In the United States, industrial hemp is defined as a Cannabis sativa L. plant not containing more than 0.3% delta-9-tetrahydrocannabinol (D9THC) by dry weight. Plants respond to insect herbivore damage by changing their chemistry to counter the effects of herbivore attack. Here, we hypothesized that the corn earworm (Helicoverpa zea) infestation might impact the level of cannabinoids (Cannabidiol (CBD) and D9THC).
In a laboratory trial, the CBD hemp, Cherry Blossom, and The Wife varieties were subjected to herbivore damage (HD), Mechanical damage (MD), and Control. After 24hrs of the treatments, we found a significant increase in CBD and D9THC in HD plants compared with MD and Control plants. Similar experiments were conducted in the field condition. A substantial increase in CBD and D9THC observed in herbivore damaged hemp plants compared to the control plants. However, in the field trial, the levels of cannabinoids were not significantly higher in The wife variety. Interestingly, the Corn earworm larvae fed with CBD and D9THC spiked diet showed a significant reduction in body mass, as compared to the larvae fed with the control diets.
The level of cannabinoids seems not genetically fixed somewhat; it is affected by insect herbivory. Our results suggest that CBD hemp plants are exposed to insect herbivory spikes in cannabinoid production and surpass the 0.3 % legal limit of D9THC. The growth and development of Corn earworm, the number one hemp pest in North America affected by cannabinoids. The increased concentration of CBD and D9THC observed in herbivore damaged hemp plants might be associated with the direct deterrence of the corn earworm larvae. Further research underway using different hemp varieties to assess if herbivory and other biotic stressors impact the level of cannabinoids.