Susceptibility to acaricides in nine strains of the tomato red spider mite Tetranychus evansi (Acari: Tetranychidae)

The tomato red mite, Tetranychus evansi Baker and Pritchard, is a herbivore specialized on solanaceous plants, which has rapidly spread through the world during the last decade. It causes serious damage to a variety of crops in Africa and Europe but has not yet been reported to damage solanaceous crops in Japan. Tetranychus evansi is known to occur in Japan and it has the potential to become a severe pest on solanaceous crops here as well. The present study determined the susceptibility of nine T. evansi strains from various countries to 11 acaricides, because chemicals will be used as the first line of control against a new pest when it starts to cause severe damage to crops. Bifenazate, cyenopyrafen, milbemectin, spirodiclofen and tebufenpyrad showed higher toxicity - as indicated by 50% lethal concentrations (LC50) - for imagocidal action, and chlorfenapyr showed higher LC50 for ovicidal action in almost all T. evansi strains, compared with a susceptible strain of Tetranychus kanzawai Kishida. Still, the LC50 of imagocidal action of all acaricides, and for ovicidal action of all but one (cyflumetofen), on all nine strains tested was much lower than the recommended concentrations. These results suggest that mites from all nine strains could be controlled with acaricides as a first method, should they occur in high numbers on crops.