Insecticide susceptibility of brown planthopper ( Nilaparvata lugens ) and white‐backed planthopper ( Sogatella furcifera ) in Vietnam and Japan to triflumezopyrim and other insecticides

Abstract BACKGROUND Nilaparvata lugens (Stål) and Sogatella furcifera (Horváth), which are rice planthoppers that migrate from Vietnam to Japan via China, have developed resistance to certain insecticides. Long‐term monitoring of insecticide susceptibility in these insect pests is required to develop effective strategies for controlling their populations. However, long‐term monitoring of the insecticide susceptibility of N. lugens and S. furcifera has not yet been conducted in Vietnam. Here, we determined fluctuations in the median lethal dose (LD 50 ) values of triflumezopyrim, which is a newly developed insecticide, and other insecticides against N. lugens and S. furcifera to reveal the current trends (2018–2024) in the insecticide susceptibility of N. lugens and S. furcifera in Vietnam and Japan. RESULTS The LD 50 values of triflumezopyrim against N. lugens and S. furcifera in Vietnam and Japan remained low during the study period. The LD 50 values of neonicotinoids against N. lugens in both countries exhibited an increasing trend, whereas the LD 50 values of neonicotinoids against S. furcifera remained low. CONCLUSION We clarified species‐specific differences in insecticide susceptibility between N. lugens and S. furcifera . Similar fluctuations in the LD 50 values of the tested insecticides against N. lugens and S. furcifera in Vietnam and Japan supported the hypothesis that Vietnam is the population source of rice planthoppers that migrate to Japan. Overall, our results indicate that at present, triflumezopyrim is effective in controlling rice planthoppers in Vietnam and Japan. However, continued monitoring of insecticide susceptibility is required for insecticide resistance management in East Asia. © 2026 Society of Chemical Industry.