Influence of volunteer wheat plant condition on movement of the wheat curl mite, Aceria tosichella, in winter wheat.

The wheat curl mite (WCM), Aceria tosichella Keifer, is the vector of wheat streak mosaic virus and high plains virus which cause significant crop loss in winter wheat throughout the western Great Plains. Volunteer wheat emerging before harvest, as a result of severe hail, is the primary source of mites and virus that infect fall-planted winter wheat. Wind-borne movement of the WCM is of key importance in the spread and infection of the virus complex. Significant movement of WCM from wheat has been thought to be closely tied to the senescence or deterioration of the host. Results from field and greenhouse studies indicated that movement from un-vernalized winter wheat was not closely associated with the deterioration of the wheat host. Greenhouse studies showed no correlation between WCM movement and plant condition, but there was a highly significant relationship between WCM movement and mite population on the host plant. Field studies did not demonstrate increased movement associated with deteriorating un-vernalized winter wheat. However, healthier hosts which were able to support a larger population of mites were associated with increased movement. The main influence on the level of mite movement relates to the size of the source population and not the condition of the host plant, but plant condition appears to be a factor in limiting the increase of the WCM population.