Strengthening plant defenses: Microbial and micronutrient contributions from fertilizers

Corn productivity is frequently challenged by herbivorous insects, which threaten plant growth and significantly reduce yields. Fertilizer treatments, particularly those introducing microbial communities, macro and micro- nutrients, play a critical role in modulating plant resistance to herbivores and influencing insect performance. Our study investigates the impact of fertilizer treatments on corn plant resistance and herbivore performance, focusing on the role of microbial communities and micronutrient availability. We hypothesize that fertilizers containing microbial communities and micronutrients enhance plant defense responses, leading to reduced herbivory and decreased insect performance. Using a controlled greenhouse experiment, we compared corn grown in potting media treated with five fertilizer options: (1) intact microbial communities from dry-stacked manure, (2) sterilized manure supplemented with 5 % of live manure, (3) sterilized manure, (4) Micronutrient+NPK nutrient solution, and (5) NPK solution. After 4 weeks of growth, we allowed black cutworm (Agrotis ipsilon) caterpillars to feed on these plants for 7 days. We found that microbial communities and micronutrients influence insect performance and levels of herbivory. Manure treatments rich in microbes and nutrients appeared to enhance plant defenses more effectively than inorganic fertilizers. These results highlight the dual role of manure not only as a nutrient source but also as a key factor in modulating plant-insect interactions, supporting its potential use in sustainable pest management strategies.