Multiple acaricide resistance and underlying mechanisms in Tetranychus urticae on hops

The polyphagous pest Tetranychus urticae feeds on over 1100 plant species including highly valued economic crops such as hops (Humulus lupulus). In the key hop production region of the Pacific Northwest of the USA, T. urticae is one of the major arthropod pests. Over the years, T. urticae control has been dominated by the application of various acaricides. However, T. urticae quickly adapts to these acaricides by developing resistance. Here, we determined resistance ratios of T. urticae populations in hops to three acaricides: etoxazole, fenpyroximate, and spirodiclofen. The mechanisms underlying resistance to these and three other acaricides were investigated in 37 field-collected T. urticae populations using a comprehensive diagnostic approach. Our data showed that T. urticae populations exhibited complex adaptation patterns to acaricides. Resistance to abamectin, fenpyroximate, and spirodiclofen by enhanced target metabolic detoxification gene(s) was identified in 100%, 50%, and 20% of populations tested, respectively. Resistance to bifenthrin, bifenazate, and etoxazole by target site insensitivity was pervasive among tested populations. Our study provides new information in understanding the complexity of T. urticae adaptation to multiple acaricides, which will help in designing sustainable pest control strategies for T. urticae on hops and other economically valuable crops.