The large size, gray color and rows of black docks distinguish giant bark aphid.
The giant bark aphid, Longistigma caryae, is the largest aphid in North America. Despite its large size, I rarely receive reports of this insect because in most years its numbers are so low. This year, however, Extension specialists have already had multiple reports of the aphid. One of the last times I reported on an outbreak of giant bark aphids was 2002, coincidentally (or not), also during a spring that followed a mild winter.
Giant bark aphids are about 6 mm-long (1/4 inch), brownish gray with black spots. Their long legs, which makes them appear even larger, give them a spider-like appearance. Males and some females are winged but egg laying females are wingless. When alive they are often partially covered with a bluish white, waxy secretion. The gray body and rows of black spots along its back helps giant bark aphids blend in well on bark.
Unusually, for an aphid, damage to trees from feeding can be severe. It is not unusual for infestations to cause branch and limb die-back. A tree farm in east Texas this spring reported loss of a number of redbud trees, and Shumard red oaks. In addition, wax myrtle and cedar elm were severely damaged. Pecan, hickory, willow and live oak trees have also been reported as hosts for these aphids.
Where heavy infestations occur, the aphids can literally blanket twigs and branches. When this occurs it is not uncommon to find sticky pools of plant sap under trees. If you find these sap pools or clusters of aphids on your tree, I suggest taking prompt action to remove or kill the infestation.
Another type of giant bark aphid, Tuberolachnus salignus is specific to willow, and is probably shown in this picture taken on an "aussie" willow in Lewisville, TX by Lee McClurg. T. salignus has a bump, or large "conical tubercle" on its back.
On smaller trees, aphids may be controlled with a stiff stream of water from a hose. The safest course for larger trees, may be to spot-treat infested branches and trunks with a spray of imidacloprid, malathion, or acephate (Orthene). Bifenthrin has also been reported to be an effective treatment, suggesting that pyrethroid sprays labeled for trees may be a good choice. Insecticidal soap or horticultural oil sprays are the low-impact choices, and may also be effective, although these sprays will require direct wetting of the aphid to get good control.
Consider sharing your experience with these aphids using the comment box below. If you have an infestation to report, include the name of the tree or shrub affected, along with your city and county. Thanks.
I have a wax myrtle tree infested with these nasty bugs right now. I was online to find out what they were and this is definitely what they are. I have the sap pool on the branch below them as well. I am in Flower Mound, TX (Denton County).
THANK you for this article. It was perfectly timed. We have a tree in our court that was covered in this large unidentifiable bugs. I have done search after search and have kept insisting they looked like Aphids on steriods. Low and behold THEY ARE APHIDS. We are located in Sterling, Virginia and in the last 33 years of living in this area (relocated from Bryan) I have never seen these!!!
We have discovered a Giant Bark Aphid infestation of our prized wax myrtle. We have been observing limb die back for the last year and within the last week I observed honeydew on a car windshield parked under a limb. Didn’t know what the problem was until this afternoon when I found a limb literally covered in aphids. Don’t know if I can get them under control in time to save this 50 year old tree/shrub, but we’re just sick we didn’t find the problem until now.
City of Dallas on the border with Mesquite (near the Dallas Athletic Club) Dallas County
April 29, 2012
I am the tree grower in east texas that lost about one-third of our oklahoma redbuds to these nasty insects. Also several small shumardi red oaks and a couple of young cedar elms, a couple of adult wax myrtles. We have never lost a cedar elm to insects before so if the infestation is stong (the aphids covered the entire trunk for about three feet) take quick action and spray all surrounding trees. The pattern of the mortality was about every third or fourth tree, skipping rows, etc. Not a big spray fan, but Bifen XTS killed the suckers. I have never seen a Giant Bark Aphid before, the honeydew (what a strange name for the tar like substance they leave behind) is almost caustic. I sure hope they move on to somewhere else next year.
I am informed by aphid expert Susan Halbert that there is a second species of large aphid called Tuberolachnus salignus. “They have a huge conical tubercle on their backs. I think you can see the tubercles on some of the bugs in the photo. This species is specific to willow.” She notes that these species have not been well-studied by entomologists.
Bad infestation on oak tree in front yard. Will try low impact method for control, oils and soap. Tree is very large. Richardson, Dallas County, Texas