Cannabidiol reduces fall armyworm ( Spodoptera frugiperda ) growth by reducing consumption and altering detoxification and nutritional enzyme activity in a dose-dependent manner

Plant quality can shape plant–insect interactions and plant secondary metabolites are known to play an influential role in mediating these interactions. Cannabinoids are a group of terpenophenolic compounds in Cannabis that have demonstrated negative effects on insect herbivores, yet specific mechanisms are currently not well understood. Insects can modulate their rate of growth, food intake, or production of frass (i.e., insect feces) to mitigate consumption of a diet with poor nutritional quality. Detoxification and nutritional enzymes are essential in performing these functions. To test how cannabinoids impact insect performance and enzymatic activity, we performed no-choice feeding bioassays on fall armyworm ( Spodoptera frugiperda ) with artificial diet spiked with different concentrations of CBD and measured fall armyworm growth, consumption, and frass production and analyzed detoxification and nutritional enzyme activities. We found that as CBD concentration increased fall armyworm growth and consumption decreased, but found no impact on digestibility or conversion efficiencies. Results from the enzymatic assays varied, but CYP450 and protease activity decreased, while glucosidase activity increased, as CBD concentration increased. Relationships among enzyme activities suggest that a reduction in protease activity might limit a detoxification response, by limiting amino acid availability needed for detoxification enzyme production, even though energy collection activity, via increased glucosidase activity, occurred. These outcomes suggest specific mechanisms by which CBD has a negative influence on insect herbivore performance.