Susceptibility and Resistance to Diacylhydrazine Analog Insect Growth Regulator Insecticides in the Smaller Tea Tortrix, Adoxophyes honmai Yasuda (Lepidoptera: Tortricidae), Collected in Tea Fields in Shizuoka Prefecture, Japan

Abstract

We investigated susceptibility to 15 insecticides in populations of the smaller tea tortrix, Adoxophyes honmai Yasuda, collected from tea fields in the Makinohara area of Shizuoka Prefecture. In the Shimada-Yui population, the corrected mortality 10 days after treatment with each of three insect growth regulator (IGR) insecticides, tebufenozide, methoxyfenozide, and chromafenozide [diacylhydrazine (DAH) analogs], was lower in 2005 than in 2004. In the case of treatment with lufenuron and flufenoxuron [both benzoylurea (BU) analog IGRs], no clear difference in mortality was observed between 2004 and 2005. In the A. honmai populations examined, seven insecticides-chlorpyrifos, profenofos, chlorfenapyr, methomyl, spinosad, emamectin benzoate, and bifenthrin- showed higher insecticidal effects than the IGRs tested. In addition, the susceptibility of the Shimada-Yui population to DAH and BU IGRs was continuously investigated for 5 years. The LC50 values of the DAH analog tebufenozide showed a rapid annual increase after the start of investigations in 2004, and in 2008 far exceeded the registration dose of 200 ppm. The LC50 values of the DAH analog chromafenozide rose sharply from 2004 to 2005, and in 2005 generally exceeded the registration dose of 50-100 ppm. In contrast, although the LC50 values of the DAH analog methoxyfenozide began to rise after 2004, they still remained below the registration dose of 25-50 ppm in 2008. Increases in the LC50 values of the two BU analog IGRs, lufenuron and flufenoxuron, tended to be smaller compared with those of the three DAH analog IGRs. In the Shimada-Yui population, the resistance ratio of four IGRs-tebufenozide, chromafenozide, methoxyfenozide and lufenuron-showed an exponential upward tendency over the 5 years of the investigation. When resistance ratio values were log transformed, significant positive correlations (p<0.05) were observed between the resistance ratios and elapsed years. The slopes of the regression lines obtained for tebufenozide, methoxyfenozide, lufenuron, were 0.36, 0.17, and 0.14, respectively. Furthermore, on the basis of the slopes of the regression lines, it is estimated that there were 2.3-, 1.5-, and 1.4-fold increases in the resistance of A. honmai to tebufenozide, methoxyfenozide, and lufenuron, respectively.