Crapemyrtle bark scale (CMBS) is a relatively new insect found principally on crapemyrtles (Lagerstroemia) across the Southeast. Known scientifically as Acanthococcus (=Eriococcus) lagerstroemiae (Kuwana), it is a member of the bark or felt scale family (Hemiptera: Eriococcidae). Native to Asia, CMBS was first noticed in a north Dallas, Texas, suburb in 2004. By 2016, the insect had been reported from eleven states. This exotic scale causes heavy honeydew deposits followed by a disfiguring layer of dark black sooty mold which severely diminishes the landscape value of this important ornamental plant. Although not yet quantified by research, field observations suggest heavy infestations of CMBS reduces the size of panicles, delays flowering, and kills small twigs on crapemyrtle. (Note: several common names are used for Lagerstroemia including: crapemyrtle, crape myrtle, crepemyrtle, and crepe myrtle). Instances of crapemyrtle bark scale causing tree mortality have been extremely rare and could be attributed to causes other than the crapemyrtle bark scale. In Asia CMBS has been reported on plants from 16 genera in 13 families, most notably persimmon and pomegranate. In the US the scale has also been recorded feeding on Callicarpa americana (American beautyberry).
Identification
Crapemyrtle bark scale is easy to identify since, in the U.S., it is the first and only known bark scale to occur on crapemyrtles. The adult females appear as white or gray felt-like encasings on small twigs to large trunks, often appearing near pruning wounds or in branch crotches on older wood. On the most current flush of growth and under heavy infestation, distribution may be more uniform. Up close, CMBS is white to gray in color and approximately 2 mm (0.08 inch, a bit longer than the thickness of a dime) in length. Careful examination may reveal dozens of pink eggs or crawlers under some of the larger white scale covers. Most gardeners will be alerted to CMBS by black sooty mold which appears on the bark. The presence of sooty mold may confuse the diagnosis since that is also commonly associated with a significant aphid or whitefly problem. This felt scale is not classified as either an armored or soft scale.
Life Cycle
As the female nymph matures, it secretes waxy white threads that become felted or matted into a thick whitish to grayish scale covering its entire body. Adult females under this covering are wingless and sessile (attached and unable to move).
The adult female lays eggs under the covering from May to September and then dies. Like other scale insects, the first-instar (first-stage) nymphs have legs and are mobile, thus the term crawlers. These crawlers emerge from under the “mother scale” and disperse within a day or two.
Based on observations from Little Rock, AR (zone 7) in 2014, at least three generations of the scale may occur per year. A suspected fourth generation of the scale has been observed in the Dallas area (zone 8).
It is possible that these scale insects overwinter (spend the winter) as adult females or eggs. In Arkansas, crawlers and later-stage nymphs have overwintered under loose bark and in cracks and crevices.
After the first molt, the nymphs become sessile. The males pupate and develop external wings during the last instar. Because the females do not disperse from the plant, these scales probably spread locally during the crawler stage via wind or birds. Long-distance transport most likely occurs when infested plant material is moved from one city to another.
