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Article in Environmental Entomology (PDF
Format, Oct. 2002)
Wasp Eyed as Sunflower Ally
By Jan Suszkiw
November 18, 2002
A tiny wasp that attacks sunflower seed weevils may prove a
useful ally of farmers in protecting their crop's prized seed and oil.
In the journal Environmental Entomology,
Agricultural Research Service scientist
Larry Charlet reports on results of field surveys and studies in which
Triaspis aequoris wasps were the predominant natural enemy of red
sunflower seed weevils. Charlet's survey ran from 1991 to 1995 at 35 field
sites in North Dakota, South Dakota, Minnesota and Nebraska, where the weevil's
larvae are pests of both oilseed and confectionery sunflower crops.
The black, 2.5-millimeter-long wasps don't eat the weevils, but
rather lay their eggs on weevil larvae in the seed of the sunflower's head.
After hatching, the wasp's maggot offspring devour their larval hosts alive.
However, the pest's gruesome demise isn't likely to win sympathy from
commercial growers, who spend $10 to $15 per acre on insecticide spraying.
Charlet, at ARS' Red
River Valley Agricultural Research Center in Fargo, N.D., is studying the
biology, seasonal emergence and other characteristics of T. aequoris to
ascertain its potential as a biocontrol agent. Eventually, the information
could help sunflower growers devise ways to fight the weevil using nonchemical
controls, such as altered planting dates, trap cropping or tillage, that allow
wasp populations to flourish. Another possibility is to release lab-reared
wasps into sunflower fields as they're needed.
T. aequoris wasps are one of 17 "parasitoid" species
known to attack red sunflower seed weevils. Other natural enemies include a
Metarhizium fungus and predatory ants and flies. But none are used
commercially in sunflower, according to Charlet.
T. aequoris is appealing because it probably co-evolved
with the weevil in the United States, is host-specific, and occurs in both wild
and cultivated sunflower. Also, the wasp is adapted to conditions of the
central and northern Great Plains, where much of the nation's 2.5-million-acre
sunflower crop is grown.
ARS is the U.S. Department of
Agriculture's chief scientific research agency.