Residue dynamics and bio-efficacy of triflumezopyrim against Nilaparvata lugens and non-targeted effect on natural enemies in a rice ecosystem.

Abstract

Triflumezopyrim (TMP), a mesoionic insecticide, is commonly used for controlling planthoppers in rice. However, the relationship between the TMP residue and toxicity against brown planthoppers (BPHs) has not been studied in detail. We are reporting the dissipation of TMP from rice plant and soil under field conditions. The median lethal dose and median lethal concentration were 0.036ng per insect and 0.525mg L-1, respectively. TMP at recommended dose (25g a.i. ha-1) recorded 1.25 live BPH per hill as against 25.5 per hill in control at 14days after treatment. TMP was considered to be harmless to the natural enemies, namely, Cyrtorhinus lividipennis and Lycosa pseudoannulata in the rice ecosystem. The residue of TMP from rice plant and soil was estimated using the QuEChERS method using three different doses (12.5, 25, and 50g a.i. ha-1). The limit of quantitation (LOQ) of TMP in plant and soil was 5µgkg-1 and 1µgkg-1, respectively. The maximum content of TMP in soil was less than 1% that of plant content on day 1. The dissipation pattern of TMP both from plant and soil was better explained by the first-order double-exponential decay model (FODED) as compared to the first-order kinetic model. Overall, the half-lives of TMP were ranged from 2.21 to 3.02days in plant tissues and 3.78 to 4.79days in soil as per the FODED model. Based on the persistence and toxicity of TMP, we could conclude that TMP will be effective against BPH up to 7-10days after application. Triflumezopyrim with reasonable persistence and high efficacy could be recommended as an alternate pesticide in BPH management in rice.