The research reveals a direct relationship between higher concentrations of cannabinoids in hemp leaves and reduced damage from insect larvae, suggesting these compounds might have evolved as a defense mechanism against pests.
“In the decades since the first cannabinoids were identified by scientists, research has focused almost exclusively on the function and capacity of cannabinoids as medicines and intoxicants for humans and other vertebrates,” wrote the study authors.
“Very little is known about the adaptive value of cannabinoid production, though several hypotheses have been proposed including protection from ultraviolet radiation, pathogens, and herbivores.”
Larry Smart is a professor in the School of Integrative Plant Sciences at Cornell and the senior author of the study.
“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 Professor Smart.
“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.”
Study first author George Stack, a postdoctoral researcher in Smart’s lab, said the research provides 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 researchers tested the efficacy of hemp plants with varying concentrations of cannabinoids. Smart said the team saw heavy insect damage in the absence of cannabinoids, and much less damage in the presence of cannabinoids.
“In the field, foliar cannabinoid concentration was inversely correlated with chewing herbivore damage,” wrote the researchers.
“On detached leaves, Trichoplusia ni larvae consumed less leaf area and grew less when feeding on leaves with greater concentrations of cannabinoids.”
The Cornell program cannot work with high THC plants due to federal mandate, so THC was not tested as a pesticide in this research, noted Smart.
Further research is needed to understand how effective cannabinoid-based pesticides may be for use on 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,” explained Stack.
The research was funded by the New York State Department of Agriculture and Markets through Empire State Development.
The study is published in the journal Horticulture Research.
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