"Despite the assumption that cannabinoids evolved as novel herbivory defense adaptations, there is limited research addressing the role of cannabinoids in the cannabis plant's responses to insect herbivores." Therefore, researchers from Colorado State University investigated the role of cannabidiol (CBD) in plant defense against cannabis aphids, one of the most damaging pests of cannabis.
Impact on aphid performance
To investigate the impact of cannabinoids on aphid performance, a high-cannabinoid cultivar (Unicorn) and a low-cannabinoid cultivar (Tiborszallasi) were used in life history studies. Cannabis aphid life history traits were reduced on the high-cannabinoid cultivar compared to the low-cannabinoid cultivar.
"Though the presence of cannabinoids had a detrimental effect on cannabis aphid performance, development time showed the opposite trend," the researchers explain. "Cannabis aphids had a shorter development time on the high-cannabinoid cultivar compared to the low-cannabinoid cultivar. Cannabis aphids showed a delayed preference towards low-cannabinoid over high-cannabinoid cultivar leaf tissues in choice assays at 72-hour post-release."
Interestingly, when cannabis aphids were fed an artificial diet supplemented with DMSO + 1 mM CBD, aphid populations increased relative to diet alone (baseline) and DMSO alone from day one until day 3, the research shows. "This suggests that CBD supplementation in artificial feeding assays does not have a negative impact on cannabis aphids that have been observed with other hemp pests like tobacco hornworm and fall armyworm."
Effect on cannabinoid levels
"Overall, there was minimal effect of aphid infestation on cannabinoid levels. But we did detect increased THC levels in response to aphid infestation in the high-cannabinoid cultivar," the researchers say. "Other studies have found that arthropod feeding can alter cannabinoid levels. For example, spider mites' infestation led to increased CBD and THC levels, whereas tobacco hornworm infestation led to a decrease in CBD. This suggests that cannabis' defense responses are not conserved against herbivores and likely depends on the type (feeding guild) and level (short term vs long term) of stress and interaction with other environmental factors, including abiotic factors."
Developing effective pest management
"The other predominant metabolite in cannabis is terpenes, which could be contributing to the reduced aphid performance on the high-cannabinoid cultivar. Indeed, there are over 100 known terpenes in cannabis, and many are known to act as natural insecticides. Also, cannabis is covered by dense trichomes that may act as a physical barrier to movement and/or secrete specialized metabolites that have anti-herbivory effects. Understanding the impact of cannabis' physical and chemical defenses can aid in the development of effective and sustainable pest management program in this new crop," the researchers conclude.
To read the complete research, go to ncbi.nlm.nih.gov
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