Abstract: Acaricide resistance development in spider mites has been a serious problem instrawberry greenhouses in Japan. IPM strategy may be a relevant measure against the resistantpopulation. Hereby, biological control using phytoseiid mites is spreading to farmers, and alsonew physical control technologies such as UVB irradiation and physical control agents havebeen developed. Now, to evaluate the effects of such alternative control methods delaying thedevelopment of acaricide resistance, a convenient method to measure the frequency ofresistance gene is desired. We have developed a monitoring method for etoxazole resistancegene frequency with a combination of restriction endonuclease digestion and quantification byreal-time PCR (RED-ΔΔCt method). In this talk, we will introduce examples monitoring thefluctuation of etoxazole resistance gene frequency by the RED-ΔΔCt method in the two-spottedspider mite Tetranychus urticae Koch under various spider mite management strategies(chemical, physical, and biological control) in strawberry greenhouse. Mode of inheritance ofetoxazole resistance is completely recessive in T. urticae, so that resistance gene frequency islikely greater than survival ratio in toxicological tests for females though those parameters areequivalent in males. Our results show a drastic increase of resistance gene frequency byspraying with etoxazole while not under physical and biological control.