Wheat streak mosaic virus (WSMV) (Potyviridae: Tritimovirus) is a major pathogen of wheat (Triticum aestivum) in cropping regions of the Americas, Northern Africa, Asia, and Europe. Cereal varieties such as barley, oats, millet and rye are also susceptible to infection from the virus, although economic impacts are relatively minor in comparison with those observed in the wheat industry. In severe cases wheat may fail to grow, the heads can be sterile and contain no seed, and premature death may occur, causing dramatic reductions in grain yield. In the Great Plains region of North America, WSMV is responsible for average annual yield losses of approximately 5% and complete loss of yield in localised areas. Annual economic losses have amounted to a cost of US$80 million in the state of Kansas alone.

In eastern Australia, isolated cases of WSMV were confirmed in 2003, likely due to a single incursion of infected seed from the Pacific Northwest of the United States. Severe outbreaks in 2005 in the high rainfall cropping region of New South Wales affected at least 5,000 hectares of wheat, with many crops sustaining complete loss of yield. To date, detections of WSMV have been confirmed in all states and territories of Australia, except the Northern Territory, and it is now evident that the entire Australian wheat belt is at risk of WSMV infections. Given the increasing prevalence and spread of WSMV in Australia, there is a need to understand the biology, ecology and genetics of the wheat curl mite (WCM), Aceria tosichella, the vector of this virus.

In addition to wheat, cereal varieties such as barley, oats, millet and cereal rye, and several grass varieties are also susceptible to WSMV infection. Wheat shows the most obvious symptoms of WSMV, and is the preferred host of the WCM (the primary vector of the virus). Maize is also susceptible to WSMV and WCM, however high plains virus (another emerging cereal pathogen in Australia, also vectored by WCM) has much greater impact on maize crop yields. In the USA Sorghum is immune to WSMV and is resistant to WCM colonisation. Other grasses such as brome (Bromus diandrus), setaria (Setaria verticellata), blackgrass (Eragrostis cilianensis), crowsfoot (Eleusine indica), wild oats (Avena fatua and A. sterilis), annual ryegrass (Lolium rigidum), couch (Cynodon dactylon) and phalaris (Phalaris aquatica) are potential reservoirs of WSMV.