They are out there, billions of them, out of sight, armies of predators and prey, each giving no quarter, each doing what nature intended them to do. They are insects.

And the University of Virginia is using them to keep balance and harmony in nature, deploying predatory insects instead of chemicals to control the pest populations.

“We use an integrated pest management approach at the University of Virginia, which means we use the least hazardous methods to achieve our goals,” said Richard Hopkins, landscape supervisor with Facilities Management.

J. Michael Henrietta, a plant health-care specialist with Facilities Management, said the University first brought in microscopic nematodes to combat white grubs in the soil on the lawn in front of Peabody Hall in 2006. He said the area had been completely torn up by the excavations for the Albert and Shirley Small Special Collections Library’s underground facility between Peabody Hall and Alderman Library.

“They brought in fill and they brought in top soil, and the area was almost sterile,” Henrietta said. “The area was sterilized of natural predators, so we introduced some.”

The grubs had populated the area first and were eating the roots of the grass, and the lawn showed brown patches that indicated white grub infestations. One natural predator for grubs is moles, which tunnel through the soil in pursuit of the grubs, undermining the sod. The mole tunnels are then used by voles, which eat small plant roots. Henrietta instead introduced the nematodes, microscopic worms which get inside the white grubs and kill them from the inside. By introducing the natural predators, Henrietta saved the lawn from several pests.

Because nematodes are so tiny and fragile, they have to be distributed carefully.

“Nematode Heterohabditis bacteriophora is one we use and they come in a slurry in a foam sponge about the size of a kitchen sponge,” Henrietta said. “About 25 million come in a sponge.”

In September 2013, he introduced 5 billion nematodes into the historic Lawn’s 4.7 acres to control a Japanese beetle grub infestation. It took four to five hours to irrigate the Lawn that night after the nematodes were distributed..

“We have a 1,000-gallon sprayer and we squeeze the sponge into the sprayer,” Henrietta said. “We have to spray at dusk, so they don’t dry out and die, and then we have to turn on the sprinklers so that they get down into the soil and not stay on the blades of grass.”

Many of the predators Henrietta uses should be introduced into the environment at night.

“A lot of bugs are attracted to the light, so we have to release them at night,” he said.

While the nematodes are microscopic, they are not the smallest predator in Henrietta’s arsenal. Bacillus thuringiensis, a soil-dwelling bacteria commonly used to combat tent caterpillars and bagworms, is hard to distribute because of its size and fragile nature. He said that microscopic predators do not travel far from where they are distributed. “They may travel a few inches a day,” he said.

Not everything with which Henrietta deals is so small. Lady Beetle larvae, which he uses to control aphids on the Linden trees near the Judge Advocate General School on North Grounds, grow from 1/25 of an inch to 3/8 of an inch.

“The larvae are the most effective,” Henrietta said. “I bought a gallon jug of them and that was cool to see a gallon of beetles.”

He also uses lacewings, which can be ½ to ¾ of an inch, to control aphids on the Linden trees.

Hopkins said introducing predators does not destroy the pests, but can limit the population. “You never get total eradication,” he said.

Henrietta said that insects have cycles, citing a gypsy moth infestation that swelled several years ago to crisis proportions before they died off.

“The population just crashed,” Henrietta said.

Most predators are applied very locally, on specific trees and shrubs, and do not migrate far.

“Constant scouting is needed to discover pest outbreaks early, as these kind of treatments are most effective on early stages of an outbreak of a pest,” Henrietta said. “Many of the people in the landscape department have a trained eye for pest outbreaks.”

Media Contact

Matt Kelly

University News Associate Office of University Communications