For many folks, one of the best traditions of the holiday season is the annual visit to the Christmas tree farm to choose and cut an evergreen to enliven the home. Douglas firs are one of my favorites, and a few years ago I was fortunate to find one loaded with a fine collection of white, fluffy egg sacs courtesy of the Cooley spruce gall adelgid. These curious suckers moved to the eastern United States from the Colorado Rocky Mountains along with their host trees, Douglas fir and various species of spruces.
On Douglas fir, female adelgids make white, cottony masses of wax in which dozens of eggs will be laid. From these eggs hatch nymphs that insert tiny beaks into the fir tree where they obtain nutrients and will pass a second generation before migrating to spruce trees, including Colorado blue spruce. After passing the winter on spruce, with the arrival of spring they tap into new shoots with their beaks and secrete potent growth regulators that enslave the developing spring growth and command it to form curious, pineapple shaped galls at the terminals of branches.
From these galls emerge winged migrants that return to Douglas fir to complete their complex and bizarre life cycle. One way to manage these insects in Christmas tree plantations and landscapes is to avoid planting Douglas firs and spruces in close proximity. But for bug geeks, what fun it is to find a beautiful Douglas fir already decorated with adelgids for Christmas!
To celebrate the adelgid and get into the holiday spirit, why not sing a verse or two of the Cooley spruce adelgid song? It’s sung to the tune of Rudolph the Red-Nosed Reindeer. If you forgot the tune, or never knew it, just click on this link and sing along with the Bug Guy.
Cooley spruce gall adelgid
We all know their evils.
But what do I see
All over my Christmas tree?
Cooley spruce gall adelgids
Decorate my fine fir tree,
Lots of white balls of waxes
Full of small bug eggs for me!
Later on in the springtime
When warm breezes start to blow
Hundreds of eggs will have hatched
Into tiny nymphs, you know.
Nymphs will take their small sharp beaks
And jab them in the tree;
Sucking sap is what they do -
Glad they don’t suck me or you!
Then they turn into adults
And develop wings and fly
To Colorado spruce trees
That are growing right nearby.
Our apologies to Gene Autry, who recorded a version of Rudolph the Red-Nosed Reindeer composed by Johnny Marks in 1949. The interesting article “Phylogeography of a specialist insect, Adelges cooleyi (Hemiptera: Adelgidae): historical and contemporary processes shape the distribution of population genetic variation” by Robert G. Ahern, David J. Hawthorne, and Michael J. Raupp was used as a resource for this episode.
To learn more about the Cooley spruce gall adelgid, please visit the following website: