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Article in Environmental Entomology (PDF Format, Oct. 2002)

Wasp Eyed as Sunflower Ally

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.