Search For Pest Turns Up Dangerous Cousin, UF Researcher Says

March 24, 1999

GAINESVILLE — An all-points bulletin from University of Florida and state pest-control experts for the feared pink hibiscus mealybug netted a surprise.

Although no pink hibiscus mealybugs turned up in response to news articles about their threat, another dangerous plant pest did, the papaya mealybug.

“It’s a good thing we found the papaya mealybug,” said Marjorie Hoy, an eminent scholar in biological control at UF’s Institute of Food and Agricultural Sciences. “We got a head start in controlling it, thanks to the outstanding cooperation of people across the state.

“This discovery of a pest we didn’t even suspect was here shows how easily alien insect species can cross our leaky borders and wreak havoc on our yards, farms and plant nurseries.”

Twenty-six samples of the new menace have been found, and more are still coming in. They have been discovered on hibiscus, papaya, cassava and a handful of other plants in yards and plant nurseries in Palm Beach, Brevard, Manatee and Hillsborough counties.

The insects feed on the sap of plants it attacks and inject a toxic substance into leaves, stunting the plants’ growth and causing them to become gnarled. “One homeowner said the infestation was so bad that he had to prune all his hibiscus plants to the ground,” Hoy said.

“We’re concerned because this pest has been found on both coasts and could have spread to other locations,” said Avas Hamon, an entomologist in the Division of Plant Industry of the Florida Department of Agriculture and Consumer Services.

The Florida discoveries are the only ones in the continental United States, said Dale Meyerdirk, who heads the U.S. Department of Agriculture’s mealybug control program in Riverdale, Md. “It’s been spreading from Mexico and Central America to the Caribbean.

“Finding it in the states gave impetus to our efforts to find natural enemies that we can use to bring it under control,” he said.

USDA officials are hunting in Mexico and Central America, where the papaya mealybug originates, to see if any tiny wasps target it specifically. The USDA also is growing a papaya mealybug colony in the U.S. Virgin Islands.

“We hope to move quickly to test the effectiveness of any natural enemies we collect in Mexico and Central America on the laboratory colony,” Meyerdirk said. “The testing would lead to controlling it with the natural enemies.”

A similar strategy is combating the pink hibiscus mealybug in the Caribbean, where it has caused tens of millions of dollars in damage to a multitude of plants — including hibiscus, citrus trees, beans and ornamental shrubs, Meyerdirk said.

The USDA has grown colonies of a tiny wasp that keeps the pink hibiscus mealybug in check in Asia, where it originates. Females of this wasp species burrow into the mealybugs and lay their eggs. “When the eggs hatch, the larvae eat the internal organs of the mealybugs and kill them,” Meyerdirk said.

“We’ve gotten a 94 percent reduction in pink hibiscus mealybugs in the year and a half since we introduced the wasps in St. Kitts and more than an 80 percent reduction in only four months in Puerto Rico,” he said.

Florida homeowners and plant nursery operators began sending in samples in July in response to news articles asking for help finding possible infestations of the pink hibiscus mealybug. When samples started arriving, Hoy and Hamon suspected they contained pink hibiscus mealybugs. Both insects produce waxy, cottony egg sacs and deform the leaves of plants.

It was only after Hamon put the tiny insects under 400-power magnification that he was able to distinguish them from the pink hibiscus mealybug.

For now, state officials are encouraging people to fight infestations with a commercially available type of ladybug known as the mealybug destroyer.

“The mealybug destroyers should help, although a specific natural enemy that targets papaya mealybugs would be better,” Hoy said. “People must be careful not to use insecticides because they will kill off the mealybug destroyers.”

Another reason not to use insecticides against the mealybugs is that the chemicals are ineffective because the insects protect themselves with the cottony sacs and bury themselves inside damaged buds and leaves.

Meanwhile, the search for the pink hibiscus mealybug continues.

“We want to keep our guard up because we have the natural enemies to fight it,” Hoy said. “Once it arrives, the sooner we get started with biological control, the better.”