The starch had more variation (year of growth or infestation) than sugar, signifying starch may break down for translocation more frequently than previously thought, serving a multitude of functions besides nutrient storage.
Quantitatively, HWA infestation alters the NSC content of eastern hemlock, in certain tissues of particular ages and at specific times in a season. The greatest statistically significant differences (all higher) in sugars and starch content caused by HWA feeding are found in the previous year’s growth, for sugars in both twigs and
IV needles, and starch in twigs only. However, NSC was affected more by the time (season) of collection and between the years of growth (new growth versus the previous year’s growth) than by HWA infestation. A preliminary test for detecting the presence of a bacteria or virus was undertaken by inserting ground HWA into insect-free seedlings of T. canadensis. After one year, the sample group of inoculated with ground HWA showed no difference in health than another inoculated with deionized water. The NSC of the previous year’s growth needles from EHS infested branches with new growth are not significantly different than without new growth. On the previous year’s growth, EHS infested needles differ from HWA infested needles, with EHS infested needles having statistically significant higher free sugars and lower starch. The EHS infested needles (presumable fed upon by a sugar feeder) had statistically significantly higher sugars, just as the HWA infested twigs (presumable fed upon by a starch feeder) had statistically significantly higher starch.
My data suggests that overall, the changes in NSC content caused by HWA feeding alone does not seem sufficient to be responsible for the decline and mortality of eastern hemlock.
