Developing Artificial Rearing Techniques for Hemlock Woolly Adelgid, Adelges tsugae and Balsam Woolly Adelgid, Adelges piceae; Artificial Infestation and Epicuticular Wax Study of Carolina Hemlock, Tsuga caroliniana, Provenances.

Abstract

Adelges tsugae Annand, the hemlock woolly adelgid (HWA), is an exotic pest of hemlocks that is a threat to the health and sustainability of hemlocks in the eastern United States. Hemlocks (Tsuga spp.) are one of the most important ecological, economic and aesthetic tree species of the eastern US. In order to save hemlocks an intensive research effort on HWA is underway. The objective of this study was to develop an artificial diet for HWA and to determine, if there are differences in adelgid infestation rates and fecundity among eight provenances of Carolina hemlock. Sixteen diets were prepared and were tested in liquid, solid and cellular forms to determine their suitability for adelgid development. In addition, feeding and delivery systems were developed to provide fresh diet continuously. All the liquid based diets showed no significant differences and no diet uptake except the MDB-1 and MDB-3 diets. BWA crawlers were able to survive for two weeks on these two diets. The 1st instars survived for 10-12 days on these diets whereas their survival was not more than 3-4 days on other diets. Solid based diets did not show any encouraging results and all the crawlers stopped their activity in 3-4 days on these diets. Digestive track dissection of the HWA suggested the cellular nature of their diet and subsequent cellular based diets allowed 10-15% of the crawlers to develop to 2nd instars, and the2nd instar survival was also high. Amylase tests on the HWA saliva showed very week amylase activity probably from the presence of microorganisms in HWA gut. Variation among Carolina hemlock was observed with respect to infestation rate and fecundity. The infestation level (number of eggs/woolly mass) for the provenances from Caeser head Campground and Crabtree was significantly higher than Wildcat and Table rock, and no infestation was seen in Bluff Mountain, Linville and Cradle provenances. Insects respond to many chemical cues for feeding that can be responsible for susceptibility and resistance of the host. The epicuticular wax was analyzed by GC/MS and linked to the host preference of HWA. Hexacosanol was observed in all the provenances, however the concentration of hexacosanol with other chemicals seems to be dependent on insect infestation. Some other chemicals are also found, which are either deterrents or stimulants in other insects but their role in HWA and hemlock species is not known.