COS 79-1 - Bumble bee pharmacies in your garden: Medicinal effects of cultivated basil (Ocimum basilicum) on a bumble bee parasite

Background/Question/Methods

When infected by parasites, some animals may “self-medicate” and change their diets to consume plant material that improves survival or fitness. While there is currently scant evidence that bumble bees (Bombus spp.) engage in self-medicating behavior, many phytochemicals found in wild and cultivated flowers are bioactive against bumble bee parasites. Here, we evaluate the medicinal effects of cultivated basil (Ocimum basilicum) on common eastern bumble bees (Bombus impatiens) infected with the trypanosome endoparasite Crithidia bombi. We planted six varieties of basil in enclosed plots and released Crithidia-infected bumble bees to forage exclusively in these plots for one week. We also collected volatile organic compounds (VOCs) produced by basil flowers and used gas chromatography-mass spectrometry to characterize and quantify scent data. Like many cultivated herbs, basil varieties are bred for distinct scents and flavors, resulting in unique chemical profiles produced by each variety. Such chemical profile variation may result in differential effects of basil varieties on Crithidia. To ascertain which chemicals, if any, are responsible for a medicinal effect of a basil variety, we analyzed VOC data to identify chemical profile similarities.

Results/Conclusions

We collected 260 bees across 28 enclosed plots. We observed three “low-parasite” basil varieties – bees that foraged on these varieties had significantly lower parasite counts than those that foraged on other varieties. Between all three “low-parasite” varieties, we found several compounds that have previously been shown to improve Crithidia infections when consumed by bees. These compounds are also produced by basil relatives in the mint family Lamiaceae, including native North American plants used in pollinator habitats such as bee balm (Monarda spp.). We hope to use these findings to encourage gardeners and farmers to plant medicinal Lamiaceae on their lands, including medicinal varieties of basil.