Selections for fenpyroximate resistance and susceptibility, and inheritance, cross-resistance and stability of fenpyroximate resistance in Tetranychus urticae Koch (Acari: Tetranychidae)

Abstract

Artificial laboratory selections for resistance and susceptibility to fenpyroximate were performed in a population of the two-spotted spider mite, Tetranychus urticae Koch (green-form), collected from a commercial strawberry field in the State of São Paulo, Brazil, in 1999. After five selections for resistance and three selections for susceptibility, the resistance ratios (R/S) at the LC50 and LC95 reached 2,910 and 2,280, respectively. Cross-resistance relationships between fenpyroximate and eight other acaricides were evaluated using the selected susceptible and resistant strains of T. urticae. The results indicate positive cross-resistance between fenpyroximate and acaricides, pyridaben and dimethoate. No cross-resistance was detected for acaricides, propargite, abamectin, milbemectin, fenpropathrin and cyhexatin. The studies on genetics of fenpyroximate resistance indicate that the fenpyroximate resistance is controlled by one major, incompletely dominant factor. Frequencies of fenpyroximate resistance decline significantly in the absence of selection pressure, under laboratory conditions, however, the rate of decline is not high.