Mortality Factors in the Life Cycle of Hemlock Woolly Adelgid, Adelges tsugae Annand (Homoptera: Adelgidae) in the Northeastern United States

Populations of hemlock woolly adelgid, Adelges tsugae Annand (Homoptera: Adelgidae), in the northeastern United States are injurious and unregulated, and fluctuate greatly in response to various abiotic and biotic factors. Because the life stages of A. tsugae are sedentary and firmly attached to hemlock twigs throughout most of the year, they are unable to escape the deleterious effects of weather, competitors, and natural enemies. Unusually cold winter temperatures in northern Connecticut in January 2000 following a period of relatively mild temperatures caused major mortality to overwintering sistens nymphs of A. tsugae. Unfrozen and flowing bodies of water near sites and snow cover on lower branches buffered sistens nymphs from cold-temperature-related mortality. Intraspecific competition through negative density-dependent feedback is another important mortality factor on A. tsugae. However, the importance of interspecific competition between A. tsugae and other hemlock pests, such as Fiorinia externa Ferris (Homoptera: Diaspididae) is unknown. Mortality of A. tsugae from native predators is generally inconsistent and low. However, exotic predators, in particular Pseudoscymnus tsugae Sasaji and McClure (Coleoptera: Coccinellidae), are important mortality factors of all life stages of A. tsugae and have good potential for biological control.