College of Agricultural, Human, and Natural Resource Sciences

Department of Entomology

Wooley Ash Aphid

Insects &

Black Widow Spider
Blister Beetle
Box Elder Bug
Cat Face Spider
Cat Flea
Cereal Aphid
Cereal Leaf Beetle
Corn Earworm
Crab Lice
Cooley Spruce Gall Adelgid
False Wire Worm
European Mantis
Jumping Spider
Juniper Scale
Locust Borer
Minute Pirate Bug
Mosquito Diseases
Northern Scorpion
Rose Curculio
Russian Wheat Aphid
Snowball Aphid
Ten Lined June Beetle
Western Yellow Striped Army Worm
Wheat Stem Sawfly
Wire Worm
Wooley Ash Aphid
Yellow Jacket Wasp
Yellow Sac Spider


Wooly ash aphids are the little “gnats” that swarm in the evening this time of year. They can be very annoying to people. They are actually root aphids feeding on fir trees part of the time as you will see below.

Ash trees are considered the primary host for P. americanus, the Wooly Ash Aphid, and noble fir trees, the secondary host. P. americanus is thought to overwinter on ash as eggs placed in bark crevices (Bugwood, 2000). The eggs hatch (eclose) in early spring and produce wingless females which reproduce without mating (parthenogenesis). This aphid form is the fundatrix or stem mother and her progeny are termed fundatrigenia, fundatripuriae, or apterous (wingless) viviparae (live birth) and also reproduce parthenogenetically. The fundatrigenia give birth to winged (alate) aphids called Sexuparae. This winged stage allows the aphid to disperse, generally to the alternate host, the noble fir. This aphid form has both male and egg-laying (oviparae) female offspring. These offspring can mate and are known as “Sexuales”. The female “Sexuales” lay the overwintering eggs on the primary host, ash trees.

No chemical controls are recommended for this aphid.

In the Pacific Northwest, root aphids can be found year round on both noble fir and ash trees according to nursery producers and research in Christmas tree production.

This information is partially from the web page of Dr. Robyn Rosetta, OSU Dept. of Horticulture. The photos contain the name of the photographers. Robyn can be reached at

Department of Entomology, Washington State University, Pullman, WA, 99164-6382 USA, 509-335-5422, Contact Us
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