Evaluating the impact of light quality on plant-herbivore interactions using hemp as the model system

Light-emitting diodes (LED) offer energy-efficient and customizable light sources that can be tailored to optimize plant chemistry and growth characteristics. Indoor cannabis production is the most energy-intensive crop in the United States and suffers from insect pest infestations including the cannabis aphid, Phorodon cannabis Passerini, which can negatively impact yield. Here we investigated the potential of light quality (color) to manage Cannabis sativa plant chemistry and cannabis aphids to increase crop quality. Cannabis was grown indoors under LED lighting systems where we manipulated the color spectrum. Within each light treatment, a subset of plants was exposed to aphid herbivory. Physical and chemical plant responses and aphid biology were measured. The interaction between light quality and herbivory drove the time to the first flower (cola) in our experimental plants. Light quality did not impact THC/CBD, but plants under increased blue light had higher bud yield than those grown under white light. The red-blue light treatment resulted in the tallest plants with the lowest leaf-stem dry mass and bud yield. Herbivory decreased bud yield and lowered the concentration of CBD/THC in buds. Lastly, light quality impacted the reproduction and mortality of the cannabis aphid. This study demonstrates the capacity of light quality to impact plant growth traits but offers no evidence for light quality impacting CBD/THC production in Cannabis. More importantly, herbivory resulting from aphid feeding was shown to decrease CBD and THC. Light quality impacted pest biology, supporting the potential use of light quality as a pest management tool.