Concentration-Related Mortality of Spodoptera Frugiperda Larvae Treated With Bacillus Thuringiensis and Beauveria Bassiana

Abstract

The fall armyworm, Spodoptera frugiperda, is a serious crop pest for which microbial control agents warrant laboratory evaluation. This study described larval mortality associated with three concentrations of Bacillus thuringiensis spore suspensions and Beauveria bassiana conidial suspensions. The study was conducted from June to August 2026 at the Plant Disease Laboratory, Faculty of Agriculture, Sam Ratulangi University, Indonesia. The reported completely randomized design comprised one control and six microbial treatments, with three replicates of ten larvae per treatment (210 larvae in total). Suspensions were applied by direct spraying at 1 × 10⁷, 1 × 10⁸, and 1 × 10⁹ spores/mL for B. thuringiensis or conidia/mL for B. bassiana. The bioassay lasted seven days. Across the three concentrations, reported mortality was 53.3%, 76.7%, and 93.3% after B. thuringiensis treatment, compared with 46.7%, 66.7%, and 83.3% after B. bassiana treatment. Thus, mortality increased numerically with concentration within each microbial treatment series. However, control mortality, the basis for aggregation across replicates, and details of the microbial preparations were not reported in the available study record. Consequently, these results should be interpreted descriptively and do not establish statistical superiority or equivalent biological potency between bacterial spores and fungal conidia. The observations support further, more completely documented bioassays of these microbial preparations for fall armyworm management