Bug of the Day: Tropical Soda Apple Leaf Beetle

Though it sounds like the new craze in carbonated beverages, tropical soda apple is not refreshing or fun.

A prickly shrub from the nightshade family, tropical soda apple is known scientifically as Solanum viarum. It’s native to South America, but has become established in the United States – the plant was first detected in the U.S. in Glades County, Florida, in 1988. Since then, it has spread as far as Arizona and Pennsylvania. Commonly called “the weed from hell,” tropical soda apple grows in dense thickets, stealing resources from native plants and disrupting the habitat of many wildlife species.

Tropical soda apple’s growing habits make it a menace to natural areas and farms, but in Florida, it has the greatest economic impact on cattle ranchers, because it reduces the quantity and quality of grazing lands.

Cattle are reluctant to graze on the plant because its leaves have stiff spines projecting right out of the middle, which could make chewing a painful experience. Shunned by cattle, a small patch of tropical soda apple can expand, unimpeded, into a dense thicket that significantly reduces the amount of grazeable land available. This situation can force a rancher to reduce the number of animals grazed on each acre of land, reducing the operation’s productivity and profitability. It’s expensive to fight tropical soda apple with physical control methods, such as mowing, or chemical control using herbicides. In addition, these are only temporary fixes and must be used on a regular basis to have a lasting effect.

If the disruption of cattle grazing weren’t villainous enough, tropical soda apple also hosts many viruses that can kill crop plants, such as cucumber mosaic virus, potato virus Y, tomato mosaic virus, potato leafroll virus, and tobacco etch virus. Pest insects including the silverleaf whitefly, tomato hornworm, tobacco hornworm, southern green stinkbug, and Colorado potato beetle also use tropical soda apple for refuge.

According to a Florida A&M University study published in 2012, tropical soda apple costs the state’s ranchers anywhere from $6.5 million to $16 million annually. That’s not including money spent by farmers, homeowners and state agencies.

How could this sad state of affairs be made right? In Florida’s time of need, an insect superhero took on the seemingly unbeatable foe and saved the impacted ranchers millions of dollars.

Put less dramatically, after many years of surveying the plant’s native range in South America, searching for its natural enemies, UF/IFAS researchers found what they’d been seeking. In Paraguay, they found the tropical soda apple leaf beetle, known scientifically as Gratiana boliviana.

An adult tropical soda apple beetle is about 6 millimeters long and 4–5 millimeters wide. The beetle is monophagous (see this week’s Bug Word of the Day selections for a definition) and feeds on just one plant, tropical soda apple. Larval and adult beetles eat tropical soda apple leaves and can defoliate a plant to the point where photosynthesis is impaired, weakening the plant, rendering it more susceptible to pathogens and potentially killing it altogether.

After a long period of study to evaluate the tropical soda apple beetle, its behavior, its ability to survive in Florida and its potential to feed on plants other than tropical soda apple, the federal Environmental Protection Agency gave permission for the beetle to be released in Florida. This effort involved property owners, scientists from UF and other entities, UF/IFAS Extension agents and government personnel, who worked together to facilitate the introduction of the tropical soda apple beetle to Florida and raise awareness about tropical soda apple management.

Beginning in 2003, more than a quarter-million tropical soda apple beetles reared by the University of Florida, the Florida Department of Agriculture and Consumer Services and the USDA were released in Florida.

Containers of adult beetles were hand-delivered to ranchers and land managers, who were asked to distribute the beetles on tropical soda apple plants in groups of 10 or 20 beetles per thicket. Once released, the beetles require little or no management. Although the tropical soda apple beetle is unlikely to eradicate the weed completely, it may provide a satisfactory level of control on its own, and it can be supplemented with other methods, if needed.

Thanks to the tropical soda apple beetle’s heroic eating efforts, ranchers in St. Lucie County alone save $850,000 a year in control costs. And, now that the beetle is established in Florida, it will always be on guard. Wherever tropical soda apple threatens, the tropical soda apple beetle will be close behind.

You can read more about the tropical soda apple beetle at this Featured Creatures document from the UF/IFAS Entomology and Nematology Department. http://entnemdept.ufl.edu/creatures/BENEFICIAL/BEETLES/Gratiana_boliviana.htm

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Photo by Peggy Greb, USDA-ARS