Plant-chomping insects can influence the level of cannabinoids in industrially grown hemp, researchers at the University of Maryland Eastern Shore have found. 
In lab conditions, the hemp-devouring appetite of the corn earworm — an insect dubbed “the number one hemp pest in North America” — significantly increased the level of cannabinoids in cannabidiol-rich (CBD) hemp varieties of Cherry Blossom and The Wife.
The latter variety, however, did not exhibit a change in natural levels of CBD and delta-9-tetrahydrocannabinol (D9-THC) levels when the experiment was replicated in the field, despite changes in Cherry Blossom having been measured.
Both the laboratory and on-the-field experiments of the study compared Cannabis sativa L. plants that were herbivore damaged (HD) with mechanically damaged (MD) and control plants. The latter two plants exhibited unchanged levels of CBD concentrations throughout all experiments.
In Cherry Blossom, the dry weight CBD percentage of HD, MD, and control plants was 17%, 6%, and 8%, respectively, in lab conditions. The levels of D9-THC in this variety were 1.2%, 0.33%, and 0.36%, respectively, for HD, MD, and control plants, also under lab conditions.
In The Wife, the CBD percentages consisted of 12%, 7%, and 6%, respectively, for HD, MD, and control plants under lab conditions whereas D9-THC levels were 0.93%, 0.26%, and 0.37%, respectively, for HD, MD and control plants.
The Maryland-based team of scientists further found that the larvae body masses of young corn earworms (Helicoverpa zea) significantly became smaller when fed on a CBD and D9-THC-spiked diet, compared to a control hemp diet.
The implications of the study for the greater industry are that herbivorous insect activity can cause spikes in plant cannabinoid production that exceed the 0.3% legal limit of D9-THC that defines hemp as hemp.
At the same time, the higher concentrations of CBD and D9-THC in herbivore-damaged cannabis plants might curb the growth, development, and spread of corn earworm larvae in the field.
Additional research is presently being carried out with different cannabis varieties with a focus on how biotic stressors — like herbivorous eating — impact the level of cannabinoids in the economically important plant.
Limited studies exist on interactions between hemp plants and insects due to the prior illegal status of the now industrially grown plant. The industry is still awaiting the development of an effective pest control product for optimal hemp production.
Reference Jackson B, Gilbert L, Tolosa T, Henry S, Volkis V, Zebelo S. The impact of insect herbivory in the level of cannabinoids in CBD hemp varieties. Research Square. 2021, https://doi.org/10.21203/rs.3.rs-155271/v1. [journal impact factor = N/A; times cited = 1]