Cooley Spruce Gall Adelgid ( Adelges cooleyi )

*The Cooley spruce gall adelgid, Adelges cooleyi (Gillette), is often incorrectly referred to as an aphid. This close relative of aphids is originally from North America, but is now worldwide in its distribution, wherever its hosts are grown. Aphids have a pair of tubes on the upper tip of the abdomen, while adelgids do not. And adelgids have very short antennae.

The adelgid makes a pine cone shaped gall on Colorado spruce, but lives openly on Douglas-fir needles and branches. It also makes galls occasionally on Englemann and sitka spruces.

The young nymphs feed on tender, expanding needles causing them to twist, curl and discolor. Certain trees seem to react more than others. The summer generation attach to the under surface of fully hardened needles and apparently cause little damage other than forming small waxy balls.

The Cooley spruce gall adelgid has four distinct forms which can be found on Douglas- fir during a season. On Douglas-fir, all the forms inhabit the needles and do not form a gall. On Colorado and other spruces the pest forms a gall at the branch tip.

In nature, the adelgid alternates between spruce and Douglas-fir by undergoing a complex two-year life cycle. However, it can continue for generations on Douglas-fir, year after year, without having to go to Colorado spruce. On Douglas-fir, the adelgid overwinters as an immature female (sistentes) attached to the underside of needles. In the spring, March to mid-April, these small dark brown adelgids begin to suck sap and molt into wingless females covered with long, white, waxy threads. The sistentes lay 10 to 30 eggs in the wax and these eggs produce two types of offspring - winged asexual females (sexuparae) and wingless asexual females (progredientes). Both of these forms move to the new needles, insert their mouthparts for feeding and maturation. The sexuparae fly in search of Colorado blue spruce while the progredientes lay eggs which hatch into new sistentes. By this time, the adults from spruce galls are arriving to produce additional sistentes which overwinter.

The most evident damage caused by this insect is by the first spring generation. Thus, controls generally must be directed towards killing the overwintering sistentes before they lay eggs. Insecticides used for control of this pest must thoroughly cover the needles. Because of this requirement, mist blowers have not been generally effective.

Certain varieties and provenances of Douglas-fir seem to be resistant or tolerant to adelgid attack. Usually the green-colored Douglas-firs are more resistant.

Though this adelgid may discolor the needles, the yellowing tends to disappear by the summer. This will allow for natural predators to build up. However, the spring generation often causes twisting of the needles and this distortion on some trees may not be acceptable.

* Adapted from http://ohioline.osu.edu/hyg-fact/2000/2551.html: Cooley Spruce Gall Adelgid On Douglas-Fir, David J. Shetlar Cooley Spruce Gall Adelgid ( Adelges cooleyi )