Impact of co-infection of Wheat streak mosaic virus and Triticum mosaic virus on virus transmission rates and wheat curl mite reproduction in the field

 Aceria tosichella Keifer, the wheat curl mite (WCM), transmits Wheat streak mosaic virus (WSMV) and Triticum mosaic virus (TriMV) to wheat. WCMs feeding on WSMV infected wheat have higher reproductive potential than mites feeding on virus free plants (Siriwetwiwat 2006), but mites feeding on TriMV infected plants have their reproductive potential reduced (McMechan 2012). In the Great Plains, WSMV is more prevalent than TriMV, but co-infection is frequently observed, increasing symptom severity.  Previous work has shown that individual WCMs feeding on co-infected wheat have enhanced TriMV transmission and reduced WSMV transmission when compared to mites feeding on single infected plants.  Our objectives were to determine if these differential effects due to co-infection also occur in the field.  Four virus inoculation treatments (mock, WSMV, TriMV and WSMV+TriMV) were arranged in a randomized complete block design with six blocks in both 2012 and 2013. The experiment was carried out by placing mite-infested plants in the middle of small cage-covered plots to allow mites to disperse and spread the viruses. In 2012, WSMV prevalence was lower in co-infected cages than in single infected cages. But TriMV prevalence in both treatments was similar. There was an influx of WSMV viruliferous mites across the plots in 2013, making viral prevalence difficult to interpret, but TriMV incidence increased in the double infected plots. We found that the reproductive potential of WCM feeding on double infected plants are lowered and can be higher than mites feeding on TriMV infected plants. These results help explain the epidemiology of the WCM-virus complex.