Hemlock Woolly Adelgid Life Cycle  by Donald Miller  The hemlock
woolly adelgid (Adelges tsugae) is a small insect with piercing
and sucking mouthparts. It is native to Japan but introduced
into the United States where it is an invasive pest. This insect
can attack all species of hemlock (Tsuga spp.) in North America.
Eastern species of hemlock are more susceptible to damage than
are the western. There are two generations of hemlock woolly
adelgid each year. Hemlocks are hardy within U.S. Department of
Agriculture plant hardiness zones 4a through 7b.   In the
spring, adult hemlock wooly adelgids produce a woolly or cottony
sac on the hemlock’s twigs and lay eggs there. Each adult female
can lay up to 100 eggs or more. Early in the summer, a second
generation of adult females lays its eggs, though generally
fewer, in the same manner. Each of the egg stages only lasts a
matter of days or weeks before hatching and giving rise to the
next stage -- the crawlers.   Later in the spring, nymphs emerge
from eggs that