Rapid in-field diagnostics to detect pyrethroid resistance in the redlegged earth mite, Halotydeus destructor (Trombidiformes: Penthaleidae) (Tucker)

Pyrethroid resistance in the redlegged earth mite (Halotydeus destructor) continues to be a persistent and expanding problem across the grain belt of Australia, requiring ongoing monitoring to detect emerging local resistance issues. Detection of field resistance in H. destructor currently relies upon the collection and transport of live mites, followed by laborious experiments involving laboratory pesticide bioassays or fairly complex genetic screening assays. Both approaches require trained scientists and are time-consuming and therefore do not provide rapid feedback to farmers. To facilitate the rapid detection of resistance issues, we developed a novel bioassay that can be readily applied in the field using commercially available materials and without the need for training. Although effective in detecting field resistance, this approach was found to be unsuitable in situations where the resistance allele frequency within a mite population was low. To address this limitation, we developed a loop-mediated isothermal amplification (LAMP)-based assay. This approach was successful in distinguishing between homozygote (SS) and heterozygote (RS) mites and, therefore, capable of detecting resistance at low frequency. These tools should help in the ongoing real-time monitoring of resistance in this important agricultural pest.