Crape myrtle, Lagerstroemia indica L., is an exotic ornamental plant introduced to the U.S. from Asia. Its beautiful summer flowers and interesting growth characteristics have made it one of the most popular ornamental plants in the southern U.S (USDA Hardiness Zones 7-10). Horticulturists and homeowners alike love crape myrtle with its summer blooms available in colors of red, pink, white, purple or lavender (Table 1). Crape myrtle grows under a wide range of site and soil conditions. It grows best in full sun but will do well in partial shade. If this were not enough, crape myrtle is easy to propagate and grow, comes in sizes from dwarf shrubs to small trees and has very few insect and disease pests.
Powdery mildew is the only disease of any consequence and resistant cultivars are available. In the upper South and middle Atlantic states, Japanese beetle and an exotic weevil, Callirhopalus bipunctalus, can be pests. A metallic green flea beetle, Altica sp. and a brown striped beetle, Colaspis floridana, are occasional pests.
The crapemyrtle aphid, Tinocallis kahawaluokalani (Kirkaldy), is the most important insect pest in the mid and lower South. Crapemyrtle aphid is host specific to crape myrtle so it does not feed on any other plants. These aphids reach high populations during mid summer. They excrete honeydew copiously as they feed on the plant sap which in turn serves as food for the fungus, sooty mold. Sooty mold colors crape myrtle foliage and wood black, prompting many people to apply insecticidal controls for the aphids. STOP and consider the following before you control the aphids!
Crapemyrtle aphids and their sugar laden honeydew serve as food for twenty to thirty species of beneficial insect predators (good bugs that feed on other bad bugs) (Table 2) and countless bees and wasps. The crape myrtle flowers also attract and provide nectar and pollen to many important pollinating bees. Crape myrtle and its aphids attract these beneficial parasites and predators to crape myrtle and other plants in the surrounding area. The large numbers of aphids encourage the beneficials to remain in the area. Because the aphids are not native to the U.S., most of our native predators do not prefer these aphids over the native species. The predators will leave crape myrtle periodically to search the surrounding vegetation -- your yard and garden -- for their more preferred prey, your other plant pests, thereby, enhancing natural biological control. However, since the crapemyrtle aphids build up to such high populations, the predators usually cannot control them on the crape myrtle (but see below). To enjoy this biological pest control you have to tolerate some crapemyrtle aphids.
Crapemyrtle aphids seem to do better on certain cultivars of crape myrtle plants. Growers may wish to plant small groups of four to eight plants of crape myrtle in strategic growing areas to attract predators. It is of course possible that some predators may be drawn to crape myrtle and away from crop plants, but we believe this potential negative effect is far outweighed by the benefits. Crape myrtle is probably the most important woody landscape plant in the southeastern U.S. for augmenting and sustaining many beneficial insects.
Aphid populations are predictable and peak in most years during July in north Florida and south Georgia (later further north and sooner further south). However, aphids in different locations peak at different times making the aphids much more important for predators over a larger area of landscape. During excessive drought periods crapemyrtle aphids may be the only food available to many beneficial insects. Cultural practices promoting crape myrtle growth such as irrigation, fertilizer and light pruning seem to stimulate aphids and maintain them longer on the plant. Plant some crape myrtles, tolerate the aphids and the sooty mold, enjoy the beauty, and help Nature take its course by enhancing natural biological control of pests.
Post Script: This article was written originally in the late 1980's. In 1993, a new exotic ladybird beetle, Harmonia axyridis, reached Florida as well as colonizing most of the U.S. This ladybird originates from Southeast Asia and prefers to feed on crapemyrtle aphids. As a result crapemyrtle aphids are often eliminated on a localized basis. H. axyridis is the only predator that can completely eliminate crapemyrtle aphids on individual plants. This often has profound effects on the native beneficials. On the other hand, H. axyridis has a very broad host plant and prey range and has become a very important predator of many pests.
Carabidae (ground beetles):
Coccinellidae (lady beetles):
Hemerobeiidae (brown lacewings):
Anthocoridae (minute pirate bugs):
Lygaeidae (seed bugs) and Nabidae (damsel bugs):
Miridae (predatory plant bugs):
Reduviidae (assassin and ambush bugs):
Pentatomidae (predatory stink bugs):
Mizell RF, Schiffhauer DE. 1988. Seasonal abundance of the crapemyrtle aphid, Sarucallis kahawaluokalani (Kirkaldy), in relation to the pecan aphids Monellia caryella (Fitch) and Monelliopsis pecanis (Bissell) and their common predators. Entomophaga 32: 511-20.
Mizell RF, Knox GW. 1993. Susceptibility of crape myrtle, Lagerstroemia indica L., to the crapemyrtle aphid (Homoptera: Aphidiidae) in North Florida. Journal of Entomological Science 28:1-7.
Mizell RF, Fasulo TR, Short DE. (1998). Woodybug: a knowledgebase of pest and beneficial arthropods of Florida woody ornamentals. http://woodypest.ifas.ufl.edu/ (21 November 2003).
Mizell III RF, Bennett FD, Reed DK. (2002). Unsuccessful search for parasites of the crapemyrtle aphid, Tinocallis kahawaluokalani (Homoptera: Aphididae). BioOne. http://www.bioone.org/bioone/?request=get-document&issn=0015-4040&volume=085&issue=03&page=0521 (21 November 2003).
Mizell III RF, Knox GW, Short DE. (1996). Using plant tags to educate consumers about pests/beneficials. IPM Florida. http://ipm.ifas.ufl.edu/ipmfl/v2n3/planttag.htm (21 November 2003).