The type of honey consumed influences bees’ tolerance to pesticides

Insecticide toxicity to plant-feeding pest insects has long been known to vary with the host plant. This phenomenon has been widely documented in both leaf-feeding and sap-feeding insects.

The species-specific phytochemical composition of host-plant tissues is thought to determine the induction of insect enzymes that metabolise and detoxify insecticides. However, individual phytochemicals have rarely been linked to host-plant-associated variation in pesticide toxicity. No studies to date had examined how nectar source and honey phytochemical composition affect insecticide toxicity to pollinators.

In this study, we compared LD50 values for bifenthrin, an insecticide frequently contaminating nectar and pollen in agroecosystems, in western honey bees, Apis mellifera, fed three phytochemically different monofloral honeys: Nyssa ogeche (tupelo), Robinia pseudoacacia (black locust, commonly called acacia) and Fagopyrum esculentum (buckwheat). Bifenthrin LD50 values varied with the honey diet and were associated with its species-specific phytochemical content. Buckwheat and black locust honeys had richer phenolic acid and flavonoid profiles than tupelo honey. Buckwheat honey had the highest total phytochemical content and was associated with the highest bifenthrin LD50, meaning the lowest toxicity.

Although enhanced xenobiotic detoxification in honey bees in response to the honey consumed probably evolved in response to potentially toxic phytochemicals, detoxification induced by phytochemical-rich honeys is likely beneficial in pesticide-contaminated environments. Honey also contains phytochemicals that do not originate from floral nectar (Nešović et al. 2020).

As Soler et al. (1995) reported, honey contains not only nectar-derived phytochemicals but also characteristic propolis and/or beeswax flavonoids: chrysin, galangin, tectochrysin, pinocembrin and pinobanksin. In our study, these were positively correlated with increased insecticide tolerance. The phenolic acid p-coumaric acid is a common constituent of European propolis (Hegazi et al. 2000) and is present in honey.

Propolis-derived flavonoids, including pinocembrin, pinobanksin and galangin, were absent or present at very low concentrations in our tupelo honey samples compared with black locust and buckwheat honey. Buckwheat honey was particularly rich in them. Mao et al. (2013) reported that p-coumaric acid was the strongest inducer of the detoxification enzyme CYP9Q3 among the phenolic acids and flavonoids tested, while chrysin and naringenin induced CYP9Q3 more effectively than pinocembrin and galangin.

In conclusion, honey—the principal stored food during a substantial part of the bee life cycle—probably has greater importance for bee health than previously recognised, especially if bees can self-regulate detoxification enzyme induction, as they apparently do through self-medication in the presence of pathogens (Gherman et al. 2014; Spivak et al. 2019; Tihelka 2018).

Adapted from: Variation in Pesticide Toxicity in the Western Honey Bee (Apis mellifera) Associated with Consuming Phytochemically Different Monofloral Honeys — Ling-Hsiu Liao et al., Journal of Chemical Ecology https://doi.org/10.1007/s10886-024-01495-w