Entomopathogenic Nematodes Induce Metabolic Reallocation in Maize Roots Without Altering the Performance of Two Root Herbivores, <i>Diabrotica virgifera</i> and <i>Diabrotica balteata</i>

Entomopathogenic nematodes (EPNs) are key biological control agents in agriculture, but their direct effects on plant metabolism and resistance to herbivory remain underexplored. By combining transcriptomic, metabolomic, and herbivore assays, this study aimed at providing a holistic description of maize root responses to EPNs and to assess their potential relevance for plant-herbivore interactions. EPNs triggered a dynamic shift in root metabolism, suggesting a reallocation of primary resources towards chemical defences. After 72 h, pathways related to ethylene signalling and protein folding, and turnover were downregulated, while pathways for protein export were enriched. Amino acid levels, particularly glutamate and aspartate, decreased, while glucose levels were induced. In parallel, enrichments in alpha-linolenic acid metabolism, glycan biosynthesis, and, albeit not significantly, cutin, suberine, and wax biosynthesis pathways suggested enhanced barrier functions and lipid signalling. Secondary metabolite concentrations, such as benzoxazinoids, were increased. Yet, the overall plant response remained of modest magnitude, as illustrated by a low number of differentially expressed genes exceeding 100 reads. Consistently, EPN exposure did not enhance resistance to subsequent herbivory by the root herbivores Diabrotica balteata or Diabrotica virgifera virgifera. However, the plant responses might influence other belowground interactions, such as those involving plant-microbes or plant-parasitic nematodes, calling for further investigations.