Different maize (Zea mays L.) inbreds influence the efficacy of Beaveria bassiana against major maize caterpillar pests, which is potentially affected by maize pathogen resistance

Plant resistance factors, such as secondary metabolites and proteins, are known to affect the viability of insect fungal pathogens. Different plant varieties can have different levels of plant pathogen resistance, which could potentially influence efficacy of insect pathogens. Leaves from twelve maize (Zea mays L.) inbreds with different reported resistance to Fusarium and/or Aspergillus pathogens were examined for their influence on the efficacy of two different commercial strains of Beauveria bassiana (Bals.-Criv.) Vuill. against corn earworms, Helicovepa zea (Boddie) and fall armyworms, Spodoptera frugiperda (J.E. Smith). For leaf assays with first instar caterpillars, mortality on day 2 ranged from an inbred dependent high of 92% to a low of 14% for corn earworms, and from a high of 84% to a low of 22% for fall armyworms. Leaves that caused the greatest inhibition of 8. bassiana efficacy had the greatest amount of caterpillar damage compared to corresponding control leaves that were not treated with B. bassiana. Damage ratings due to Fusarium graminearum (Schwabe) infection were often correlated with the mortality levels of both species of B. bassiana treated caterpillars that fed on leaves, suggesting that maize resistance factors to F. graminearum were interfering with the efficacy of B. bassiana. The study suggests that the interaction between plant pathogen resistance factors and insect pathogens should be considered when developing both new plant varieties and biocontrol strains that may be used for insect pest management where possible.