Effects of insect herbivory on the terpene and cannabinoid profiles in industrial hemp (Cannabis sativa) and potential biological functions

Cultivation of industrial hemp (Cannabis sativa) is getting increasing attention due to its legalization in the 2018 farm bill. However, there are significant economic risks associated with hemp cultivation since plants having levels of the cannabinoid tetrahydrocannabinol (THC) greater than 0.3 % are legally considered drugs and need to be destroyed. Many plant species show an increase in specific specialized metabolites when exposed to biotic stresses such as insect herbivory. Infestation by biting-chewing insects will trigger biotic stress in hemp plants and through the jasmonic acid signaling pathway may lead to an increase in terpene and cannabinoid levels, two prominent groups of specialized metabolites produced in glandular trichomes of hemp. Thus, insect herbivory on hemp may push THC levels above the legal limit. To test this hypothesis, we used hemp varieties for methyl jasmonate treatments to mimic herbivory and feeding assays with beet armyworm (Spodoptera exigua). Flower samples were extracted, and terpene and cannabinoid profiles analyzed by GC/MS and LC/MS. Our analysis demonstrated that both MeJA and insect herbivory resulted in quantitative and qualitative changes in the terpene and cannabinoid profiles, thus suggesting that repeated herbivory can cause concerning THC levels. While THC likely has no psychoactive effect on insects due to their lack of respective cannabinoid receptors, little is known about how behavior and performance of insects is affected by cannabinoids including those accumulating to significant amounts upon herbivory. To study potential effects, we are performing beet armyworm feeding assays with a set of selected cannabinoid compounds.