Do diet and Fumagillin treatment impact Vairimorpha (Nosema) spp. (Microspora: Nosematidae) infections in honey bees (Hymenoptera: Apidae) and improve survival and growth of colonies overwintered in cold storage?

Authors: Hoffman, Gloria; Corby-Harris, Vanessa; GRAHAN, H. - Retired ARS Employee; Chambers, Mona; Watkins De Jong, Emily; Snyder, Lucy

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/5/2024
Publication Date: 9/28/2024
Citation: Hoffman, G.D., Corby-Harris, V.L., Grahan, H., Chambers, M.L., Watkins De Jong, E.E., Snyder, L.A. 2024. Do diet and Fumagillin treatment impact Vairimorpha (Nosema) spp. (Microspora: Nosematidae) infections in honey bees (Hymenoptera: Apidae) and improve survival and growth of colonies overwintered in cold storage?. Journal of Economic Entomology. 117(6);2203-2218. https://doi.org/10.1093/jee/toae187.
DOI: https://doi.org/10.1093/jee/toae187

Interpretive Summary: Vairimorpha (Nosema) spp. is a spore forming microsporidian that proliferates in the midgut of honey bees. Nosema can impact colony growth and survival particularly over the winter when bees are confined in the hive. Fumagillin treatments can reduce infections, but whether it improves overwintering colony survival is not clear. Diet also can affect the severity of Nosema infections. We conducted a 2-year study to determine the effects of Nosema on the size and survival of colonies overwintered in cold storage. In Year-1, no treatments were applied to colonies prior to cold storage overwintering. Colony survival and sizes after cold storage and almond bloom were comparable between groups with high and low pre-cold storage Nosema infections. In Year-2, size and survival were compared among colonies with and without Fumagillin treatment that were fed either pollen or a commercial protein supplement prior to overwintering. Colonies treated with Fumagillin had lower spore numbers than untreated, but colony sizes after cold storage and almond bloom were similar among the treatments. However, more untreated colonies with zero spores per bee could be rented for almond pollination and were alive after bloom than those averaging more than 1 million spores per bee. Fat body composition in bees can affect overwintering success. In both years, fat body weights and protein concentrations increased, and lipid concentrations decreased in all treatment groups while bees were in cold storage. Diet and Nosema infections did not affect fat body metrics. However, Fumagillin treatments negatively affected pre-cold storage fat body protein concentrations and colony sizes after cold storage and almond bloom. Treating Nosema before overwintering in cold storage might result in greater colony survival if spore numbers are high but undetectable or even negative effects can occur especially if spore numbers are low.

Technical Abstract: Vairimorpha (Microsporidia: Nosematidae) is a microsporidian that infects honey bees especially in winter. Fumagillin can reduce infections, but whether overwintering survival is improved is unclear. The diet also may influence the severity of Nosema infections. We examined the relationship between Nosema and colony size and survival in hives overwintered in cold storage facilities. In year 1, no Fumagillin treatments were applied. Colony size and survival after cold storage and almond bloom were comparable between groups with high and low pre-cold storage infections. In year 2, size and survival were compared among colonies with and without Fumagillin treatment that were fed either pollen or protein supplement prior to overwintering. Colonies treated with Fumagillin had lower spore numbers than untreated, but colony sizes and survival were similar among the treatments. However, more colonies with zero spores per bee could be rented for almond pollination and were alive after bloom than those averaging >1 million spores per bee. Fat body metrics can affect overwintering success. In both years, fat body weights and protein concentrations increased, and lipid concentrations decreased while bees were in cold storage. Fat body metrics did not differ with Nosema infection levels. However, Fumagillin negatively affected pre-cold storage fat body protein concentrations and colony sizes after cold storage and almond bloom. Treating with Fumagillin before overwintering in cold storage might result in greater colony survival if spore numbers are high, but undetectable or even negative effects when spore numbers are low.