Impact of nutritional stress on honey bee colony health

Authors: BRANCHICCELA, BELEN - Instituto Nacional De Investigacion Argropecuaria, Urugary; CASTELLI, LORELY - Instituto Nacional De Investigacion Argropecuaria, Urugary; Corona, Miguel; DIAZ-CETTI, SEBASTIAN - Instituto Nacional De Investigacion Argropecuaria, Urugary; INVERNIZZI, CIRO - Instituto Nacional De Investigacion Argropecuaria, Urugary; JORGE, DANIELA - Instituto Nacional De Investigacion Argropecuaria, Urugary; MENDOZA, YAMANDU - Instituto Nacional De Investigacion Argropecuaria, Urugary; SANTOS, ESTELA - Instituto Nacional De Investigacion Argropecuaria, Urugary; ZUNINO, PABLO - Instituto Nacional De Investigacion Argropecuaria, Urugary; ANTUNES, KARINA - Instituto Nacional De Investigacion Argropecuaria, Urugary

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/20/2019
Publication Date: 7/12/2019
Citation: Branchiccela, B., Castelli, L., Corona, M.V., Diaz-Cetti, S., Invernizzi, C., Jorge, D., Mendoza, Y., Santos, E., Zunino, P., Antunes, K. 2019. Impact of nutritional stress on honey bee colony health. Scientific Reports. 9(1):10156. https://doi.org/10.1038/s41598-019-46453-9.
DOI: https://doi.org/10.1038/s41598-019-46453-9

Interpretive Summary: Honey bee colony losses have increased worldwide during recent years. Several lines of evidence indicate that nutritional stress, especially a reduction of pollen diversity and amount due to the increased use of monocultures, is an important contributing factor associated with declines in honeybee populations. Although it has been hypothesized that nutritional stress leads to colony collapse, there are few studies performed under field conditions investigating the relationships among pollen quality, susceptibility to pathogens and long term effects on colony strength and survival. In this study, we aimed to test the effects of monofloral and polyfloral pollen diets at the colony level on pathogen levels and their long-term effects on colony fitness. In order to accomplish this objective, we took advantage of a natural landscape composed of a monoculture of Eucalyptus grandis trees in Uruguay. A first set of colonies (Monofloral diet) was placed at this landscape to form an experimental group of colonies fed with a monofloral pollen diet. A second experimental group (Polyfloral diet) was created by supplementing colonies with a patty composed by polyfloral pollen previously collected from other locations with diverse plant species. Our results showed that a poor nutritional quality monofloral pollen diet was associated with higher levels of one of the most prevalent pathogens in Uruguay, the microsporidian Nosema spp, during the flowering period of Eucalyptus grandis at autumn. Analyses performed next spring, on the same colonies, revealed long-term effects of colony nutrition on colony strength. The results of this study confirm that nutritional stress caused by monofloral pollen diets has a negative effect on colonies’ susceptibility to Nosema spp and that this nutritional stress has a long-term effect on colonies’ fitness.

Technical Abstract: During the past decade, high rates of honey bee colony losses have been reported worldwide. Among the factors associated with these losses is tnutritional stress due to habitat depletion, which can increase the vulnerability of honey bees to the infection of the different pest and pathogens. We hypothesize that nutritional stress affects the sanitary status of the colonies, promoting colony depopulation and colony losses. The aim of this study was, under field conditions, to analyze the effect of nutritional stress in colonies' strength, mortality and in the infection level of the most important pathogens that affects bees. Two groups of colonies were set in an Eucalyptus grandis plantation at the beginning of the flowering period (groups M and P). This environment is a natural scenario where nutritional and sanitary problems converge since pollen of these trees is nutritionally poor and colonies are notably infected with Nosema spp. Both groups of colonies had environmental pollen available and colonies from group P were supplemented with a polyfloral pollen patty during the flowering period (autumn). Infection level of Nosema spp, RNA virus and Varroa destructor, as well as the prevalence of Lotmaria passim was analyzed. We also estimated colonies' strength during the E. grandis flowering period and in the next spring, to evaluate the long-term effect. Our results proved under field conditions, that nutritional stress affects the infections with N. ceranae, having consequences in colony depopulation. In addition, the consequences of nutritional stress had long-term effects on colonies´ strength.