Tiny Wasps Protect High-Value Crops
parasitic wasp, Peristenus,
digoneutis prepares to lay
an egg in a tarnished plant
When John Chapman (a.k.a. Johnny Appleseed) was planting
apple trees in the northeastern United States during the late 18th and
early 19th centuries, he relied on adequate sunlight, moderate rainfall,
and hardy tree stock for his orchards to flourish.
Today, American apple growers in the Northeast still owe
much to rain, sun, and rootstock, but some also benefit from a tiny
parasitic wasp called Peristenus digoneutis.
The wasp, which is native to Europe and harmless to humans, was introduced into the United States in 1979 by William H. Day, an entomologist at ARS' Beneficial Insects Introduction Research Laboratory in Newark, Delaware. Its mission? To battle one of the fiercest pests of crops in North Americathe tarnished plant bug, also known as Lygus lineolaris.
L. lineolaris is a pest of fruits, vegetables, crops grown for seed, tree seedlings, and cotton. It costs farmers billions of dollars every year in control costs and crop losses. In apple trees, for instance, an adult tarnished plant bug will puncture an immature fruit and suck on its sap. As the apple grows, it may become deformed at the bug's feeding site.
Tarnished plant bug,
Day explains, "Many affected apples end up so blemished
or misshapen that they can't be sold or can only be sold at a low pricefor
cidermaking, for example."
Day introduced and established P. digoneutis in
alfalfa fields in northern New Jersey in the late 1970s and early 1980s.
Although tarnished plant bugs don't usually harm alfalfa, they feed
and multiply in alfalfa fields. When the alfalfa's cut for hay, the
bugs fly off and infest other crops.
Since their introduction, the beneficial wasps have helped
control plant bug populations throughout the Northeast. The female wasps
sting young plant bug nymphs and lay tiny eggs in them; about 10 days
after the wasp larvae hatch, they kill the nymphs.
For nearly 20 years, Day has been monitoring three tarnished
plant bug-infested alfalfa fields in northwest New Jersey. He found
that over the past 10 years, the beneficial wasp reduced the plant bug's
numbers by 65 percent in these fields. During the same period, damage
by the tarnished plant bug to apples in New Hampshirewhere the
wasp is also presentwas reduced by 63 percent.
The parasitic wasp can also help fruits other than apples.
Through field sampling, Day and a collaborator have found the wasp parasitizing
30-63 percent of tarnished plant bug nymphs in strawberries.
Day is continuing his monitoring efforts, but he hopes
to interest other researchers in studying the wasp's effects in the
northeastern part of North America. He's stationed in Delaware, but
the wasp is thriving only north of New York City.By Amy
Spillman, formerly with ARS.
This research is part of Crop Protection and Quarantine,
an ARS National Program (#304) described on the World Wide Web at www.nps.ars.usda.gov.
Day is with the USDA-ARS Beneficial
Insects Introduction Research Laboratory, 501 S. Chapel St., Newark,
DE 19713; phone (302) 731-7330, ext. 224, fax (302) 737-6780.
"Tiny Wasps Protect High-Value Crops" was published in the May 2003 issue of Agricultural Research magazine.