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Effect of cannabidiol on fall armyworm performance and enzyme activity
Plant chemistry influences plant-nutritional quality, which in turn impacts plant-insect interactions. Plant secondary metabolites are pervasive in the plant kingdom and have been shown to influence both plant nutritional quality and plant-insect interactions. Levels of these secondary metabolites, as well as quantity, can impact availability of key macromolecules herbivorous insects need for optimal nutrient intake. Herbivorous insects can modulate their growth, rate of consumption, and frass production in response to diet with poor nutritional quality. Insects can also increase the production or activity of nutritional and detoxification enzymes to offset diet with poor nutritional quality. While the influence of plant secondary metabolites on nutrient intake is better understood in many plant systems, it is not well understood in plant-insect interactions involving Cannabis sativa. An increase in large-scale agricultural production of Cannabis has introduced a novel secondary metabolite, cannabinoids, a terpenophenolic compound with known physiological effects in many animal systems, onto the landscape. While insects have been shown to exhibit reduced performance on higher cannabinoid diets, insects lack human-analog cannabinoid receptors, so how these compounds interact with insect herbivores is not well understood. A goal of this study was to increase the understanding of how cannabinoids influence herbivorous insect performance.
To understand the influence of cannabinoids on insect performance and enzyme activity I performed no-choice feeding bioassays on fall armyworm (Spodoptera frugiperda) with artificial diet spiked with different concentrations of cannabidiol (CBD). I measured growth, consumption, and frass production. From these same larvae, I also analyzed detoxification and nutritional enzyme activities. I found that as CBD concentration increased in diet, growth and consumption of fall armyworm decreased. I also found that as CBD concentrations increased, protease and cytochrome P450 enzyme activity decreased, and β-glucosidase enzyme activity increased. These outcomes highlight potential mechanisms for both behavioral and biochemical mechanism by which CBD confers resistance to insect herbivores.
As agricultural production of Cannabis continues to increase, cannabinoids will continue to alter the chemical landscape of agricultural systems. How insect herbivores contend with cannabinoids is an important step in understanding plant-insect interactions in Cannabis systems. Identification of the structural and functional characteristics of protease and cytochrome P450 enzymes influenced by cannabinoids are possible future avenues of research that can better develop our understanding of Cannabis-insect interactions.