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Targeting euonymus scale for biocontrol.

Controls reestablish the natural balance, making the mported pest fight for survival.

It's a typical example of what is called classical biological control-introducing natural enemies of accidentally imported pests to help control them. Such controls reestablish the natural balance, making the pest fight for survival.

The latest example of this method may become another successful biological control program for pests of ornamental trees and bushes.

The natural enemies involved are a lady beetle and a smaller beetle, both imported from Asia. Their target pest: euonymus scale, Unaspis euon.ymi, which attacks euonymus plants and also feeds on some other types of ornamental trees and bushes.

"Scale insects fasten themselves to plants with their needlelike mouthparts, literally milking the plant dry of sap," explains John J. Drea, an ARS entomologist at the Insect Biocontrol Laboratory at Beltsville, Maryland. Drea has spent 8 years studying the natural enemies of scale insects. Now his work is paying off.

"Scale pests that attack euonymus plants rank among the most insidious enemies of trees and bushes in the United States," he says. "Many nurseries have stopped selling euonymus because they are so susceptible."

Euonymus rank twelfth among the 20 most common ornamental plants used in the multibillion-dollar landscaping industry. They can be deciduous or evergreen and grown for ground cover, hedges, ornamental vines, shrubs, or trees.

According to Drea, the scale can also infect 30 other types of ornamental plants including pachysandra, hibiscus, and camellia.

"A severe infestation can kill branches and the plant itself-a grave problem in established landscapes," Drea says. In a recent survey of Maryland homes, nearly 70 percent of euonymus had problems due mainly to the scale.

The female euonymus scale is slightly brownish, about 1/16 inch long and shaped like an oyster shell. As many as three generations of this pest can be produced in a year, depending on the climate.

As she grows, the female scale insect forms a hard waxlike armor-the scale-under which she lives and lays her many eggs. Since she has no legs, she never moves again.

In spring, scale eggs hatch and the offspring begin to crawl. About the size of a speck of dust, crawlers have legs and can move about the plant, eventually settling to feed on it.

Male insects form small white scale coverings when they settle to feed on plants. Eventually, tiny white-winged males develop under these covers and emerge as free-living adults that mate with sedentary females. Since adult males have no mouthpans, they cannot feed. They live for about a day.

"The chemicals diazinon, carbaryl, and malathion are often used to control the scale. However, pesticides are effective only for a very short time during the insect's lifecycle. They are unable to penetrate the scale' armor," Drea says. "They also kill off any natural enemies that keep normally innocuous species under control."

Reuniting the natural enemies and scale pest was an epic adventure. "It has taken over 10 years and half a dozen cooperators in ARS and 30 outside the agency to get the biological control program to this stage," he says.

The story began in the early 1980's. Jack Coulson at the ARS National Biological Control Documentation Center in Beltsville included the euonymus scale as a target pest as part of a Small Farms Research Project.

"The project included controlling a group of economically serious scale pests like San Jose, white peach, and prunicola scales whose family includes the euonymus scale," Drea says.

One of Coulson's tasks at the center was to develop a computer program on the movement and use of foreign and native biocontrol agents (insects, mites, nematodes, and pathogens such as fungi, viruses, and bacteria) in the United States. The center keeps track of these agents. The program, called ROBO (Release of Beneficial Organisms), makes this information available to state and academic institutions as well as to federal laboratories.

One of the growing database's many purposes is to provide historical information on natural enemies for introductions made in past decades. Such information helps scientists to re-evaluate these data for current biological control projects.

"Coulson realized over 10 years ago that the euonymus scale had never been a target for biocontrol activities," Drea says.

Since the scale is believed to be oriental in origin and probably came to the United States on nursery stock, Coulson requested the assistance of the ARS Asian Parasite Laboratory at Seoul, South Korea, to obtain natural enemies attacking the scale in Korea. Coulson was at that time the lab's technical adviser.

Entomologist Bob Carlson, now at the ARS Systematic Entomology Laboratory (SEL) in Beltsville, Maryland, was then a foreign explorer in charge of the Korea lab.

Once alerted, scientists there began the long process of examining the literature and museum specimens to uncover clues about the pest's enemies. They began exploring the Korean countryside for scale infestations, collecting its natural enemies for study.

Among these, they found two species of beetles. One was an Asian lady beetle, Chilocorus kuwanae. It is shiny black with a red spot on each wing cover or side. Both sexes look similar and are difficult to differentiate without a microscope.

The other beetle was a 1/25-inch-long nitidulid, Cvbocephalus prob. nipponicus. The female is all black, while males. have dull-yellow heads and black backs.

The two Asian beetles lay their eggs under the body of the euonymus scale and in cracks of the bark or other protected places on the host plant. When larvae hatch, they feed voraciously for about 3 weeks on the scale pest and their offspring.

The lady beetles' powerful jaws enable them to chew through the scale's armor or to dig it out. The smaller beetles destroy the scale by burrowing under its coveting to feed.

In 1982, Carlson shipped several beetles of both types to quarantine officer Larry Ertle at the ARS quarantine facilities at the Beneficial Insects Introduction Research Laboratory in Newark, Delaware. There, the shipment was carefully examined under a microscope to ensure that it contained only beetles.

After rearing one generation of the beneficial insects to eliminate any unwanted parasites, Erfle sent 50 to 100 offspnng of both species to Drea in Bdtsville for additional studies, culture, and release.

The job of officially identifying the two beetles-an essential part of introducing any natural enemy-went to entomologist Robert D. Gordon, who is located at a special SEL unit housed at the Smithsonlan Institution's Museum of Natural History in Washington, D.C. University of Delaware entomologist William A. Connell, now reftreck cooperated in the identification.

In 1983 and 1984, Drea reared and released both species and evaluated them in the United States. Once the colony was established, he sent several dozen beetles back to the Newark lab to former ARS entomologist Robert M. Hendrickson, Jr. He and assistant Sue Barth reared and released the insects there and in the immediate area.

The three then sent one or both types of beetles to more than ,40 cooperators in 24 states in the eastern half of the country, to Washington, D.C., and to national laboratories in New Zealand and Italy. Recipients included state departments of agriculture, botanical gardens, zoos, and private organizations.

One of the first test sites was the U.S. National Arboretum in Washington, D.C. By 1985, this primary release site had become a natural insectary and the main source of both predatory beetles for later shipments to secondary release sites in Maryland, Delaware, Pennsylvania, New Jersey, and Washington, D.C.

From 1984 to the present, some cooperators have set up rearing and distribution programs in their states. Others simply released the beetles. Most have followed up on and monitored the success of the releases.

Field studies in 20 states have shown that the beetles "quickly took hold and all but eliminated the scale from many test plots," Drea says. "In several spots, the beetles decimated the scale population and then disappeared?'

The beneficial beetles returned several years later when the pest reappeared. "Where the beetles went during the interim is not known," he says, "but they came back when they were needed. This is a tremendously positive sign. It's an ideal situation for biological control."

"Some of the people who cooperate with us in testing the beetles are extremely enthusiastic and see a great potential for them," Drea says. "Others ran into problems because homeowners and landscape gardeners removed the sick and dying bushes and the beetles disappeared.

In some areas, ants tending honeydewproducing aphids perceived the beetles as threats to then' food source and interfered with the beetles' establishment."

Because of the overall success of this research, USDA's Animal and Plant Health Inspection Service (APHIS) recently funded a national project for biological control of euonymus scale.

ARS, several universities, and private industry will cooperate in the project that will be coordinated by the APHIS laboratory in Niles, Michigan. It will include several species of tiny wasps and predators that also attack euonymus scale in Asia.

Other pests targeted by APHIS for control with these predators are white peach scale and San Jose scale, the most destructive scale pest of fruit trees.

Last spring, APHIS workers planted 500 plants representing three species of euonymus on a 1-acre site. They plan to deliberately infest the plot with scale to colonize populations of the pest's natural enemies.

"These natural enemies will be massreared, distributed, and evaluated throughout the United States," says Michael D. Bryan, who is with the APHIS National Biological Control Laboratory in Niles, Michigan. APHIS plans to support additional explorations to China to find cold-hardy strains able to withstand the northern U.S. climate.

"If successful, this project will demonstrate the tremendous potential for controlling nursery and ornamental pests using their natural enemies," Drea says. "This field of research for nursery and ornamental pests-has received little, if any, consideration in the past."-By Hank Becket, ARS.

For more information on the biological control project, contact Michael D. Bryan, USDA-APHIS National Biological Control Laboratorv, 2534 South 11th Street, Niles, MI 49120. Phone (616) 683-3563.

Jack Drea has recently retired. He may be reached at (301) 937-8250.
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Author:Becker, Hank
Publication:Agricultural Research
Date:Mar 1, 1992
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