Biocontrol potential of Bacillus thuringiensis subsp. aizawai GC-91 (Bacillales: Bacillaceae) against Spodoptera eridania (Stoll, 1782) (Lepidoptera: Noctuidae)

Spodoptera eridania (Stoll, 1782) (Lepidoptera: Noctuidae) is an insect pest that affects several crops in Brazil, causing yield losses. Traditional larval control relies on synthetic insecticides, which may harm the environment and non-target organisms. Thus, sustainable alternatives are needed. Bacillus thuringiensis (Bacillales: Bacillaceae) (Bt) is an entomopathogenic bacterium widely used in bioinsecticides due to its specificity and safety. This study evaluated the biocontrol potential of Bt subsp. aizawai GC-91 against S. eridania neonates and its effects on the midgut. Four concentrations of a commercial product: (0.62, 1.25, 2.50, and 5.00 g/L −1 ) corresponding to 23.6, 47.5, 95, and 190 µg/mL of insecticidal proteins, respectively, were incorporated into an artificial diet and offered to larvae. Mortality was recorded every 24 for 168 h, and midgut samples were collected at 24 and 48 h. Concentrations of 1.25, 2.50, and 5.00 g/L −1 resulted in 100 % mortality after 168 h, with lethal concentrations estimated at LC 50 = 0.35 g/L −1 (CI = 0.27–0.43) and LC 90 = 0.64 g/L −1 (CI = 0.55–0.76). Histological and ultrastructural analyses revealed midgut alterations at both time points including projections of columnar cells into the lumen, vesiculation, displacement of the basal lamina, and intercellular and intracellular spacing. These results demonstrate that Bt subsp. aizawai GC-91 has strong entomopathogenic activity against S. eridania larvae, severely damaging their midgut. Therefore, this bacterium represents an efficient and promising alternative for the sustainable control of this polyphagous pest in different crops.