Abstract
We investigated susceptibility to 12 insecticides in populations of the oriental tea tortrix, Homona magnanima Diakonoff, collected from tea fields in Shizuoka Prefecture from 2004 to 2008. In the Shimada- Yui populations, the corrected mortalities 8 days after treatment with each of three insect growth regulator (IGR) insecticides, i.e. tebufenozide, methoxyfenozide, and chromafenozide [diacylhydrazine (DAH) analogs], showed slightly lower mortality compared to the susceptible strain except for chromafenozide. The mortalities to methoxyfenozide showed a gradual decrease in five years. Resistance ratios based on LC50 of tebufenozide were 10.7 and 30.1; those of methoxyfenozide were 10.9 and 11.7 in 2005 and 2006, respectively. In the case of treatment with flufenoxuron and lufenuron [both benzoylurea (BU) analog], the susceptibilities from 2004 to 2008 did not change with a clear tendency, although the susceptibility to flufenoxuron was considerably lower than lufenuron in each year and population, the resistance ratio of flufenoxuron in 2005 was 305.7. Flubendiamide, profenofos, chlorpyrifos, emamectin benzoate, and spinosad showed high insecticidal effects. As for methomyl, its resistance was found in 1980s, the change of methomyl-susceptibility was not clear.
