Acaricide resistance in Norwegian populations of the two-spotted spider mite (Tetranychus urticae Koch) (Acari: Tetranychidae)

Abstract

Farmers and greenhouse crop growers are faced with numerous polyphagus and phytophagus pest species, among which is the two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae). This species has become a deleterious economic pest in many cultivated crops, and its control has posed serious threats to farmers because of its rapid growth rate and speedy adaptation to numerous acaricides. This study is therefore aimed at identifying and characterizing the resistance in two Norwegian populations of the two-spotted spider mite, T. urticae compared to a susceptible strain GSS. Standard bioassay procedures were used to determine the resistance in T. urticae by spray application of different rates of acaricides against the different strains of spider mite larvae. Mortality was scored after 72 hrs. through data collection, analyzed and results expressed in Abbott’s corrected percent mortality and the LC50 values and slopes were estimated by probit analysis, and resistance factor (RF) calculated. The resistance factor (RF) for NOR4 at LC50 for abamectin was twice more than the susceptible strain (GSS). NOR4 showed low levels of resistance to hexythiazox, clofentezin and fenazaquin respectively compared with GSS; it also showed no level of resistance to spirodiclofen and fenpyroximate. Unlike NOR4, NOR5 showed moderate level of resistance to abamectin but with low level of resistance to clofentezine and hexythiazox compared to the GSS strain. But it showed no resistance to spirodiclofen fenpyroximate and fenazaquin. This implies that they exhibited certain level of susceptibility to these drugs.