Maize resistance to Spodoptera frugiperda and its relationship to landrace variety, plant stage, and larval origin

Abstract

Previous studies have raised the hypothesis that laboratory‐reared insects may lose their ability to induce plant defenses because induction‐associated gut bacteria may be eliminated by antibiotics used in artificial diets. The present study was conducted to determine whether maize (Zea mays L., Poaceae) responses to Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae) differ when field‐collected vs. laboratory‐reared insects are feeding. One fifth instar from the laboratory or field was released onto a resistant or a susceptible landrace variety at vegetative stages 4 and 6 (V4 and V6), or plants remained uninfested. Five days later, damage was estimated and sections of maize leaves were fed to forth instars in a Petri dish assay to assess the effects of previous feeding on weight gain, leaf consumption, and nutritional indices of conspecifics. Initially, field‐collected larvae caused more damage on V4, but not on V6 maize plants, than laboratory‐reared larvae. In V6 plants, the resistant variety showed less leaf damage than the susceptible variety. In a Petri dish assay, there were no differences between effects of laboratory‐reared and field‐collected larvae on the measured parameters, but larvae from both sources promoted increased susceptibility in maize plants at the V4, but not the V6 stage. This was characterized by higher weight gain and higher efficiency of conversion of ingested food (ECI) (on both maize varieties), and lower metabolic cost (MC) (on one variety) when S. frugiperda larvae fed on leaves pre‐infested with laboratory‐reared larvae compared to leaves of uninfested plants. Conversely, S. frugiperda larvae fed on leaves pre‐infested with field‐collected larvae consumed a greater amount of leaf tissue (on both varieties) compared to leaves of uninfested plants. A similar experiment with neonates showed no effects of landrace variety or previous infestation on insect weight and survival, but insects obtained a higher body weight when fed on V4 compared to V6 plants. In conclusion, S. frugiperda laboratory‐reared larvae were equally able as field‐collected larvae to induce susceptibility in V4 maize plants, and maize plants were more resistant to the pest at the V6 than at the V4 stage.

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

“…Although D. speciosa larval feeding on roots of Maisena induced resistance to S. frugiperda, this resistance was lost when the maize plants were subjected to a double infestation (S. frugiperda and D. speciosa), as observed in the results of larval weight. This finding is in agreement with Costa et al (2021) who reported that previous S. frugiperda larval feeding impairs resistance of V4 Maisena plants to subsequent infestation of conspecifics. In contrast, no S. frugiperda larvae survived when fed on Pérola plants under double infestation, whereas Pipoca preserved its resistance unchanged compared to uninfested plants.…”

“…Nevertheless, SOD production was inhibited in Maisena leaves when also pre‐infested with S. frugiperda (double infestation). This was possibly an example of induced susceptibility, mediated by previous S. frugiperda leaf feeding, similar to an observation made for Maisena by Costa et al (2021).…”

“…Four maize varieties were tested – Maisena, Pérola, Asteca, and Pipoca. Maisena was used because it showed resistance to S. frugiperda in a previous experiment (Costa et al, 2021) using vegetative stage 6 (V6) maize plants, the stage at which the plant exhibits six fully expanded leaves (Ritchie et al, 1993). Pérola was chosen because it negatively affected growth and survival of S. frugiperda (Nogueira et al, 2019) and D. speciosa (Costa et al, 2018).…”

“…Importantly, V4 stage is included in the period V4–V8, in which maize plants were regarded as more susceptible to S. frugiperda larval feeding (Cruz, 1995). Plants were tested at V4 stage due to their greater susceptibility to S. frugiperda larval attack compared to V6 maize plants, as presented by Costa et al (2021).…”

“…In this work, four Brazilian maize varieties were tested, the only representatives from South American continent in terms of published studies on aboveground-belowground interaction involving S. frugiperda and D. speciosa. The maize varieties studied were: Maisena, resistant to S. frugiperda (Costa et al, 2021); Pérola, resistant to S. frugiperda and D. speciosa (Costa et al, 2018(Costa et al, , 2020Nogueira et al, 2019); Asteca, a variety commonly planted by small farmers in Mato Grosso do Sul state; and Pipoca, a variety from a popcorn commercial group, which had no representative in the study by Gill et al (2011), where above-and belowground resistance of maize genotypes were evaluated for the interaction between S. frugiperda and D. v. virgifera. Lastly, we evaluated effects of a previous double infestation (S. frugiperda and D. speciosa) on S. frugiperda larval weight and survival, i.e., not only effects of a single infestation.…”