Survival of Hemlock Woolly Adelgid (Homoptera: Adelgidae) at Low Temperatures
Abstract:The hemlock woolly adelgid (Adelges tsugae Annand [Homoptera: Adelgidae]) (HWA), a nonnative insect, is a major threat to New England forest and suburban environments, where one of its hosts, eastern hemlock, Tsuga canadensis (L.) Carrière, is a dominant native tree species. To determine the potential spread of HWA into northern New England, we studied the winter coldhardiness of a northerly population. Sistens were collected at three times during the winter and subjected to temperatures typical of those during winter in the next coldest USDA plant coldhardiness zone. Samples collected in January and February 1996 were subjected to -20, -25, and -30°C; those collected in March to -15, -20, and -25°C; all date-temperature treatments were tested at exposure times of 1, 2, 4, 8, and 24 hr. When all exposure times were combined, the percentage of live adelgids after subzero treatment (adjusted for control mortality at 0°C) declined significantly as temperature decreased. In most cases, fewer HWA were alive after treatment as exposure time increased. Significantly more HWA collected in January were alive after treatment than those collected in February and March. This suggests that HWA coldhardiness declines over this time period. When comparing the percentage of live HWA from February and March for -20 and -25°C, a noticeable decline occurred between the February and March sample dates. Although mortality was as high as 95% in one of the most severe treatments (February collection exposed to -30°C for 24 hr), the fact that complete mortality did not occur suggests that HWA may be able to continue to expand its range into areas with colder winters. For. Sci. 44(3):414-420.
Document Type: Journal Article
Affiliations: Vermont Department of Forests, Parks & Recreation, 103 South Main Street, Building 10 South, Waterbury, VT 05676--Phone: 802-241-3676
Publication date: 1998-08-01
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