Cannabinoid-producing plant (left) with very little insect damage adjacent to cannabinoid-free plant (right) that has been completely defoliated by insects. Credit: George Stack
A recent study from Cornell AgriTech in the College of Agriculture and Life Sciences (CALS) may contain the answer as to why hemp plants have evolved to contain cannabinoids. Despite decades of research into cannabinoid's medicinal and intoxicating properties, little research has been conducted to demonstrate what function they serve within the plant.
In the past researchers have theorized that cannabinoids could serve functions such as protecting the plants from UV light, pathogens, or 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 professor in the School of Integrative Plant Science at Cornell AgriTech. "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."
Started in 2017, the Cornell hemp breeding program has been working to evaluate a multitude of commercially available hemp cultivars to determine which were best suited for local environmental conditions. During evaluation, a cultivar from Ukraine was noted as being particularly susceptible to Japanese beetles while the other cultivars were not.
"At the end of the season, as we characterized the chemistry of those plants, we learned that the plants from the Ukrainian program did not make any cannabinoids," Smart said. In the study, published in Horticulture Research, the researchers observed a direct correlation between cannabinoid concentration and a reduction in predation from leaf-chewing insects.
"In the absence of cannabinoids, we saw heavy insect damage, and in the presence of cannabinoids, we saw much less damage," Smart said. In further testing, CBDA and CBGA were isolated and applied to artificial insect diets in varying concentrations. Further observations revealed that insect larvae growth and survival rates were lower as cannabinoid concentration increased.
"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," said George Stack, a postdoctoral researcher in Smart's lab.