Texas A&M University, College Station, Texas
March 2009
Giant Bark Aphids (Longistigma caryae)
Cynthia W. Mueller, Galveston County Master Gardener
The insect is about 6 mm. long, gray-colored with rows of dark spots, but seems even larger because of the long legs. Eggs laid in the bark in autumn are yellow at first, then turn black. The life cycle is simple, and populations of insects may stay on their host plant for generations. Because these aphids live all summer long, it is a good idea to try to eradicate these early populations now, if you see any signs of them.
The aphids are also found on basswood, hickory, pecan, sycamore, walnuts, and wax myrtles. Often there are signs of sticky honeydew under the trees, and then dark sooty mold will appear. Cars parked under infested trees may be affected by the rain of honeydew.
Look for foliage discoloration and dieback, with the underside of leaves populated by clusters of dark, large aphids. Masses of the dark eggs may be seen stuck to twigs and bark.
Begin by doing everything you can to promote tree vigor and health. On smaller trees try spraying the aphids off with a strong stream of water, insecticidal soap solution or horticultural oil application. Dr. Merchant suggests that if this does not make a difference, you might use Orthene or an insecticide containing imidacloprid such as Bayer Advance Lawn and Garden Spray. Because aphids are tough to kill, wait a few days to see if dead insects are coming loose from the leaves. If not, turn to the stronger insecticides. Check with your local AgriLife Extension agent for a list of approved products. If you see that aphid predators are beginning to increase in response to the infestation, let them do their work without further spraying.
For further information and images of giant bark aphids, see the following website:
EarthKind uses research-proven techniques to provide maximum gardening and landscape performance while preserving and protecting the environment. For more information on EarthKind Landscape Management Practices see our website: https://earthkind.tamu.edu
Homeowners are often puzzled when they discover masses of brownish insects clustered together on tree trunks in the landscape, not really spinning webs or destroying bark, but - nevertheless - obviously up to something.... These clustering insect masses may be identified as Giant Bark Aphids. Opinions are mixed over whether or not Giant Bark Aphids actually kill oaks - but they can completely destroy entire limbs, especially in smaller sized trees.
Consult this site periodically to download pertinent information about other insect problems ongoing in Texas.
