Evaluation of recommended concentrations of eight insecticides for whitefly ( Bemisia tabaci) control in the Republic of Korea

Since its introduction in 1998, Bemisia tabaci has become a major pest affecting greenhouse crops in the Republic of Korea. Insecticidal treatment remains the primary strategy for controlling B. tabaci. The initially introduced B. tabaci populations, identified as the B biotype, were susceptible to neonicotinoids and pyriproxyfen. However, the subsequent dominance of the Q biotype, coupled with the development of insecticide resistance, has necessitated a reassessment of insecticide concentrations. This study evaluated the efficacy of eight commercial insecticides with different modes of action against a laboratory strain (Q biotype) using a leaf-dip assay. The resistance index (RI), defined as the LC90 value divided by the recommended concentration (RC), was employed to assess resistance levels. Four insecticides, pyridaben, milbemectin, spinetoram, and cyantraniliprole, were found to be effective, with RI values below 1. Spiromesifen and sulfoxaflor showed RI values of 1.7 and 5.6, respectively, indicating a need for alternative strategies to ensure effective field control. Notably, the laboratory strain, even after ten years without insecticide exposure, exhibited RI values of 23.8 and 51.3 for thiacloprid and pyriproxyfen, respectively, showing less than 50% control efficacy at 1x RC treatment. These findings underscore the inadequacy of current RCs for commercial products, which were originally established based on bioassays of the B biotype strain. To effectively manage B. tabaci, the RCs of commercial insecticides must be recalibrated based on the susceptible strain of the Q biotype, now the dominant biotype in Korea.