Response of Spodoptera frugiperda Larval Instars to Commonly Used Insecticides in Tanzania

Fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), is a polyphagous migratory pest reported in Tanzania in 2017. Limited choices of officially registered insecticides for the control of the pest when it first occurred led to many farmers opting for the few available ones including those that were not registered for the pests. The current study drew from a survey conducted in 2018 that listed the insecticides commonly used by farmers against the pest. The study assessed the effectiveness of the insecticides against the different S. frugiperda larval instars under field conditions in the 2019 and 2020 growing seasons. Ten commonly used insecticides were applied to S. frugiperda damaged maize crops. Obtained results suggested a varied effectiveness of the tested insecticides with some inflicting significant (p < 0.001) mortality of S. frugiperda larvae while some proved ineffective. Ninja plus 5EC, Profecron 720 EC, Multi alpha plus 150 EC and Duduba 450 EC, caused highest mortality of S. frugiperda in all experimental plots accompanied with reduced incidences and damage severities on maize crops while Thunder 145 OD and Attakan 350 SC were the least effective. Yields obtained from the experiments suggested a significant impact of applied insecticides whereby plots treated with Duduba 450 EC produced the highest yield (4 tons/ha) compared to non-treated plots (2.2 tons/ha).  The findings from this study prove that some insecticides were effective against the pest while some were not. As such farmers’ complaints on the ineffectiveness of traded insecticides could be real.