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Tiny Ladybug May Help Ease Cotton Insect Woes

Of all the rude things a lady can do, eating her guests tops the list. Offering visitors less than their favorite snacks isn't too sociable, either.

But that's what the Scymnus beetle does to aphids and fire ants. The tiny lady beetles' behavior makes them welcome in cotton farmers' fields.

"It's a good little predator, even though it's very small," said John Ruberson, a University of Georgia research entomologist. "We're working to learn how much insect control the Scymnus provides."

The Scymnus is a type of ladybug. Only about one-third the size of other ladybugs, adults are only an eighth of an inch long. They aren't even big enough to have spots. But they eat caterpillar eggs and aphids that can damage crop plants, particularly cotton.

All ladybugs are beneficial. But at Ruberson's labs on the Tifton campus of the UGA College of Agricultural and Environmental Sciences, he and graduate student Andrea Southworth have found something special about the Scymnus.

During the larval stage, the Scymnus produces a waxy substance from glands on its back. "We're not sure exactly what it does, but the fire ants don't like it," Ruberson said.

The waxy substance protects the ladybug larvae from the ants, allowing ladybugs to multiply quickly in the field.

Fire ants usually kill ladybugs to protect the aphids the ladybugs feast on. Fire ants "farm" aphids for their honeydew, a sweet liquid aphids produce from plant juices.

Ruberson said Scymnus beetles can help farmers, particularly those growing cotton in reduced-tillage fields.

Jimmy Dean, an agronomist with the National Resources Conservation Service, said about 12 percent, or 162,000 acres, of Georgia's 1.44 million acres of cotton is in reduced tillage systems.

Ruberson and Southworth are working to learn the ladybugs' impact in a field.

"As soon as we learn how many eggs and aphids a certain number of the Scymnus eat, we'll be able to find how much insect control they'll provide in a field," he said.

Natural insect control can cut in half the number of sprays farmers use to fight crop-damaging insects.

That can be especially important during dry years. During wetter years, Ruberson said, fungi and diseases help control aphid and caterpillar populations.

Scymnus ladybugs can help indoor farmers, too. "They may be especially helpful in greenhouses where aphids multiply quickly," he said. But they aren't easy to raise for commercial use.

"We know what they like to eat in the field," he said. "But we haven't found a lab diet they like and will thrive on."

Ruberson said they're about three years from making a prediction about how many ladybugs will provide insect control in the field. But recently, he notes, Scymnus populations have increased and expanded across Georgia and as far west as Texas.

"No matter how many are out there," he said, "these numbers can't do anything but help us."

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