Extracts of Polypore Mushroom Mycelia Reduce Viruses in Honey Bees

Abstract

Waves of highly infectious viruses sweeping through global honey bee populations have contributed to recent declines in honey bee health. Bees have been observed foraging on mushroom mycelium, suggesting that they may be deriving medicinal or nutritional value from fungi. Fungi are known to produce a wide array of chemicals with antimicrobial activity, including compounds active against bacteria, other fungi, or viruses. We tested extracts from the mycelium of multiple polypore fungal species known to have antiviral properties. Extracts from amadou (Fomes) and reishi (Ganoderma) fungi reduced the levels of honey bee deformed wing virus (DWV) and Lake Sinai virus (LSV) in a dose-dependent manner. In field trials, colonies fed Ganoderma resinaceum extract exhibited a 79-fold reduction in DWV and a 45,000-fold reduction in LSV compared to control colonies. These findings indicate honey bees may gain health benefits from fungi and their antimicrobial compounds.

Figure 1

Extracts from fungi reduced deformed wing virus (DWV) in honey bees. (A) DWV shortens the lifespan of workers and causes developmental abnormalities in honey bees including deformed wings. (B) Honey bees forage on fungal mycelium where they ingest liquid exudates. (C) Bees fed extracts from polypore mycelium exhibited lower DWV virus titers. In three different trials, mixing fungal extracts into caged bees’ sucrose syrup food significantly reduced the levels of DWV as assayed by qPCR. Notably, the extracts of F. fomentarius mycelium reduced DWV more than 800-fold in the first trial (2-tailed t-test, n = 10, t = 1.12, p = 0.005). For each trial, qPCR ΔCt values are normalized to mean value of the respective control groups. Photos: Xolani90-https://commons.wikimedia.org/wiki/File:Deformed_Wing_Virus_in_worker_bee.JPG - [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]-no changes (A), PES (B, Fomes, G. resinaceum), Titus Tscharntke – Wikimedia Commons (Betula), George Chernilevsky-Wikimedia Commons (G. applanatum), Norbert Nagel -https://commons.wikimedia.org/wiki/File:Trametes_versicolor_-_Coriolus_versicolor_-_Polyporus_versicolor_-_Schmetterlingstramete_-_Bunte_Tramete_-_Schmetterlingsporling_-_01.jpg [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]-cropped (Trametes).

Figure 2

Lake Sinai virus (LSV) is reduced by fungal extract treatments. (A) All 36 individual bee abdomens from our source population tested positive for both DWV and LSV. LSV was more highly expressed than DWV, and more highly expressed than the honey bee RpS5 reference gene. (B) Fungal extracts reduced LSV titers in bees after 7 days of treatment. F. fomentarius significantly reduced LSV at a 1% dosage (2-tailed t-test, n = 8, t = 3.96, p = 0.009, ΔΔCt fold change = 5.40). The greatest fold change difference was seen with G. resinaceum extract where treatment reduced LSV levels in bees 499-fold compared to bees fed only sucrose syrup (2-tailed t-test, n = 8, t = 2.59, p = 0.084).

Figure 3

Fungal extracts reduce DWV and LSV levels in field trials. (A) Fungal extracts were mixed into sucrose solution and fed to bees using in-hive feeders commonly used in beekeeping. (B) Both Fomes and Ganoderma extracts significantly reduced DWV and LSV levels in field trials using 5-frame colonies with bees divided from a common population. Bees were sampled for virus levels at the start of treatment and 12 days later. Colonies fed G. resinaceum extracts exhibited a 79-fold greater reduction in DWV and a 45,000-fold greater reduction in LSV compared to controls fed sugar syrup. Quantitative PCR ΔCt values are normalized to the mean starting virus levels across all groups. Photo: WSS.