Interaction between the entomopathogenic bacterium Bacillus thuringiensis subsp. kurstaki and two entomopathogenic fungi in bio-control of Sesamia nonagrioides (Lefebvre) (Lepidoptera: Noctuidae)

The interactions between the entomopathogenic bacterium Bacillus thuringiensis ssp. kurstaki and two entomopathogenic fungi Beauveria bassiana Balsamo (Vuillemin) (Hypocreales: Cordycipitaceae) and Metarhizium robertsii (Metchnikoff) Sorokin (Hypocreales: Clavicipitaceae) were examined on larvae of Sesamia nonagrioides (Lefebvre) (Lepidoptera: Noctuidae) in 8, 13 and 16 days post-treatment intervals. An overall positive interaction between the pathogens was observed and the larval mortality at 16 days was 56–100 % exposed to M. robertsii combined with B. thuringiensis subsp. kurstaki, whereas B. bassiana combined with B. thuringiensis ssp. kurstaki killed 54–100 % of exposed larvae. After 8 days, in 6 of the combinations, we found an additive relationship between the pathogens, whereas, a negative interaction was observed in 10 of them. In contrast, after 13 days, in 2 of the combinations the positive interaction could be considered as synergistic between pathogens, in 10 as additive, and in only 4 as negative. Finally, after 16 days, in 11 of the combinations we found an additive connection between the pathogens, wheras a negative interaction was seen in 5. Applying both pathogens simultaneously offers a method of Sesamia nonagrioides control that could be more effective than using each pathogen separately.