Lethal time analysis reveals contrasting insecticide performance against Spodoptera frugiperda
The fall armyworm, Spodoptera frugiperda (Smith, 1797), is a major agricultural pest worldwide because of its polyphagous feeding habits, broad geographic distribution, and high adaptive capacity. Although maize is its primary host, the species can attack more than 350 plant species across 76 botanical families, causing substantial yield losses in several cropping systems. This study evaluated the efficacy of chemical and biological insecticides against S. frugiperda by assessing larval mortality, median lethal time (LT₅₀), and the time required to achieve 90% mortality (LT₉₀) in second- and third-instar larvae. The experiment was conducted at the Integrated Pest Management Laboratory of the Federal University of Santa Maria (LabMIP–UFSM), Brazil, between May and June 2023, using a completely randomized design with five insecticide treatments (Cartugen®, Dipel®, Exalt®, Prêmio®, and Lannate®), an untreated control, and ten replicates. All evaluated insecticides significantly increased larval mortality compared with the untreated control. Lannate® exhibited the highest efficacy, reaching 50%, 90%, and 100% mortality of second-instar larvae approximately 15, 23, and 30 h after application, respectively, whereas the same mortality levels in third-instar larvae were achieved after approximately 23, 40, and 42 h. Biological insecticides also provided effective control; however, their insecticidal activity was slower than that of the chemical insecticides. Overall, chemical insecticides showed superior performance in both larval stages, with Lannate® standing out as the most effective treatment. These findings provide robust experimental evidence to support insecticide selection and contribute to more effective and sustainable integrated pest management programs for S. frugiperda.