Gall Adelgid - Life Cycle

Life Cycle

The life cycle of the gall adelgid requires six generations to complete, only two of which cause damage (nymph stages) and has two migration phases between the spruce and the Douglas-fir. On Douglas-fir, adults are about 0.1 cm long, oval, and light to dark brown in colour. At maturity they are completely covered with white, waxy wool and appear, from spring to fall, as stationary wool tufts on the underside of needles.1

While the chambers of the galls are closed, the nymphs actively feed and increase in size. By midsummer (August to September), the galls begin to dry out, the chambers open and winged forms of the adelgids emerge. These winged adult females have dark red-brown colour, with a heavily sclerotized thorax.3,4 These leave the original tree and most migrate to Douglas-fir trees. The abandoned galls continue to dry out and harden as the plant tissue dies. These dead galls are remnants that are never used again. The gall portion of partial infections dies, while the uninfected segment can continue growth, resulting in curved and convoluted shapes.

On Douglas-fir, eggs are laid on the needles and several generations of woolly adelgids are produced. Yellow spots and bent needles result from feeding damage.2 The needles of light to moderately infested trees exhibit chlorotic mottling where individual adults have fed. Attacked needles may also be twisted. Severely infested foliage may be completely chlorotic and drop prematurely.1 Late in the summer, some of the woolly adelgids develop wings and fly back to spruce to deposit eggs, which produce the overwintering population. Others are wingless and remain on Douglas-Fir trees, where they produce other overwintering forms.2