2.2. Bioassay to Determine Insecticide Concentrations for Treatment

A bioassay to identify the LC₁₀-LC₉₀ (resulting in 10% - 25% mortality) for each insecticide was carried out using third instar nymphs according to a previously reported rice stem dipping method [31,32]. Thiamethoxam, abamectin, and cyantraniliprole were dissolved in acetone and diluted to the required concentrations with 0.1% Triton X-100, respectively, and 0.1% Triton X-100 was also used as a blank control. Rice plants at the tillering stage were selected, washed, cut into stems of approximately 25 cm in length, and dried in the shade. These were soaked in the experimental insecticide solutions for 30 s, then dried and placed in glass tubes (300 mm height × 30 mm diameter) placed horizontally and open at both ends. Twenty healthy nymphs of similar size were selected and placed in the glass tubes, which were then placed upright after all nymphs climbed onto the rice stems. The experimental conditions were as follows: temperature 25 ± 1 °C, relative humidity 70 ± 10%, and illumination 16:8 in an artificial climate chamber for 48 h. At this point, the number of dead insects was counted. A toxicological regression equation was fitted using the Probit model in SPSS 22.0, and LC₁₀, LC₂₅, LC₅₀, and LC₉₀ were calculated.