In-field prevalence of resistant grain aphid Sitobion avenae (Fabricius)

A concerning development for Irish agriculture is the detection of partial resistance in the main aphid pest (Sitobion avenae) of cereal crops to the most widely used pyrethroid insecticide compound. The mechanism of this resistance, termed ‘knockdown resistance’ (kdr), affects pyrethroid binding and enables S. avenae to survive insecticide exposure. This partial resistance to insecticide means that S . avenae can continue to inflict feeding damage and transmit barley yellow dwarf virus (BYDV), which may carry a significant yield penalty. The incidence and persistence of resistant S. avenae in the Irish population is currently unknown. To address this knowledge gap, in-field sampling of S. avenae was carried out from 2016 to 2018 in the 11 major cereal-growing counties, and 621 cases of S. avenae were screened. Genotyping was used to screen S. avenae for kdr and to determine the diversity of clones in the resistant and susceptible genotypes, thus testing the hypothesis of resistance in a single dominant super-clone. The data were statistically analysed to determine annual variation in resistance levels. Findings revealed that resistant S. avenae are widespread across Ireland, occurring in all the major cereal-growing counties. Despite an initial high prevalence of resistant S. avenae (54%), matching levels detected in the UK, prevalence in Irish field populations appeared not to be increasing over the duration of this study, suggesting that pyrethroids remain largely effective at managing aphid populations. Resistance was detected in a single dominant SA3 super-clone, which may be explained by the loss of cyclical parthenogenesis as a potential impact of resistance alleles.