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Hard-Working Wasps Help Protect Apple Crops

American apple growers in the Northeast can thank a European import for helping them battle the tarnished plant bug, one of the fiercest crop pests in North America. Agricultural Research Service entomologist William H. Day, with the agency's Beneficial Insects Introduction Research Laboratory in Newark, Del., began releasing the parasitic wasp, Peristenus digoneutis, as a biological control for the pest in the late 1970s and early 1980s.

The tarnished plant bug, Lygus lineolaris, is a pest of fruits, vegetables, cotton, crops grown for seed and tree seedlings. It is especially damaging to apples, strawberries and other fruits. Adult tarnished plant bugs puncture the immature fruit to feed on its juices. As the fruit grows, it becomes deformed at the bug's feeding sites. Many apples end up so blemished or misshapen that they can't be sold, or can only be sold at a low price--for cider making, for example.

Tarnished plant bugs often live in alfalfa fields, where they feed and multiply even though they don't attack alfalfa itself. Then, when the alfalfa is cut for hay, large numbers of them fly away and live on other crops.

To counter the tarnish plant bugs in alfalfa, Day established P. digoneutis in northern New Jersey alfalfa fields in 1984. Since then, Day has been monitoring three tarnished plant bug-infested alfalfa fields in northwestern New Jersey. During the past decade, Day has found that the beneficial wasps reduced the plant bugs' numbers by 65 percent in these fields. The parasitic wasp has spread from New Jersey into seven other northeastern states, and into Canada. After the wasp arrived in New Hampshire, tarnish plant bug damage to apples in that state dropped by 63 percent.

The tiny P. digoneutis wasp is harmless to humans, but its females sting young plant bug nymphs and lay tiny eggs in them. About 10 days after the wasp eggs hatch into larvae, the nymphs die. Recent research has shown that half the tarnished plant bugs in strawberries are killed by the parasite, and additional research is under way to learn if fruit damage is reduced.

More information about this research is in the May issue of Agricultural Research magazine.

ARS is the U.S. Department of Agriculture's chief scientific research agency.