Learnings from over a decade of increasing pesticide resistance in the redlegged earth mite, Halotydeus destructor (Tucker)

Abstract

BACKGROUND The redlegged earth mite, Halotydeus destructor (Tucker), is a destructive and economically important pest of winter grain crops and pastures in Australia. It is largely controlled by pesticides, but this mite has evolved resistance to pyrethroid and organophosphate chemicals. A national Resistance Management Strategy has been developed for pro‐active management to delay further resistance evolution, though its success is reliant on a detailed understanding of the incidence, patterns of spread, current distribution and the nature of resistance in the field. Here, we report on a long‐term resistance surveillance programme undertaken between 2006 and 2019 informed by resistance risk forecasting. RESULTS By mapping the Australian distribution of resistance through time, we show that resistance is present across three Australian states and covers more than 3000 km. This current range includes a recently identified population exhibiting organophosphate resistance representing the most easterly location of resistance in H. destructor. Using field history information, we identify associations for the first time between crop management practices employed by farmers and the presence of pyrethroid resistance. Management strategies that could minimize the risk of further resistance include limiting local spread of resistance through farm hygiene practices, crop rotations and reducing pesticide usage. CONCLUSION This study highlights the challenges of resistance in H. destructor but also indicates how quantitative resistance risk analysis can be developed to target field surveillance and delay further resistance. The management strategies highlighted in this study can help maintain the effectiveness of control options but will depend on farmer engagement and adoption. © 2021 Society of Chemical Industry.

Strip spraying delays pyrethroid resistance in the redlegged earth mite, Halotydeus destructor: a novel refuge strategy

“…To ensure the ongoing success of a refuge‐based management approach, resistance monitoring is required (even after the resistant phenotype appears to have been lost from a population). A regional approach to resistance management, where cases of local resistance cases are reported and managed would further improve management outcomes, particularly with distance to existing resistant populations known to be an important risk factor in the evolution of resistance 22 . However, careful consideration of the incentives available to farmers to encourage reporting will be required, as the costs of reporting may be perceived as high when onerous quarantine restrictions are required (as currently occurs in other areas of farm biosecurity).…”

“…The resistance status of RLEM populations across Australia was determined through previous resistance surveillance activities 22 . Resistant populations are defined as RLEM populations that are known to carry the kdr mutation at significant levels (over 5% of alleles), or that have demonstrated a resistant phenotype through pyrethroid dose–response bioassays 9 .…”

“…A pesticide susceptible population from South Morang, Victoria (−37.622929, 145.098979), collected from pasture dominated by legumes with no known history of pesticide usage or resistance, was also included. This population has been confirmed as susceptible through other resistance studies 22 . Briefly, a petrol blower vacuum (Stihl® SH56C) with a metal filter fitted to the intake was used to collect mites by directing the vacuum towards the soil and vegetation.…”

“…To assess the resistant allele frequencies in each of the 63 samples taken from the field trial between 2018 and 2019, we undertook digital PCR, 22 which is a high‐throughput technique. DNA was extracted from pooled mite samples (usually 50 mites, but fewer when mite densities were low) using a Qiagen DNeasy® Blood & Tissue Kit.…”

The mitogenome of Halotydeus destructor (Tucker) and its relationships with other trombidiform mites as inferred from nucleotide sequences and gene arrangements

“…Since its establishment, this mite has been mostly controlled using pesticide, with a long history of organophosphate and pyrethroid chemical usage (Ridsdill‐Smith et al., 2008 ). However, pyrethroid resistance has evolved and become widespread (Arthur et al., 2021 ; Edwards et al., 2018 ; Yang et al., 2020 ), and more recently, geographically isolated cases of organophosphate resistance have been identified (Arthur et al., 2021 ; Umina et al., 2017 ).…”