Multitrophic interactions between maize mycorrhizas, the root feeding insect Phyllophaga vetula and the entomopathogenic fungus Beauveria bassiana

Root feeding larvae of Phyllophaga vetula causes severe damage in maize agroecosystems and their conventional management with chemical pesticides adversely affects the environment. Plant beneficial rhizosphere microorganisms such as mycorrhzial and entomopathogenic fungi (EPF) offer an alternative sustainable pest management strategy, but their successful integration in agroecosystems requires profound knowledge about their ecology. Here we explored interactions between a commercial isolate of the EPF Beauveria bassiana and indigenous maize mycorrhizas and their single and combined effects against root herbivory from the insect larvae P. vetula. Maize plants were grown in a greenhouse for seven weeks in pots with P limited soil with all possible combinations of the three main factors including native arbuscular mycorrhizal fungi (AMF) (without and with), EPF (without and with) and P. vetula (without and with).Root herbivory by P. vetula reduced plant growth and nutrition, and in addition reduced AMF root colonization. In contrast, AMF improved plant growth and P nutrition, but also reduced the population density of B. bassiana. Inoculation with B. bassiana increased root dry weight and counteracted a decrease in shoot N content from P. vetula root herbivory, despite that only 5% of P. vetula larvae were infected with B. bassiana. Dual inoculation with AMF and B. bassiana increased plant growth and N shoot content allowing the plants to compensate for the damage caused by P. vetula herbivory. In conclusion our results show that combination of native AMF populations and the EPF B. bassiana induce tolerance in maize from root herbivory by P. vetula in terms of plant growth performance and nutrition.