Beetles at war with invasive weed

U. FLORIDA (US) — A South American beetle drafted into battle is winning the war against tropical soda apple (TSA), an invasive weed that takes over pastures by elbowing out forage grasses ranchers need for their cattle.

The beetle’s success as a biological control agent is reported in the current issue of the journal Florida Entomologist.

Gratiana boliviana, are highly specific feeders whose voracious appetite is focused only on TSA and not on related plants such as eggplant, peppers or potatoes.

TSA “causes a lot of economic problems, and to prevent its spread, you can’t move cattle from Florida to other states without holding them at least six days in a TSA-free area,” says Julio Medal, entomologist at the University of Florida.

“This is enough time to destroy the viability of any TSA seeds that may be in their digestive tracts.”

Nearly 200,000 beetles have been released in the state since 2003, and the insect is now established throughout Central and South Florida, causing invasive weed to suffer significant defoliation as well as decreased fruit, and thus seed production.

TSA can grow taller than 3 feet and equally wide. Its leaves are covered in long spikes, and its immature fruits with pale and dark green stripes resemble small watermelons. It is an aggressive propagator, and cattle will not feed on its leaves.

TSA was discovered in the U.S. more than 20 years now covers more than 1 million acres in Florida and has spread to other states including Georgia, Alabama, Mississippi, and Texas.

Buzz Eaves, a Florida cattle rancher first encountered TSA in 2000 when it began overtaking his forage grasses. After four years of aggressive campaigning against the weed using herbicides, fire and mowing, Eaves allowed IFAS researchers to release the Gratiana boliviana beetles on his ranch.

For the first two years the beetles worked slowly on the TSA and steadily increased in number.

“And then the following year, we had pretty much reached a biological balance with the plants,” Eaves says.

“The TSA plants would start growing in the springtime and be followed a month or two later by the beetles. And the beetles would work on them all summer long, and by the end of the summer, those plants would be skeletonized and away we go to another year.”

The beetles have reduced Eaves’ annual spending on TSA control from as much as $25,000 to nothing.

A South American beetle being used as a biological control agent is having success in the fight against TSA. (U. Florida)

Medal is currently working to gain approval from the U.S. Department of Agriculture for the North Florida release of two more TSA biological control insects. These insects are better adapted to colder climates than Gratiana boliviana, which has failed to establish north of Central Florida.

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