# Examining the Effects of Induced Plant Defenses on _Spodoptera frugiperda_ Performance
## 4 Discussion  
Our results indicate that plant cultivar and JA induction were both important initial causes of mortality at 7 days for insects. However, contrary to our expectations, although plant cultivars varied in their amounts of constitutive/inducible phenolic compounds and POD, plant induction and cultivar did not cause an interactive effect (Figure 1; Table 1). POD produces deleterious reactive oxygen species harming insects but also uses phenolic compounds as a substrate, producing toxins like quinone and quinone methides, which can bind to plant-derived amino acids reducing their digestibility [24; 31]. Given the results, it would seem _S. frugiperda_ is not capable of mounting an effective strategy against POD at these early life stages. Interestingly, the Braxton cultivar exhibited a 9.6% decrease in insect survival when JA was applied, even though this cultivar does not express higher amounts of phenolic compounds or POD when induced with JA [24]. Thus, our results also indicate that other plant secondary metabolites or structural defenses, such as protease inhibitors (PIs) or trichomes [32; 33; 34; 35], are important contributors to plant defense against general insects concerning soybeans. Specifically, for the soybean cultivars we investigated, PIs have also been implicated in lowering insect pest performance [26; 36]. Insect development to pupation was also extended when fed on induced plants and by cultivar, although the latter only marginally (Figure 2; Table 2). Again, cultivar and JA induction did not interact even though cultivars varied in their amounts of constitutive and inducible phenolics/POD, which can be seen by the main effects model being considerably better than the main interactive effects model (Tables 2 and S2A,B). Although there did seem to be a trend for interaction between cultivar and sex on pupal mass (Table S3A), the better fit main effects models to these data suggest pupal mass was only marginally influenced by plant cultivar (Figure 3; Table S3B). This difference is likely not biologically relevant, though, comprising less than a one percent difference in average mass. Induction also did not impact pupal mass regardless of the model. This outcome is perhaps not surprising since the impetus to pupate rather than molt into a new instar is hormonally coordinated  
Figure 4: Regression of total number of eggs laid by _S. frugiperda_ females (_y_-axis, back-transformed to linear) using female pupal mass (mg) as the predictor (_x_-axis). Heavier females laid more eggs than lighter females. Filled circles represent the raw data, with the solid black line representing the regression and the dashed red lines represent the 95% credible intervals. and contingent on a genetically set fixed size/mass rather than development time [37]. Insects, especially lepidopterans like the fall armyworm, can have supernumerous instars to meet their target pupal mass due to poor quality food or varying temperatures. Lastly, the total number of eggs laid by females was influenced by female pupal mass (Figure 4; Table 4). This is also not unsurprising since heavier females are bigger and thus have more space/resources to develop eggs over their adult lifespan compared to lighter/smaller females. Although, our data also suggest females lay \(\sim\)100 eggs regardless of their mass, with heavier females perhaps laying the same number of eggs but allocating more resources to each one. Work by [PERSON] et al. (2021) [38] would suggest the former hypothesis, with female mass influencing fecundity and the variability in our data being perhaps attributed to the fewer number of male copulatory partners. From a management perspective, plant cultivar and inducible JA defenses had the strongest effects on early larval mortality, which would be the most susceptible and naive life stages to plant defenses.