How Cannabinoids in Hemp Plants Evolved as Natural Defenses Against Pests?

Researchers at Cornell University have unveiled a groundbreaking study suggesting that cannabinoids, the naturally occurring compounds found in hemp plants, may have evolved as a defense mechanism against pest infestation. The research, led by Larry Smart, a plant breeder and professor in the School of Integrative Plant Sciences, found a direct correlation between higher concentrations of cannabinoids in hemp leaves and reduced damage from insect larvae.

While cannabinoids, such as CBD, THC, and CBG, have been extensively studied for their medicinal and psychoactive effects, the evolutionary purpose behind their presence in plants has remained unclear. Previous hypotheses suggested that cannabinoids might serve as protection against ultraviolet light, pathogens, and herbivores.

Smart emphasized the significance of the study, stating, "It has been speculated that they are defensive compounds, because they primarily accumulate in female flowers to protect seeds, which is a fairly common concept in plants." However, until now, no comprehensive set of experimental results had demonstrated a direct relationship between cannabinoid accumulation and their deterrent effects on insects.

George Stack, a postdoctoral researcher in Smart's lab and the first author of the paper, highlighted the potential implications of the findings. "The study gives us insight into how cannabinoids function in natural systems and can help us develop new THC-compliant hemp cultivars that maintain these natural built-in defenses against herbivores."

The research involved tests on hemp plants with varying cannabinoid concentrations, revealing that leaves with lower cannabinoid levels experienced higher damage from leaf-chewing insects, specifically cabbage looper larvae. Smart noted, "In the absence of cannabinoids, we saw heavy insect damage, and in the presence of cannabinoids, we saw much less damage."

Despite the potential for developing pesticides from cannabinoid extracts, the use of such compounds as pesticides would be limited to non-edible plants due to the pharmacological properties of cannabinoids. The study did not test THC, the intoxicating compound found in marijuana, as a pesticide, as the Cornell program cannot work with high-THC plants based on federal mandates.

While the prospect of cannabinoid-derived pesticides is exciting, Stack acknowledged that regulatory barriers exist due to the pharmacological activity of the compounds. Further research is required to determine the effectiveness of cannabinoid-based pesticides and to identify the specific pests they may target.

The paper, titled "Cannabinoids function in defense against chewing herbivores in Cannabis sativa L.," was published in Horticulture Research in 2023.

Journal Reference:

1. George M Stack, Stephen I Snyder, Jacob A Toth, Michael A Quade, Jamie L Crawford, John K McKay, John Nicholas Jackowetz, Ping Wang, Glenn Philippe, Julie L Hansen, Virginia M Moore, Jocelyn K C Rose, Lawrence B Smart. Cannabinoids function in defense against chewing herbivores in Cannabis sativa L.. Horticulture Research, 2023; DOI: 10.1093/hr/uhad207
2. Cornell University. "Hemp cannabinoids may have evolved to deter insect pests." ScienceDaily. ScienceDaily, 15 November 2023. <www.sciencedaily.com/releases/2023/11/231115133230.htm>.

3. Story Source: Materials provided by Cornell University. Original written by Krishna Ramanujan, Cornell Chronicle. Note: Content may be edited for style and length.