Assessing the adaptive role of cannabidiol (CBD) in Cannabis sativa defense against Cannabis aphids

Authors: MACWILLIAMS, JACOB - Colorado State University; Peirce, Erika; PITT, WILLIAM - Colorado State University; SCHREINER, MELISSA - Colorado State University; MATTHEWS, TIERRA - Colorado State University; YAO, LINXING - Colorado State University; BROECKLING, COREY - Colorado State University; NACHAPPA, PUNYA - Colorado State University

Submitted to: Frontiers in Ecology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/8/2023
Publication Date: N/A
Citation: N/A

Interpretive Summary: Plants have special chemicals that protect them from insects that eat them. These chemicals can be harmful or unappetizing to insects. We know a lot about how this works for some plants, like wheat and corn, but we need to learn more about how it works for other plants, like hemp. Hemp is a plant that produces chemicals called cannabinoids (like cannabidol, CBD) that are not found in many other plants. In this study, we wanted to find out if CBD, one of the main cannabinoids in hemp, helps the plant protect itself from cannabis aphids (Phorodon cannabis), which are insects that can damage hemp. We found that aphids had a harder time reproducing and lived shorter lives when they ate the high-CBD versus the low-CBD hemp. But they reproduced more when we gave the aphids extra CBD in an artificial diet. Interestingly, the aphids did not seem to affect the levels of most cannabinoids in the plant, except for tetrahydrocannabinol (THC). This suggests that other chemicals in the plant might make it harder for the aphids to survive. We also found that when the aphids fed on the plant, it caused changes in the plant's hormones, which are like chemical messengers in the body. Overall, this study helps us understand more about how plants and insects communicate chemically and how we can use this knowledge to protect crops in the future.

Technical Abstract: Plants protect themselves from insect herbivores with a multitude of specialized or secondary metabolites which have toxic, repellent, and/or anti-nutritional effects on the feeding herbivores. Most of our knowledge of plant-insect interactions has been gleaned from model species such as Arabidopsis and other staple crops. For less studied crops such as hemp (Cannabis sativa, <0.3% tetrahydrocannabinol, '9-THC), there is no information on plant responses to herbivores. Cannabis sativa is known for having evolved unique, specialized metabolites known as cannabinoids, which include '9-THC and cannabidiol (CBD) and more than 90 other cannabinoids. However, despite the assumption that cannabinoids evolved as novel herbivory defense adaptations, there is limited research addressing the role of cannabinoids in C. sativa responses to insect herbivores. Here we investigated the role of CBD, the predominant cannabinoid in hemp, in plant defense against cannabis aphid (Phorodon cannabis), one of the most damaging pests of hemp. We found that mean fecundity, net reproductive rate (R0) and adult longevity of cannabis aphids was reduced on the high cannabinoid cultivar compared to the low- cannabinoid cultivar. In contrast, supplementation of CBD in artificial feeding assays increased aphid fecundity from day 1 to day 3. Additionally, aphid feeding did not impact cannabinoid levels in leaf tissues with the exception of '9-THC. This suggests that other cannabinoids and/or metabolites such as terpenes are causing the observed decrease in aphid performance on the high-cannabinoid cultivar. Cannabis aphid feeding significantly increased levels of all major phytohormones, salicylic acid, jasmonic acid, and abscisic acid. These results provide new insights into plant-insect chemical communication and coevolution and can aid in developing new approaches to sustainable pest management.