A Survey of Five Stem-Feeding Insect Pests of Wheat in the Northern Great Plains
The wheat stem sawfly, Cephas cinctus Norton, the wheat stem maggot, Meromyza americana Fitch, the Hessian fly, Mayetiola destructor (Say), the wheat jointworm, Tetramesa tritici (Fitch), and the wheat strawworm, Tetramesa grandis (Riley), have long been considered wheat pests in the northern Great Plains. This paper reports results of surveys for these pests conducted over 3 yrs in parts of Montana (10 counties), North Dakota (14 counties), South Dakota (1 county), Nebraska (4 counties) and Wyoming (1 county). Fields were randomly selected and a mean of 191 stems were sampled from each field. The percentage of stems infested with each pest was recorded. The percentage of parasitized wheat stem sawfly larvae also was noted. The wheat stem sawfly, wheat stem maggot, and Hessian fly were the most commonly encountered pests, recorded in nearly every county. Wheat stem sawfly density was twice that of wheat stem maggot (7% vs 3.2%) in infested fields. Wheat stem sawfly densities exceeded 10% in 4 counties: Da...
Development and Validation of Molecular Markers Closely Linked to H32 for Resistance to Hessian Fly in Wheat
Hessian fl y [Mayetiola destructor (Say)] is an important insect pest of wheat (Triticum aestivum L.). Host resistance conferred by H genes has been the most effective means to manage Hessian fl y populations. More than 32 H genes have been identifi ed in wheat and its relatives. In a previous study, Hessian fl y-resistance gene H32 was assigned to the chromosomal bin 3DL3–0.81–1.00, which also harbors H26. The objectives of this study were to develop and validate sequence-tagged site (STS) markers closely linked to H32 and to determine the genetic relationship between H26 and H32. In this study, 11 wheat EST-derived STS markers linked to H26 and three new STS markers were added to the linkage map of H32 using the International Triticeae Mapping Initiative (ITMI) population. Two of the STS markers, Xrwgs10 and Xrwgs12, were found to fl ank H32 with a genetic distance of 0.5 cM. Another STS marker Xrwgs11, co-segregated with H32. Molecular markers tightly linked to H32 were validated in 12 bread wheat cultivars and an elite breeding line, demonstrating the effi cacy of these markers for marker-assisted selection. Comparative mapping analysis indicated that H26 and H32 are either different alleles at the same gene locus or two different, but tightly linked H genes. Ongoing efforts to perform fi ne mapping and positional cloning of H26 will resolve the relationship between H26 and H32.
Observations on Hyperparasitism of the Wheat Stem Sawfly Cephus cinctus Nort. (Hymenoptera: Cephidae)
The biology of Bracon cephi (Gah.) (Hymenoptera: Braconidae) was described recently (Nelson and Farstad, 1953). During studies from the Field Crop Insect Laboratory, Lethbridge, on the biology of this important parasit, observations were made on various other hymenopterous parasites associated with the wheat stem sawfly, Cephus cinctus Nort. The parasites discussed herein are Eupelmella vesicularis (Retz.) (Eupelmidae), Eurytoma atripes Gah. (Eurytomidae), and Merisus febriculosus Gir. (Pteromalidae). These three parasites have been noted by Gahan (1933) as parasites of the hessian fly, Phytophaga destructor (Say).