Above- and belowground resistance in Brazilian maize varieties under attack of Spodoptera frugiperda and Diabrotica speciosa

In South America, maize (Zea mays L., Poaceae) crops are commonly infested with larvae of Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae), known as voracious leaf feeders, as well as by larvae of Diabrotica speciosa (Germar) (Coleoptera: Chrysomelidae), a pest that destroys maize root systems. Despite the relevance of these insects to maize fields, there is no information available about the effects of these herbivores on one another. Therefore, this study aimed to evaluate in different maize varieties: (1) the influence of previous leaf consumption by S. frugiperda on D. speciosa larval weight and survival, (2) effects of previous root attack by D. speciosa on S. frugiperda larval weight and survival, and (3) the relationship between peroxidase and superoxide dismutase (resistance-related enzymes) and maize resistance to the pests. One fifth instar S. frugiperda was released per potted maize plant at vegetative stage 4 (V4), and 24 h later plants were infested with 25 D. speciosa larvae. One set of plants was infested with D. speciosa only, and 16 days later whorl leaf sections were brought to the laboratory and offered to S. frugiperda neonate larvae. Performance of both insect pests was determined based on larval weight and survival. Uninfested plants of variety Maisena were susceptible to both herbivores. However, plants of this variety pre-infested with S. frugiperda disfavored D. speciosa larval survival. Similarly, plants of variety Maisena pre-infested with D. speciosa adversely affected S. frugiperda larval growth. Nevertheless, this induction of resistance was inhibited when the plant was also pre-infested with S. frugiperda. In most cases, peroxidase and superoxide dismutase did not seem to play a role in mediating resistance to the pests. Overall, variety Maisena appears as a template for the development of maize genotypes expressing induced resistance. The potential of some varieties regarding constitutive resistance is also discussed.