Increasing resistance of Tetranychus urticae to common acaricides in China and risk assessment to spiromesifen

Abstract

The two-spotted spider mite (Tetranychus urticae Koch) is a widespread, destructive, polyphagous agricultural and horticultural pest. Chemical acaricides are vital for controlling T. urticae, but the mite has developed high resistance to a variety of acaricides in many countries. This study quantifies the resistance to seven acaricides of five field populations of T. urticae collected from roses and vegetables in China and assesses the risk of resistance developing to spiromesifen, which is currently being evaluated for commercialization in this region. Most T. urticae field populations exhibited high resistance to abamectin (154- to 477-fold), etoxazole (158–527), bifenazate (137–239), spirodiclofen (126–263), cyenopyrafen (119–503), and cyflumetofen (140–1360). Notably, all populations had also already developed high resistance to spiromesifen (170–1540). Significant positive correlations were detected between resistance to most of these acaricides, except for spiromesifen. A susceptible population of T. urticae was propagated for 18 generations in the presence of spiromesifen to determine the risk of resistance developing. There was a 9.6-fold increase in resistance. The resistance realized heritability (h2) was 0.1101. Given this degree of heritability and assuming 90% of T. urticae are killed in each generation, a 100-fold increase in resistance to spiromesifen would be expected after only 14 generations. Recent increases in resistance, particularly to cyenopyrafen and cyflumetofen, are also demonstrated. This study illustrates the extent and ongoing development of resistance to acaricides in an economically important pest and demonstrates the importance of evaluating resistance to products that have not yet entered a specific market. Continuous monitoring is necessary to shape resistance management strategies and appropriate choices of acaricide.