June 1, 2007
Invasive Scale Insect Threatens South Florida’s Natural Areas
By Leslie Kimel
At maturity, the lobate lac scale insect resembles a tiny bump of bark. It seems harmless enough, legless and no larger than the head of a pin. But looks can be deceiving—this little critter is one of many invasive pests causing big problems in South Florida’s natural areas.
“Lobate lac scale is an exotic, so it has no natural enemies in Florida to keep it in check,” said Dr. Bill Howard, an entomology professor at the University of Florida. “It is more damaging to its plant hosts than any scale insect I’ve ever seen. Scale insects typically cause branch dieback and chlorosis of the leaves, but the lobate lac scale can actually kill its host plants. Plus, it has a very wide host range.”
Lobate lac scale insects make their living by sucking the sap from woody plants. They congregate in large numbers on small branches and twigs. Adults are completely immobile and spend their lives stuck to their host, protected by a waxy secretion. The tiny red larvae, called crawlers, aren’t so restricted—they have functional legs and are capable of travel. Infestations often spread when crawlers are blown to new spots by the wind.
Lobate lac scale insects damage plants by robbing them of vital fluids. Drained of energy, plants with severe infestations lose branches and can die within a matter of months. Infested plants are often covered in sooty mold, a fungus that thrives on honeydew, the scale’s sweet, sticky waste product. A blanket of sooty mold is unattractive and further weakens plants by cutting off sunlight necessary for photosynthesis.
Native to India and Sri Lanka, lobate lac scale was first discovered in Florida in 1999, in Broward County. Within four years the insect had spread north to Lake Worth, south to Homestead, and west into the Everglades. Experts aren’t sure how the scale arrived in Florida but believe it probably hitched a ride on a live plant. The scale is so small it could easily have escaped detection.
Lobate lac scale has already infested over 300 species of plants in Florida, including many landscape trees, ornamental shrubs, and fruit trees. Commercially important trees like mango, lychee, and star-fruit are vulnerable, but the native wax-myrtle is even more susceptible.
Found throughout the state, fast-growing, evergreen wax-myrtle is an important wildlife tree. In fall, the stems of female plants are lined with tiny blue-green waxy berries that serve as high-energy food for wild turkeys, bobwhite quail, cardinals, white-eyed vireos, ruby-crowned kinglets, palm warblers, yellow-rumped warblers, and many other birds. The foliage is consumed by the larvae of the red-banded hairstreak butterfly.
“Wax-myrtles are a very common native tree in natural areas,” Howard said. “And they’re an important source of food for birds, especially migratory birds. So what we’re concerned about is that by eliminating a lot of wax-myrtles, the lobate lac scale could have an impact on populations of wild birds.”
Due to its waxy protective covering, lobate lac scale is difficult to control with chemical pesticides. However, small trees and shrubs in yards and gardens have been effectively treated with careful applications of horticultural oil, which can smother the insects. For larger ornamental trees, researchers at the University of Florida recommend treatment with products containing the systemic insecticide imidacloprid, including Merit and Bayer Advanced Garden Tree and Shrub Insect Control. Applied as a root drench, the insecticide is absorbed through the roots and spreads through the plant’s vascular system. The insecticide is ingested by the scale as the scale sucks the plant’s fluids.
For very limited outbreaks, chemical treatments may be the answer, but for large infestations in forests and natural areas, researchers believe the best long-term solution is biological control, or use of the scale’s natural enemies. In its native land, lobate lac scale has a whole complex of insects and diseases that help keep it in check. Entomologists at the University of Florida are collaborating with scientists at the Florida Department of Agriculture and Consumer Services and the USDA to research the insect predators that attack lobate lac scale on its home turf. The goal is to eventually introduce one or more of these predators into Florida.
“Because the lobate lac scale is so widespread, biological control offers the best hope for long-term management,” Howard said. But, he added, it will take time for the scale’s natural enemies to be discovered and prepared for release.
Before a biological control agent can be introduced, researchers must be certain it will attack nothing but the target pest. Rigorous studies are conducted in a quarantined environment, and the work is scrutinized by outside scientists from both federal and state agencies. The whole process takes years to complete.
So for now lobate lac scale continues to do its damage, yet another source of trouble for South Florida’s embattled ecosystems.
For more information on lobate lac scale and other exotic pest species, visit www.doacs.state.fl.us/pi/.
