Monitoring spirodiclofen resistance in female <i>Brevipalpus yothersi</i> (Acari: Tenuipalpidae) from citrus orchards in Southeastern Brazil

Abstract Brevipalpus yothersi Baker is one of the main mite pests in citrus orchards in Southeastern Brazil, causing significant losses in fruit production. Spirodiclofen, an acetyl‐CoA carboxylase inhibitor, is a synthetic acaricide widely used for its control. However, continuous application of a single compound can select for resistant populations. The potential evolution of spirodiclofen resistance in B. yothersi raises concerns about field efficacy and the long‐term sustainability of its use. Monitoring resistance levels across citrus‐growing regions is therefore essential for developing effective management strategies. This study estimated spirodiclofen resistance in 19 field populations of B. yothersi to provide data supporting resistance management programmes. Female mites were exposed to spirodiclofen for 7 days in a direct‐contact bioassay. Toxicity was determined by estimating LC 50 and LC 95 values, and data were spatially analysed in ArcGIS for geographic visualization of resistance ratios. LC 50 values ranged from 1.12 to 236.63 mg L −1 , while LC 95 values ranged from 12.36 to 160,047.00 mg L −1 . Resistance ratios varied from low to very high, reaching up to 80.56‐fold at LC 50 and 12,124.77‐fold at LC 95 among populations. These findings reveal wide variation in spirodiclofen resistance among B. yothersi populations from the Brazilian citrus belt. Such information is critical for guiding resistance management programmes. The rotation of acaricides with different modes of action should be prioritized, particularly in areas with high levels of resistance.