Baseline Susceptibility of Eldana saccharina to CORAGEN® SC: Implications for Resistance Monitoring and Management in Sugarcane

Eldana saccharina Walker is one of the most destructive sugarcane pests in South Africa. The application of chemical pesticides mainly controls this pest; however, the resistance in pest populations threatens the effectiveness of these pesticides. Laboratory bioassays were conducted at the South African Sugarcane Research Institute to assess the baseline susceptibility of E. saccharina against different concentrations (0.005, 0.014, 0.024, 0.033, 0.041 and 0.049 µg/ml) of CORAGEN® SC (chlorantraniliprole) insecticide. Two-day-old larvae were inoculated into an artificial diet with CORAGEN® SC solution. Daily monitoring of larval feeding and movement behaviour on the diet was performed for seven days, and the mortality rate and larval weight data were determined. The data was subjected to probit analysis using IBM SPSS version 27 to determine a lethal concentration (LC₅₀) of the E. saccharina population and its 95% confidence limits. Differences in mortality and larval weight across different concentrations were assessed using a one-way ANOVA in IBM SPSS. Tukey’s multiple comparisons were used to assess differences in larval mortality and weight between concentration groups. The study showed that mortality increases progressively from the lowest to the highest concentration. The highest concentration (0.049 µg/ml) resulted in 79% mortality, while the control (15%) exhibited minimal effects. Additionally, larval weight decreased as concentration increased, with the control having the highest mean weight (8 mg) and the highest concentrations (0.041 and 0.049 µg/ml), resulting in the lowest weight (0.2 mg). The LC50 value was 0.0298 ug/ml with a 95% CI of 0.0252 - 0.0353 ug/ml. The results demonstrated a positive correlation between insecticide concentration, mortality rate and larval weight reduction. These findings provide crucial data for resistance monitoring, aiding in developing sustainable pest management strategies for sugarcane production. This study could further serve as a foundation for developing an IRAC laboratory-based resistance monitoring protocol.