Entomopathogenic Fungi Effectively Control Phorodon cannabis Aphid Population in Cannabis sativa Plants

The rapid expansion of the cannabis industry in Canada post-legalization has heightened the prevalence of pests, particularly the cannabis aphid <i>Phorodon cannabis</i> (<i>P. cannabis</i>), which poses significant threats to crop health. This study investigates the immediate effects of <i>P. cannabis</i> on <i>Cannabis sativa</i> (<i>C. sativa</i>) plants and explores biological control strategies utilizing entomopathogenic fungi. Fungal isolates of <i>Beauveria bassiana</i> and <i>Metarhizium anisopliae</i> were isolated from infected aphids, cultured, and characterized. Infection tests on aphids revealed that both fungi achieved 100% aphid mortality at high conidial concentrations (1 × 10⁷ conidia/mL) by the 10th DAT, with <i>Beauveria bassiana</i> demonstrating better efficacy. In greenhouse trials on three cannabis varieties, <i>B. bassiana</i> effectively controlled aphid populations, keeping levels low and stable in infested plants treated with <i>B. bassiana</i> at the concentration of 1 × 10⁷ conidia mL^-1 (I-B) and infested plants treated with insecticide (I-I). Both I-B and I-I treatments maintained aphid populations near zero for nine weeks. In contrast, control plants showed significant aphid growth, with the Perseid variety being the most susceptible, followed by Congo Durban, while GCC exhibited the lowest susceptibility. Cannabinoid and terpene analyses revealed that treatment with insecticide substantially decreased the amount of produced cannabinoids and terpenes. In contrast, <i>Beauveria bassiana</i>-treated plants exhibited higher concentrations of key metabolites, including delta-9-tetrahydrocannabinolic acid and cannabidiolic acid, and total terpenes, compared to chemically treated plants, and in two out of three cultivars, these concentrations were higher than in control, untreated plants. The findings highlight <i>Beauveria bassiana</i> as an eco-friendly alternative for pest management that not only controls aphids effectively but also supports the biochemical quality of cannabis plants.