D3391: Insect herbivory has significant effects on cannabinoid and terpene levels in industrial hemp (Cannabis sativa)

Recently cultivation of industrial hemp (Cannabis sativa) is getting increasing attention due to its legalization in the 2018 farm bill. Despite this interest in hemp cultivation, there are significant risks associated which can result in economic losses to farmers. Hemp plants having levels of the cannabinoid tetrahydrocannabinol (THC) greater than 0.3%(w/w) are legally considered drugs, and farmers need to destroy these crops. Many plant species show an increase in specific secondary metabolites when exposed to biotic stresses like pests and pathogens. Infestation by biting-chewing insects could trigger biotic stress in hemp plants since herbivory activates the jasmonic acid signaling pathway that may lead to an increase in cannabinoid and terpene levels, two prominent groups of secondary metabolites produced in glandular trichomes of hemp. Thus, insect feeding on hemp may push THC levels above the legal limit. To test this hypothesis, we used different hemp varieties for methyl jasmonate treatments to mimic herbivory, and feeding assays with beet armyworm (Spodoptera exigua). While MeJA was applied up to three times and flower samples were collected 2 days after each application, armyworm larvae were allowed to feed for 2 days on hemp leaves and flowers sampled after 2 days. Flower samples were extracted, and cannabinoid and terpene contents quantified. Our analysis demonstrated that MeJA and herbivory result in altered terpene profiles and increased cannabinoid levels, suggesting that repeated/long-term herbivory can cause concerning THC levels. qRT-PCR analyses will reveal changes in the expression of genes in the terpene-cannabinoid biosynthetic network.