Analysis of grain aphid (Sitobion avenae) populations- genetic composition and the frequency of pyrethroid resistance

Overall, the frequency of S. avenae carrying kdr-SR collected in the English suction traps was similar in 2012 and 2013 suggesting that this form of resistance may have stabilised. The frequency of kdr-SR varied between English sites in 2013 from 0% (at Starcross) to a maximum of just over 50% (Kirton). Kirton consistently showed the highest kdr-SR frequency which may reflect a higher pyrethroid selection pressure in that area.

The kdr-SR frequency in Scottish S. avenae was overall lower than in the English population with 8% and 27% in the Edinburgh and Dundee traps, respectively, in 2013. No kdr-SR aphids were recorded from the Elgin and Ayr traps in 2013.

A subset of the S. avenae samples tested for the presence of the kdr mutation was also tested to understand their genetic make-up. If a genotype appears more than once during the analysis, this is considered as evidence of a clone (resulting from asexual reproduction). If a particular genotype appears to be unique then this suggests that the individual aphid has arisen from sexual reproduction.

So far, all of the S. avenae shown to have the kdr mutation (and therefore reduced sensitivity to pyrethroids) belong to a single genotype or clone. In addition to this clone, there were also at least seven other clones detected. These are all sensitive to pyrethroids (i.e. do not possess the kdr mutation). There were also many individual S. avenae that were a unique genotype.

England and Scotland differ in the proportion of the population that is clonal. In the areas of England sampled ~75% of the population was from one clone or another, whereas in Scotland, only ~10% was derived from a clone (see below). This is consistent with the hypothesis that the prevalence of individuals which have been derived from sexual reproduction increases at more northerly locations, where the conditions favour the sexual cycle.

Potato Council (PCL) is funding continuation of the survey of the frequency of the kdr-SR genotype and analysis of the genetic diversity of S. avenae populations in 2014. This will provide further information to determine if/how the S.avenaepopulations and frequency of the kdr mutation vary over time and across regions.