Tebufenozide resistance in the smaller tea tortrix, Adoxophyes honmai (Lepidoptera: Tortricidae): establishment of a molecular diagnostic method based on EcR mutation and its application for field-monitoring

The smaller tea tortrix, Adoxophyes honmai Yasuda (Lepidoptera: Tortricidae), is one of the main insect pests of tea, Camellia sinensis Kuntz, in Japan. Recently, A. honmai has developed a high resistance to diacylhydrazine analog insect growth regulators, such as tebufenozide, in Shizuoka Prefecture. Previously, we identified a point mutation (A415V) in the ecdysone receptor gene (EcR), a candidate factor responsible for tebufenozide resistance. In this study, we have developed a molecular method of diagnosis to detect the EcR A415V mutation by polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP). This method was confirmed to be successfully applicable to larvae reared in the laboratory and adults collected by pheromone traps in the field. The appearance ratio of the resistant allele in the A. honmai populations from various Japanese districts examined by the method revealed a high correlation with the magnitude of tebufenozide resistance. These results verified that the A415V mutation is the principal factor responsible for tebufenozide resistance and the PCR–RFLP method may be used as a reliable and convenient tool for monitoring tebufenozide resistance in the field.