Occurrence of the Wheat Stem Maggot, Meromyza americana Fitch (Diptera: Chloropidae), in Intermediate Wheatgrass, Thinopyrum intermedium (Host) Barkworth and D. R. Dewey (Poaceae), in Oklahoma1

Abstract

The wheat stem maggot is primarily an economic pest of wheat, Triticum aestivum L.; barley, Hordeum vulgare L.; and cereal rye, Secale cereale L. (Poaceae) (Gilbertson, 1925; Allen and Painter, 1937; Rockwood et al., 1947). The larva of the wheat stem maggot enters the culm above the terminal node and feeds within the culm. Consequently, the developing inflorescence withers and dies and turns white in color. The aborted inflorescences are very noticeable among non-infested inflorescences. In Oklahoma, wheat stem maggot infestations have been reported to occur in seed production fields of bermudagrass, Cynodon dactylon var. dactylon (L.) Pers., and weeping love grass, Eragrostis curvula (Schrad.) Nees (Arnold and Ahring, 1987; Kindler et al., 1989). These were the first reported cases of wheat stem maggot to economically impact important warm-season forage grasses. Kindler et al. (1989) reported the percentage of aborted inflorescence in weeping lovegrass ranged from 3.2 to 22.6%. Intermediate wheatgrass, Thinopyrum intermedium (Host) Barkworth and D.R. Dewey, is an introduced forage grass that is used for pasture and hay for livestock in the Northern Great Plains, the Central and Southern High Plains, and much of the western United States. In the Southern Plains, research has shown that perennial, cool-season forage grasses do not persist through prolonged drought. Gillen and Berg (2005) reported a 95% reduction in stand due to drought where precipitation from September 2001 through May 2002 measured 62% of normal. Seeds from surviving plants from pastures used by Gillen and Berg were harvested in June 2002 and increased at the USDA-ARS Southern Plains Range Research Station, Woodward, Oklahoma. It was anticipated that progeny from these plants would have increased tolerance to drought. In late June 2006, aborted inflorescences of intermediate wheatgrass were found in a seed production block at Woodward. Aborted inflorescences were collected from the plot on 30 June, placed in Erlenmeyer flasks containing about 300 ml of tap water, and caged by placing them in a clear plastic bag with a nylon mesh screen on two sides to determine which insect was responsible (Kindler et al., 1989). Adult flies emerged 15–20 days later and were identified as wheat stem maggot using the keys of Sabrosky (1935) and Fedoseeva (1971). The percentage of aborted inflorescences was determined from randomly sampling 10 quadrats (30 3 30 cm) and ranged from 10 to 28%. Accordingly, the wheat stem maggot was confirmed as a pest of intermediate wheatgrass in Oklahoma which is a new host record. Voucher specimens were deposited at the K. C. Emerson Entomological Museum, Oklahoma State University, Stillwater.