Ecological Perspectives on Cannabis sativa Phytochemistry: Biotic Interactions and Abiotic Stress in Managed and Natural Systems
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Authors
Kay, Ericka Rochelle
Issue Date
2025
Type
Dissertation
Language
en_US
Keywords
Cannabis sativa , Phytochemistry , plant-insect interactions
Alternative Title
Abstract
Cannabis sativa is a chemically diverse and ecologically significant plant whose re-cent expansion across North American landscapes offers a unique opportunity to investi-gate the ecological roles of phytochemical diversity. While much attention has been given to cannabinoids for their commercial value, relatively little is known about how variation in phytochemistry influences arthropod interactions, or how these interactions differ across environmental conditions and cultivation systems. This dissertation takes an ecological lens to Cannabis phytochemistry, combining observational surveys, comparative analyses, and field experiments to explore how chemical traits structure arthropod communities across both natural and human-shaped systems. One of the first steps toward understanding any plant-insect system is to characterize the arthropod community. To answer this, I surveyed arthropods across 29 Cannabis sites in five western U.S. states, encompassing feral hemp, CBD- dominant hemp, and THC- dominant marijuana grown under diverse conditions. These field surveys—spanning backyard gardens, research plots, and large-scale farms—revealed rich and variable arthropod communities. A total of 5,817 arthropods representing 194 morphospecies from 13 insect orders were collected. Hemiptera, particularly aphids in the genus Phorodon, dominated in both abundance and site occupancy and were the most consistent insect associates across chemotypes and regions. Cultivated hemp supported the highest morphospecies richness, followed by cultivated marijuana and feral hemp. Most morphospecies occurred in only one location or chemotype–region combination, indicating high spatial turnover and little evidence for a core Cannabis-associated insect community. However, a few predators such as Orius sp. were broadly distributed and frequently co-occurred with aphids, suggesting potential roles in natural biological control.Building on these patterns, I turned to the role of selection. In Nebraska, where feral hemp has persisted in ditches and field margins over centuries, I compared six pairs of cul-tivated and feral Cannabis populations to assess how natural and artificial selection influ-ence plant chemistry and ecological dynamics. Cultivated plants—selected for high canna-binoid production—had greater cannabinoid diversity but reduced terpene diversity com-pared to their feral counterparts. These chemical shifts had ecological consequences: in cul-tivated fields, higher phytochemical diversity was associated with lower herbivore abun-dance, while in feral sites, this relationship was weaker. Natural enemies tracked herbivores in both systems, but predator-prey dynamics were stronger in feral fields. These findings suggest that selection for cannabinoid yield may weaken terpene-based defenses, altering not only the chemical phenotype of the plant but also its ecological relationships.
To disentangle the effects of environment from selection history, I conducted a fully factorial field experiment exposing clonal hemp plants to three water treatments over three growing seasons. Abiotic stressors altered both plant form and function: stressed plants were shorter, had reduced phytochemical diversity, and supported fewer arthropods. Can-nabidiol concentration was positively associated with arthropod richness, while high overall phytochemical diversity—particularly under stress—tended to suppress herbivore abun-dance. These results suggest that phytochemical diversity can serve multiple, and some-times opposing, ecological functions depending on context, and that environmental stress reshapes the ecological phenotype of Cannabis in ways that are not easily predicted by chemistry alone.
Across all three projects, a unifying pattern emerged: phytochemical composition plays a central role in shaping insect communities, but its effects are complex, context-dependent, and shaped by both human intention and environmental forces. Together, these findings offer new ecological perspectives on a plant that is both ancient and newly rele-vant, and demonstrate the value of blending natural history, field ecology, and metabolomics to understand how chemical traits mediate biotic interactions in emerging agroecosystems.