Estimation of median lethal concentrations (LC₅₀) of the controlling substances against Scirtothrips dorsalis in lotus (Nelumbo nucifera)

Three kinds of controlling substances were evaluated for median lethal concentration (LC₅₀) for S. dorsalis in Nelumbo nucifera. These were the insecticide (imidacloprid), biopesticides (wood vinegar and azadiractin), and a biocontrol agent (Beauveria bassiana). Four experiments of controlling substances were separately conducted in the laboratory using completely randomized design (CRD). Second instar of S. dorsalis was exposed to controlling substances in various concentrations. The experiments were monitored at 24, 48, and 72 h. The results showed that LC₅₀ values of imidacloprid at 24 and 48 h were 0.007 and 0.002 mL L^‑1, which were lower than the other substances followed by wood vinegar (1.698, 1.333 and 0.235 mL L^‑1, at 24, 48 and 72 h, respectively), and azadiractin (1.953, 0.013, and 0.002 mL L^‑1 at 24, 48 and 72 h, respectively). The LC₅₀ values of B. bassiana at 24, 48 and 72 h were 2.70×10¹⁰, 1.77×10⁸, and 6.67×10⁷ conidia L^‑1, respectively. It was determined that insecticide is highly effective at very low concentration. However, biopesticide and biocontrol agent are alternative substances for controlling thrips in N. nucifera. The results provide an alternative approach to deciding upon control measures for thrips in lotus fields.