Hemp cannabinoids may have evolved to deter insect pests

The study opens the door for potentially developing pesticides from cannabinoid extracts, though such uses would be limited to non-edible plants, given the pharmacological properties of the compounds, which include CBD, THC and their precursor CBG.

In the decades since scientists first identified cannabinoids, research has focused on their medicinal and intoxicating effects, but it's never been clear why these plants evolved cannabinoids in the first place. Researchers have hypothesized that cannabinoids may protect plants from ultraviolet light, pathogens and herbivores.

"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," said Larry Smart, a plant breeder and professor in the School of Integrative Plant Sciences.

"But no one has put together a comprehensive set of experimental results to show a direct relationship between the accumulation of these cannabinoids and their harmful effects on insects," said Smart, senior author of the study.

"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," said George Stack, postdoctoral researcher in Smart's lab and the paper's first author.

In tests using hemp plants with varying concentrations of cannabinoids, the researchers discovered that damage from leaf-chewing insects (cabbage looper larvae) was higher in leaves with lower levels of cannabinoids.

"In the absence of cannabinoids, we saw heavy insect damage, and in the presence of cannabinoids, we saw much less damage," Smart said.

The Cornell program cannot work with high THC (the intoxicating compound found in marijuana) plants due to federal mandate, so THC as a pesticide was not tested in this research, Smart said.

More work is needed to understand how effective a cannabinoid derived pesticide might be in house plants.

"The potential use of cannabinoids as a pesticide is an exciting area for future research, but there will certainly be regulatory barriers due to pharmacological activity of the compounds, and more studies are needed to understand what pests cannabinoids will be effective against," Stack said.

The project was funded by the New York State Department of Agriculture and Markets through Empire State Development.