Five-year monitoring of cotton leafhoppers (Hemiptera: Cicadellidae) in Côte d’Ivoire (2021–2025): population dynamics, damage intensity, and agronomic determinants

Abstract Background Since 2022, cotton production in Côte d’Ivoire has been severely challenged by a sharp increase in leafhopper infestations, with the invasive species Amrasca biguttula accounting for 98–100% of the jassids collected on cotton. This study aimed to quantify jassid pressure over five consecutive years and identify the main agronomic factors associated with population dynamics and crop damage under farmer-managed conditions. Results A five-year monitoring program (2021–2025) was conducted in 59 cotton-growing localities and 2,693 farmer-managed plots. The jassid population was assessed weekly from 30 to 122 days after emergence as the mean number recorded on the five terminal leaves of 30 plants per plot, whereas damage was measured as the number of attacked plants out of 30. Jassid population and damage varied significantly among years, with peak damage recorded in 2022, and both were consistently higher in the northern cotton belt (≥ 9°N) than in the south. Cotton variety and previous crop were the most consistent determinants of the infestation and damage. The sowing decade had limited effects in the univariate analyses but became significant for the population in the multivariate model. Increasing the number of insecticide treatments did not reduce infestation and was positively associated with jassid pressure, whereas longer spray intervals were associated with reduced fruit damage. Damage intensity, but not population density, was negatively correlated with seed cotton yield. Conclusion These findings show that jassid risk in Côte d’Ivoire is strongly structured by year, region, variety, and cropping history, and that damage-based indicators are more informative than insect counts for assessing agronomic impact. Effective management should therefore rely on spatially differentiated and integrated strategies that prioritize tolerant varieties, appropriate crop rotations, and optimized spray scheduling rather than generalized spray intensification.