Antibiotic susceptibility and functional enzyme profiling of gut bacteria isolated from fall armyworm (Spodoptera frugiperda) feeding on maize

Abstract

The fall armyworm (Spodoptera frugiperda) is a highly destructive invasive pest of maize with remarkable adaptability to diverse agroecosystems. Increasing evidence suggests that gut-associated bacteria play a crucial role in insect nutrition, digestion, and tolerance to environmental stressors, including antimicrobial compounds. The present study aimed to isolate cultivable gut bacteria from fall armyworm larvae feeding on maize and to characterize them based on antibiotic susceptibility patterns and functional enzymatic activities. Seventeen bacterial isolates were recovered from larval gut homogenates and subjected to antibiotic susceptibility testing against erythromycin, colistin, polymyxin, nadifloxacin, methicillin, and rifampicin using the disc diffusion method. Functional characterization included screening for protease and urease activities. The isolates showed high susceptibility to nadifloxacin (88.2%), followed by colistin and polymyxin (64.7%), whereas resistance was frequently observed against methicillin and erythromycin. One isolate exhibited resistance to all tested antibiotics. Protease activity was detected in six isolates, with the highest activity recorded in FWG-14 (22.66), while urease activity was observed in six isolates (35.3%). The coexistence of antibiotic resistance and functional enzyme production highlights the ecological and physiological significance of gut bacteria in fall armyworm nutrition and adaptability. These findings provide insights into insect-microbe interactions and may contribute to the development of microbiome-based pest management strategies.