Responses of cotton jassid (Amrasca biguttula) to synthetic insecticides recommended in Tanzania

Introduction: ) have emerged as the most damaging sucking pest in cotton production in Tanzania, causing yield losses of up to 50% when unmanaged. Control has largely depended on synthetic insecticides; however, their effectiveness has been questioned by growers. It remains unclear whether this reduced efficacy is due to inherent properties of the insecticides or to external factors such as application rate, timing, and method. Methods: Replicated field experiments were conducted at three locations within the Western and Eastern Cotton Growing Areas (WCGA and ECGA) of Tanzania during the 2024-2025 growing season. Four commonly recommended insecticides: Lambda-cyhalothrin, Chlorpyrifos, Imidacloprid, and Profenofos were evaluated alongside an untreated control using a randomised complete block design (RCBD). Applications were based on the economic threshold level (ETL = 1-2 jassids per plant) at 10 -14 day intervals. Mortality was assessed at 24, 48, and 72 hours post-application, and population reduction was calculated using Abbott's formula. Data were analysed using analysis of variance (ANOVA), with means separated using Duncan's Multiple Range Test (DMRT) at 95% confidence. Results: All tested insecticides significantly reduced both nymph and adult jassid populations compared to the control, although their efficacy varied. Imidacloprid was the most effective, achieving mean reductions of 67.59% (nymphs) and 66.31% (adults), followed by profenofos with reductions of 52.75% (nymphs) and 55.83% (adults). Discussion: The results demonstrate that insecticide effectiveness varies considerably, with Imidacloprid showing superior performance under field conditions. These findings suggest that its inclusion in integrated pest management (IPM) programmes could improve jassid control. However, optimisation of application practices remains essential to enhance overall efficacy and sustainability.