Patogenicidade e virulência de isolados de Bacillus thuringiensis a Spodoptera frugiperda

Abstract

Caterpillars of the Spodoptera complex are polyphagous insects that cause significant damage to the agricultural sector. Among the species of greatest economic importance are Spodoptera frugiperda, S. eridania, and S. cosmioides. Biological control using entomopathogenic bacteria represents a viable strategy for insect pest management, and the search for new pathogenic and virulent isolates is essential for the development of new products. In this context, the present study aimed to evaluate the pathogenicity and virulence of different Bacillus thuringiensis isolates against S. frugiperda caterpillars. For this purpose, five B. thuringiensis isolates (BR 139, BR 67, BR 94, BR 58, and BR 33), obtained from the entomopathogen collection of the State University of Londrina, were evaluated against first-, second-, and third-instar S. frugiperda larvae. The isolates were propagated in the laboratory from stock cultures, and standardized suspensions were subsequently prepared at a concentration of 1 × 10⁸ UFC/mL. From these suspensions, 50 μL were micropipetted and applied onto the artificial diet for larvae in acrylic plates containing 12 wells, using 50 μL per well. After evaporation of excess moisture, one first-, second-, or third-instar larva was individually placed into each well. Subsequently, the plates were maintained in a climate-controlled chamber at 27 ± 2 °C, relative humidity of 70 ± 5%, and a 14-hour photophase. Evaluations were conducted daily for five days, recording the number of dead larvae. Surviving larvae were monitored daily until pupation and adult emergence.For each treatment (isolate), five replicates were used, consisting of plates containing 12 wells, totaling 60 larvae per treatment. The isolates did not show significant pathogenicity against first-, second-, and third-instar larvae, and no significant differences were observed compared with the control treatment.