PEST 411
Crapemyrtle bark scale Emerging invasive pest
by Shimat V. Joseph, Department of Entomology, University of Georgia infestation begins when the crawlers settle on the bark. Once they settle, they put out their elongated tube-like mouthpart into the stem, access the phloem vessels, and begin to suck up the plant nutrients. The settled crawlers lose all the appendages as soon as they molt into the second nymphal stage. The nymphs are typically pinkish in color (Fig. 2). During the season, the scale population grows and pretty much covers the entire crapemyrtle bark. They complete a life cycle within 2-3 months; there could be 2-3 generations per year. The nymphs, primarily second instars, are the overwintering stage of this scale pest. Photo: Jim Robbins, Univ. of Ark. CES, Bugwood.org
Fig. 1. Crapemyrtle bark scale infestation on crapemyrtle.
The crapemyrtle bark scale, Acanthococcus
UAC MAGAZINE | FALL 2020
lagerstroemiae (Fig. 1) is an emerging threat to crapemyrtle (Lagerstroemia spp.) in Georgia. As the name indicates, this scale pest attacks the bark of crapemyrtle, the only known scale to do so. This scale, a native to Asia, was first confirmed in Dallas, Texas, in 2004. Since then, this pest has gradually expanded its range to the southeastern states. In Georgia, it was first confirmed in Coweta County in 2014. In 2019, they were found infested in an ornamental nursery in south Georgia. They can potentially spread in zone 6 to 9.
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Biology The crapemyrtle bark scale has three life stages: eggs, nymphs, and adults. Females lay eggs in white or gray felt-like eggsac or ovisac. A female can lay up to 100-300 eggs. Within a week, the eggs hatch and the first instars (earliest nymphal stage) typically referred to as crawlers emerge from the eggsacs. Crawlers have appendages such as legs and antennae and are the only mobile stage of this scale insect. Crawlers prefer the cracks and crevices on the bark, and the
Damage Almost all life stages, from crawlers to gravid females, can activity feed on crapemyrtle and cause serious damage. The infested trees can appear severely stunted, with dieback symptoms on the branches. With a severe infestation, the entire tree can die off. When nymphs and females insert their strawlike, piercing and sucking mouthparts into the phloem, they suck up more sugars than they need, and the excess sugars are excreted as excrements referred to as honeydew. Because this scale insect profusely produces honeydew, sooty mold fungus readily develops on the honeydew, and thus, the infested bark appears black in color (Fig. 3). However, sometimes sooty mold fungus develops on the leaves which may not be caused by crapemyrtle bark scale but instead caused by crapemyrtle aphid. If you find a red liquid (hemolymph) ooze out from the crushed scales especially when you rub the scales attached to the bark with your fingers, it most likely to be crapemyrtle bark scale.
Host range Crapemyrtle is the most preferred host for crapemyrtle bark scale. Other potential hosts are American beautyberry (Callicarpa americana),
