Rapid development of resistance to diamide insecticides in the smaller tea tortrix,Adoxophyes honmai (Lepidoptera: Tortricidae), in the tea fields of Shizuoka Prefecture,Japan

We investigated the susceptibility of the smaller tea tortrix, Adoxophyes honmai Yasuda, to diamide insecticides in the Shimada-Yui tea fields in Shizuoka Prefecture, Japan, from 2006 to 2011. By 2011, the insects had developed significant resistance even to concentrations far above the registration concentrations of two diamides, flubendiamide and chlorantraniliprole. The lethal concentration 50 (LC₅₀) values of flubendiamide showed a rapid annual increase from 16.2 ppm in 2007 to 161 ppm in August 2011, exceeding the registration concentration of 100 ppm in 2010 and 2011. The LC₅₀ values of chlorantraniliprole increased sharply from 25.3 ppm in 2010 to 98.8 ppm in August 2011, exceeding the registration concentration of 50 ppm. The LC₅₀ values for flubendiamide and chlorantraniliprole at 10 days after treatment in insects collected in August 2011 were 105-fold and 77.2-fold higher, respectively, than those in a susceptible strain.