Know your enemy

The wheat curl mite, Aceria tosichella (Eriophyoidea), is widely distributed worldwide and has a broad host range that includes most cereals and several native and introduced grasses. Unless found in extremely high numbers, wheat curl mites generally cause little direct damage in the field other than the characteristic leaf curling and the occasional trapping of the flag leaf. However, both immature and adult wheat curl mite transmit Wheat Streak Mosaic Virus. 

The majority of eriophyoid species are actually known to be highly host-specific; thus the wide host range exhibited by Aceria tosichella (more than 80 species) has long been regarded as an anomaly. More recent research in Australia showed that there are actually at least two local lineages with overlapping geographical distributions and that only one of them is implicated in Wheat Streak Mosaic Virus transmission. 

Now a group of reasearchers from Poland collected morphologically similar Aceria tosichella populations from only five host plants in a small area of western Poland. They used DNA Barcoding and the nuclear D2 region of 28S rDNA to assess genetic lineages and test if Aceria tosichella really is a single, highly polyphagous species. 

Their study reveals that the wheat curl mite is composed of several discrete genetic lineages with variable host ranges and therefore variable pest potential, indicating not only the likely existence of a cryptic species complex, but also the potential for more genetic and host-range diversity if populations are sampled over a broader area on more of the approximately 80 recorded host plants for this species. Only two lineages in the present study appear to have high pest potential on cereals (one specifically for barley), whereas several others appear to specialize on wild grass species.

There is a lot left to do in order to find out which lineage is harmful and which not. At least we have a good idea on how to do it.