Laboratory evaluation of the entomopathogenic fungus Beauveria bassiana, bacterium Bacillus thuringiensis, and insecticide emamectin benzoate treatments, alone and in dual combinations against Spodoptera frugiperda

Spodoptera frugiperda , the fall armyworm (FAW), is a major global pest of different crops and especially maize, posing significant challenges due to its rapid spread and adaptive biology. The current investigation evaluated the effect of three insecticidal agents— Beauveria bassiana ( Bb ), Bacillus thuringiensis ( Bt ), and emamectin benzoate (eb)—applied alone and in respective dual combinations ( Bb + Bt, Bb + eb, Bt + eb) against 3 rd and 5 th instar larvae of FAW. Results showed that the Bb + eb combination consistently induced the highest mortality (92.6 %), disrupted developmental parameters, reduced egg eclosion (15.0 %), and adult emergence (19.4 %), compared to the other treatments and controls. Sublethal doses of this combination prolonged larval and pupal durations (21.2 and 12.2 days, respectively) and significantly decreased adult longevity (9.4 days) compared to the other treatments and controls. These results suggest the potential of integrating chemical and microbial agents to improve pest control while moderating the chemical input. These findings support the strategic use of combined treatments targeting the development of FAW and offering a promising potential strategy for sustainable pest management. • Evaluation of dual combinations of three insecticidal agents against FAW larvae • Bb + eb caused 92.6% larval mortality, the highest among all treatments • Bb + eb and Bt + eb significantly increased mortality vs. the single treatments • Bb + eb reduced adult longevity to 9.4 days vs. 12.3 days in the control • All combinations reduced pupation, but Bb + eb had the lowest rate (13.9%)