Adelgids 

- Some don't even look like insects! -

Summary: These small, sap-sucking insects are important pests in forests, landscapes, and Christmas tree plantations. Some are very difficult to control because of a waxy protective covering that they hide under.

Jack DeAngelis, PhD
OSU Ext. Entomologist (ret.)
my resume

What are adelgids?

Adelgids are aphid-like insects in the genus Adelges (family Adelgidae) that feed mainly on conifers. Conifers are trees and shrubs that bear cones such as pine, spruce, hemlock, Douglas-fir, true fir, and many other valuable landscape and forest species. Like aphids, adelgids feed by tapping into their host plants and withdrawing plant sap. Infestations can cause branch dieback, growth deformation and in severe outbreaks even death of the host plant. Entire forests can be killed by certain adelgids such as the hemlock woolly adelgid (see photo right).

Adelgids can be important pests in landscapes, plant nurseries, Christmas tree plantations and forests. Since both aphids and adelgids tend to be somewhat host plant-specific, adelgid identification usually begins with correct identification of the host tree or shrub (see below).

Adelgids usually cover themselves with a waxy coating (right). This wax can make mature adelgids very difficult to control with spray-type insecticides. The best control strategy is to treat the young, unwaxed, stages with an overhead spray such as insecticidal soap then treat waxed stages with a systemic insecticide like imidacloprid (see Merit Insecticide).
hemlock woolly adelgid

hemlock woolly adelgid (Adelges tsugae); the adelgids are covered with white wax

Tree identification

If you know what kind of tree you have use the table below to identify the respective adelgid and aphids pests. If you are unsure of your plant's identification use this tree identification key from Oregon State University. Use the "dichotomous key" link to identify an unknown. Once you know the plant, use the table below to identify the aphids and adelgids that can infest your type of plant.

Control of aphids & adelgids

Healthy trees and shrubs can usually tolerate a fair number of these pests without much damage. Therefore, your first efforts should be to create healthy plants through proper water, fertilizer and soil management.

If populations are high and damaging, unwaxed aphids can be effectively controlled with a strong overhead spray of plain water from the garden hose followed by treatment with insecticidal soap (see Using Insecticidal Soap to Control Aphids). You may need to repeat this several times during the summer because the soap has no residual activity.

Waxy, mature adelgids should be treated with a systemic insecticide like imidacloprid (see above). This insecticide moves around in the plant's vascular system and poisons aphids or adelgids when they feed

How to identify aphids and adelgids on some conifers

The table below can help you identify some of the aphids and adelgids on Douglas-fir, true firs and spruce. Because these insects are somewhat host plant specific it is sometimes possible to base identification on the host plant itself. The table lists only some of the more common aphid and adelgids that can be found on these trees.

Douglas-fir (Pseudotsuga menziesii)

Large, dark colored aphids without waxy covering. Produce large amounts of honeydew which may attract yellowjackets and ants. ===>
conifer aphids (Cinara sp.)

Small, dark "crawlers" on needles in late spring and/or white cottony tufts of wax on needles before bud break or after mid-June. ===>
Cooley spruce gall adelgid (Adelges cooleyi)

True firs (Abies sp.)

Large, dark colored aphids without waxy covering. Produce large amounts of honeydew which may attract yellowjackets and ants. ===>
conifer aphids (Cinara sp.)

Swelling of branch nodes caused by very small, waxy adelgids. Trunk and branches covered with patches of white, waxy material. ===>
balsam woolly adelgid (Adelges piceae)

Twisting of new needle growth. Small greenish yellow or larger bluish gray (stem mother) aphids. Wax and honeydew produced by aphids may mat needles together and attract yellowjackets. ===>
balsam twig aphid (Mindarus abietinus)

Spruce (Picea sp.)

Large, dark colored aphids without waxy covering. Produce large amounts of honeydew which may attract yellowjackets and ants. ===>
conifer aphids (Cinara sp.)

Pineapple-shape galls or cones on branch tips. ===>
Cooley spruce gall adelgid (Adelges cooleyi)

Twisting of new needle growth. Small greenish yellow or larger bluish gray (stem mother) aphids. Wax and honeydew produced by aphids may mat needles together and attract yellowjackets. ===>
balsam twig aphid (Mindarus abietinus)

Older needles shed, especially on lower, shaded portions of tree. Aphids peak in late winter, disappear by summer. Small, green aphids. ===>
spruce aphid (Elatobium abietinum)

References

Conifer root aphid Prociphilus americanus in Oregon (1998) This is an unpublished summary used in a 1998 short course. Note: control suggestions may be outdated in this 1998 paper.

Balsam Woolly Adelgid & Balsam Twig Aphid This is an unpublished handout used in a 1998 short course. Basic life history information. Note: control suggestions may be outdated in this 1998 paper.

Aphid and Adelgid Pests of Conifers in Oregon This is an OSU Extension bulletin that I authored in 1994. This bulletin covers most of the important aphid and adelgid pests of conifers with details about life history, monitoring and control.
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