Efficacy of the insect biocontrol fungus Beauveria bassiana towards the European corn borer feeding on treated maize leaf and stalk tissue is inbred dependent and associated with resistance to the maize pathogen Fusarium

Authors: Dowd, Patrick; Johnson, Eric

Submitted to: International Journal of Plant Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/18/2024
Publication Date: 7/19/2024
Citation: Dowd, P.F., Johnson, E.T. 2024. Efficacy of the insect biocontrol fungus Beauveria bassiana towards the European corn borer feeding on treated maize leaf and stalk tissue is inbred dependent and associated with resistance to the maize pathogen Fusarium. International Journal of Plant Biology. https://doi.org/10.3390/ijpb15030049.
DOI: https://doi.org/10.3390/ijpb15030049

Interpretive Summary: Insects greatly reduce corn yields, and are associated with corn ear molds that can produce toxins harmful to people and animals. This is causing hundreds of millions of dollars in losses in the U.S. alone. Biological control of insect pests is a sustainable and safe method of insect management, but variability in effectiveness impedes adoption, which may be due to plant variety effects. Different plant varieties were found to greatly affect rate of kill for commercially available strains of insect biological control fungi, in both leaf and stalk tissue. This knowledge can be used to help guide the development of more effective combinations of plant varieties and biological control organisms, thereby enhancing yield, quality and safety.

Technical Abstract: Plant resistance mechanisms to pathogens can lead to lowered efficacy of insect biocontrol agents. Leaves and stalks from twelve maize (Zea mays L.) inbreds previously demonstrating a differential effect on the efficacy of two commercial strains of Beauveria bassiana (Bals.-Criv.) Vuill. against corn earworms (Helicovepa zea (Boddie)) and fall armyworms (Spodoptera frugiperda (J.E. Smith)) were evaluated for their influence on the efficacy of B. bassiana against European corn borers (Ostrinia nubilalis (Hübner)) as compared to fall armyworms. For leaf assays with first instar caterpillars, mortality on day 2 ranged from an inbred dependent high of 87.5% and 76.1% to a low of 22.1% and 10.0% for fall armyworms and European corn borers, respectively in leaf assays. For stalk assays with third instar caterpillars, mortality on day 4 ranged from an inbred dependent high of 83.0% and 75.0% to a low of 0.0% and 8.3% for fall armyworms and European corn borers, respectively. Relative efficacy ranking of specific inbreds was often different for the two insect species for leaves and stalks. Lesion size ratings due to Fusarium graminearum (Schwabe) applied to tissues were often significantly correlated with the mortality levels of both species of B. bassiana treated caterpillars that fed on leaves and stalks, suggesting that maize resistance factors to F. graminearum impeded the efficacy of B. bassiana in both tissue types. This study suggests that the influence of plant varieties on the efficacy of insect pathogens can vary depending on the insect species involved and the plant tissue, and it is worth considering when new plant varieties and biocontrol strains are being developed whenever practical.