Toxic and repellent effects of hemp leaf extracts and cannabidiol against adult female yellow fever mosquitoes, Aedes aegypti.

Hemp (Cannabis sativa) derived products have emerged as potential sources of novel biopesticides. We recently demonstrated that a hemp leaf extract was toxic to larvae of the yellow fever mosquito Aedes aegypti, and that cannabidiol (CBD) was the primary larvicidal component of the extract. Here we evaluated the toxic and repellent effects of a hemp leaf extract and CBD against adult female Ae. aegypti. Toxicity was assessed using an acute topical assay in which mosquitoes received a 500 nL application to the thorax and mortality was recorded at 24 h. Repellency was then evaluated using two complementary bioassays: (i) a no-choice membrane blood-feeding assay to quantify feeding deterrence, and (ii) a mosquito airborne repellency test (MART) to assess spatial repellency. Topical application of CBD-rich hemp leaf extract induced dose-dependent mortality in adult Ae. aegypti with a LD50 of 22.13 µg/mosquito at 24 h. When CBD isolate was tested at its equivalent doses in the extract, it caused significantly lower mortality than the hemp extract. In the membrane blood-feeding repellency assay, the hemp leaf extract repelled mosquitoes in a dose-dependent manner, whereas CBD produced weaker effects even at higher equivalent doses. In the MART assay, the hemp extract did not elicit spatial repellency, suggesting low volatility of the repellent compounds. Taken together, our results demonstrate that CBD does not fully explain the adulticidal or repellent effects of the CBD-rich hemp leaf extract against adult female Ae. aegypti suggesting that other compounds contribute to the bioactivity of hemp leaf extracts against adult female mosquitoes.