Laboratory-based toxicity of some acaricides to Tetranychus macfarlanei and Tetranychus truncatus (Acari: Tetranychidae)

Abstract

Tetranychus macfarlanei (Tm-BB) Baker & Pritchard and Tetranychus truncatus (Tt-BJ) Ehara (Acari: Tetranychidae) were recently found in Bangladesh as pests in many crops. The susceptibility of eggs of both species to 14 acaricides and of adults to 11 acaricides was examined in the laboratory, using a rotary spray tower. LC₅₀ values in female adults of Tm-BB and Tt-BJ indicated high susceptibility to all acaricides, except chlorfenapyr; LC₅₀ of chlorfenapyr in Tm-BB was approximately 10 times higher than the recommended concentration (492 mg/l vs. 50 mg/l). Ratios of LC₉₀ values and the recommended concentrations (i.e. resistance factor (RF)) indicated 117.07 and 1.16 fold resistance in Tm-BB adults against chlorfenapyr and spirodiclofen, respectively, whereas Tt-BJ appeared to be resistant to tebufenpyrad (RF = 1.65). The RF value of spirodiclofen in Tt-BJ adults was 0.90, suggesting that this should not be used for control of this species, to avoid the further development of resistance. Eggs of both spider mites proved highly susceptible to all the acaricides at the LC₅₀ level. However, RF-ratios based on assays with eggs indicated resistance against chlorfenapyr (1.43) in Tm-BB and fenpyroximate (6.03) in Tt-BJ. RF-ratios of chlorfenapyr (0.87) and milbemectin (0.74) in Tt-BJ eggs suggest these acaricides should be avoided for control of this species. Finally, acequinocyl, bifenazate, clofentezine, cyenopyrafen, cyflumetofen, etoxazole, fenbutatin oxide, hexythiazox and spiromesifen were found to be most effective for control of Tm-BB and Tt-BJ.

Keywords:

• Tetranychus macfarlanei
• Tetranychus truncatus
• acaricide
• susceptibility
• resistance

Acknowledgements

We thank Dr. Y. Kitashima, Ibaraki University, for his kind help in this research. We also thank Mr. M. A. Haque for bringing the mite strains used in this study from Bangladesh to Japan.