Comparative toxicity of acaricides to<i>Tetranychus merganser</i>Boudreaux and<i>Tetranychus kanzawai</i>Kishida (Acari: Tetranychidae)

Abstract

ABSTRACT Laboratory bioassays were conducted to determine the toxicity of different acaricides against two strains of Tetranychus merganser Boudreaux and two strains of Tetranychus kanzawai Kishida by probit analysis. The 50% lethal concentration (LC50) value and resistance ratio of the probit-concentration regression was considered to determine the resistance. A laboratory selected susceptible strain of T. kanzawai (Tk-JN) was used to compare the susceptible levels. Adult females of the T. merganser and T. kanzawai strains have little resistance to most of the acaricides. Adult females of the T. merganser Mexican (Tm-MP) strain were resistant to spiromesifen and the T. merganser Thai (Tm-TC) and T. kanzawai Kanaya (Tk-JT) strains were resistant to spirodiclofen and spiromesifen, because their LC50 values were higher than each of the recommended concentrations. For other chemicals, the LC50 values of all strains were lower than each of the recommended concentrations. Eggs of the Tm-MP strain were particularly resistant to bifenazate, cyflumetofen, and fenbutatin oxide, as their LC50 values were higher than each of the recommended concentrations. Eggs of the Tm-TC strain did not show any resistance to any of the acaricides tested. For etoxazole and spirodiclofen, the LC50 values of the Tk-JT strain were higher than the recommended concentrations. The LC50 values of the susceptible Tk-JN strain to cyflumetofen (388 mg/l) and fenbutatin oxide (>10,000 mg/l) were high compared with the recommended concentrations of each acaricide (200 and 240 mg/l, respectively). All other acaricides were effective against all strains. So, several acaricides (chlorfenapyr/tebufenpyrad, cyenopyrafen/cyflumetofen, etoxazole, hexythiazox, and milbemectin) can be considered as candidates for successful control of T. merganser if it invades Japan and cause damages to crops.