Effects of Methyl Jasmonate Fumigation on the Growth and Detoxification Ability of Spodoptera litura to Xanthotoxin

SIMPLE SUMMARY: Methyl jasmonate (MeJA) is a volatile substance derived from jasmonic acid (JA), and it responds to biotic and abiotic stresses by participating in interplant communication. Because MeJA is hydrophobic and it can easily move between plant cells, it is considered a propagable form of JA, which can utilize this method to induce plant defenses. Pests are able to ‘eavesdrop’ on plant signal molecules as cues for activating the detoxification system to protect themselves from plant defenses, and insects have evolved a variety of mechanisms to metabolize, sequester, or detoxify plant toxins. Spodoptera litura is an omnivorous insect that damages a variety of crops worldwide. We analyzed the growth of S. litura and its detoxification ability against xanthotoxin after exposure to different concentrations of MeJA fumigation, and the effective role of MeJA in inducing insects’ defense response to the toxin was studied. We demonstrated that MeJA is effective at inducing S. litura defense response by increasing its detoxifying enzyme activities, but the enhanced detoxifying ability could not overcome the strong toxins. ABSTRACT: Methyl jasmonate (MeJA) is a volatile substance derived from jasmonic acid (JA), and it responds to interbiotic and abiotic stresses by participating in interplant communication. Despite its function in interplant communication, the specific role of MeJA in insect defense responses is poorly understood. In this study, we found that carboxylesterase (CarE) activities, glutathione-S-transferase (GSTs) activities, and cytochrome mono-oxygenases (P450s) content increased more after the feeding of diets containing xanthotoxin, while larvae exposed to MeJA fumigation also showed higher enzyme activity in a dose-dependent manner: lower and medium concentrations of MeJA induced higher detoxification enzyme activities than higher concentrations of MeJA. Moreover, MeJA improved the growth of larvae fed on the control diet without toxins and diets with lower concentrations of xanthotoxin (0.05%); however, MeJA could not protect the larvae against higher concentrations of xanthotoxin (0.1%, 0.2%). In summary, we demonstrated that MeJA is effective at inducing S. litura defense response, but the enhanced detoxifying ability could not overcome the strong toxins.