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Wooley Ash Aphid

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