Crapemyrtle Aphid: A Cosmopolitan Pest of a Popular Ornamental Tree

By Caleb Wilson, Ph.D.

Crapemyrtles (Lagerstroemia spp.) are ubiquitous landscape trees throughout much of the southeastern United States, and it is easy to see why. Crapemyrtles produce beautiful white, pink, red, or purple blooms for most of the summer, and their vibrant exfoliating bark creates visual appeal during the winter months when most plants are dormant. Crapemyrtles also thrive in full sun; are relatively tolerant of heat, drought stress, and many diseases; and can establish well in a variety of soil conditions. For all these reasons, crapemyrtles are commonly planted in locations such as backyards, parking lots, and roadsides in the southeastern U.S.

Although crapemyrtles can thrive in urban landscapes, they have a variety of associated insect pests that can impair their aesthetics or health. One such pest is fittingly named the crapemyrtle aphid (Sarucallis kahawaluokalani). Although the aphid was first described in Hawaii in 1907, it is native to southeast Asia, as is the crapemyrtle on which it feeds. In an article published in February in the open-access Journal of Integrated Pest Management that I wrote with Matt Bertone, Ph.D., at North Carolina State University, we summarize the distribution, ecology, and management of the crapemyrtle aphid, with a specific focus on the southern United States.

Crapemyrtle Aphid Distribution and Life Cycle

Although the crapemyrtle tree is native to Asia, it has spread to all other continents (aside from Antarctica) through the ornamental plant trade. Perhaps unsurprisingly, the crapemyrtle aphid distribution also closely tracks that of crapemyrtle. In fact, we found that crapemyrtle aphid has been reported in 35 different countries around the world.

Crapemyrtle aphid adults emerge from eggs when leaves begin to emerge on trees. The first-generation females are asexual and begin producing offspring without mating, and those offspring are also asexual. Nymphs are pale to bright yellow with black, club-tipped hairs on their abdomen. Adults are 1-2 millimeters in length and are yellowish green with pink to red eyes and numerous dark patches on their bodies. All adults have wings except for sexually reproducing females, which are produced near the end of the summer. Once the fall equinox occurs, asexual females begin producing sexually reproducing males and females, which then mate and lay their eggs under sloughing bark or branch crevices. Eggs are the overwintering stage, and in the following spring they will hatch when leaves emerge again.

How Crapemyrtle Aphids Do Their Damage

Crapemyrtle aphids use their piercing-sucking mouthparts to extract plant sap from crapemyrtles leaves. As the aphids feed, they excrete honeydew, which accumulates on tree leaves, branches, and other surfaces below trees such as picnic tables or parked cars. Over time, black sooty mold will grow where honeydew has accumulated. The accumulation of sooty mold on crapemyrtle leaves prevents leaves from absorbing sunlight and can result in a loss of leaves from the canopy of infested trees. Local residents who come outside to find their car covered in sticky honeydew will also be understandably frustrated with the aphids in their trees!

Although crapemyrtle aphids are pests of crapemyrtle, they are also associated with diverse communities of natural enemies (a collective term for insect predators and parasitoids). Syrphid flies (Syrphidae), predatory hemipterans like insidious flower bugs (Orius insidiosus), ants (Formicidae), and lady beetles (Coccinellidae) are all commonly found feeding on aphids in landscape crapemyrtles.

Besides natural enemies, many factors influence the proliferation or suppression of crapemyrtle aphids in crapemyrtle canopies. A recent study found that crapemyrtles surrounded by extensive impervious surface cover (think of trees in parking lots) tend to host more aphids relative to trees surrounded by few impervious surfaces. When crapemyrtles are water stressed—as is often the case for urban trees in compacted soil with little water infiltration—aphids are less likely to be abundant in tree canopies. Finally, species identity and cultivar can influence how susceptible crapemyrtles are to aphids. Hybrid crapemyrtle cultivars such as Lagerstroemia indica x fauriei are most commonly planted in landscapes because these cultivars are more resistant to powdery mildew (a plant disease) than are species of L. indica (another commonly planted crape myrtle species). Unfortunately, hybrid crapemyrtles appear to be more susceptible to aphids than are L. indica crapemyrtles. While crapemyrtle cultivars can vary considerably in their susceptibility to aphids, their resistance to other pests and diseases will also vary.

Crapemyrtle Aphid Management Options

So, how should we manage crapemyrtle aphids? First, it is important to monitor trees for aphid infestation by looking for sooty mold on tree branches or leaves and any dripping honeydew coming from tree canopies. Crapemyrtles thrive in full sun, and trees with warmer canopies tend to host fewer aphids. Therefore, it is important to make sure that crapemyrtles are not planted below other tree species or in shaded locations. Pruning trees on a yearly basis can also remove aphid eggs on tree branches and will result in beautiful blooms the next spring. The pruning practice commonly used for crapemyrtles is called “pollarding,” and I have sometimes heard it referred to as “crape murder” because a large chunk of the outer canopy is removed for this process. However, pollarding does produce beautiful blooms in the summer, so if you can stomach the winter pruning damage, your patience will be well rewarded in the summer.

Because a diverse community of natural enemies will feed on crapemyrtle aphids, landscaping choices that support natural enemy communities may aid in aphid management. Crapemyrtles with complex vegetation cover below them—i.e., lots of shrubs, grasses, flowers, or small trees—tend to host greater natural enemy abundance in their canopies, although such effects have not been linked to greater aphid biological control. Nonetheless, research done on other tree species has found that where there is greater plant diversity there are often fewer pests in trees. If you have a crapemyrtle with nothing growing below it, consider adding in some flowering shrubs. Natural enemies love to feed on the pollen and nectar from flowering shrubs, which might convince them to stick around and feed on aphids in tree canopies. If nothing else, your yard will look a lot prettier!

Because crapemyrtles produce summer-long blooms that attract pollinators, and likely natural enemies too, pesticides should be considered a last resort when managing crapemyrtle aphids. Systemic neonicotinoids are often used to manage sap sucking hemipterans like aphids or scales in landscape trees, and, while these products will work for crapemyrtle aphid, recent research has found that they will become absorbed into the pollen produced by crapemyrtle trees at concentrations toxic to pollinators. Unfortunately, it seems this effect occurs regardless of if trees are treated pre-bloom or post-bloom. In contrast, horticultural oils and insecticidal soaps can effectively reduce aphid densities in crapemyrtle, and they do not have residual off-target effects on natural enemies. Other selective insecticides such as flonicamid, flupyradifurone, and spirotetramat will effectively reduce crapemyrtle aphid densities, but they have reduced off-target effects in comparison to neonicotinoids. Thus, we recommend using horticultural oil and insecticidal soap first, then selective insecticides if oils and soaps don’t work, and finally we only recommend neonicotinoids if nothing else is working and aphid populations are still at damaging levels.

Conclusion

The crapemyrtle aphid is a common pest of crapemyrtles that is likely found wherever crapemyrtles are planted. The good news is that aphids can be managed through cultural and biological control tactics, and there are many insecticide options for management that have limited toxicity on beneficial insects. The pollen produced by crapemyrtle trees is an important resource for pollinators and likely natural enemies as well. Because crapemyrtle aphids are consumed by so many predators, they may be important for supporting natural enemy communities within urban landscapes. For example, a study found that predators that fed on the blackmargined aphid (Monellia caryella) would feed on crapemyrtle aphids during periods of time when blackmargined aphids were less abundant. Although it remains to be tested, crapemyrtle aphids might similarly support predators that feed on other pests in the urban landscape.

Caleb J. Wilson, Ph.D., is an assistant professor in the Department of Entomology at the University of Kentucky. Email: c.wilson@uky.edu.