The eggs and nymphs, which are not attached to the plant via mouthparts are abundant from March through June and can be readily dispersed by wind, birds, deer and other mammals. Humans can also disperse the insect through various activities including moving infested plants. Adelgid feeding and its consequences. The HWA injures susceptible hemlocks by sucking sap and probably also by injecting a toxic saliva while feeding. This causes the needles on infested branches to desiccate, turn a grayish-green color, and then drop from the tree usually within a few months.
Most buds are also killed, so little new growth is produced on infested branches.
Dieback of major limbs usually occurs within two years and progresses from the bottom of the tree upwards, even though the infestation may be evenly distributed throughout the tree. Trees often die within four years, but some survive longer in a severely weakened condition with only sparse foliage at the very top of the crown. These weakened trees are unsightly and have little chance for recovery, often falling victim to secondary pests. Patterns of infestation. An infestation can start anywhere on a given tree depending upon where eggs or crawlers were deposited by the dispersal agent.