Poor air quality is linked to stress in honey bees and can be compounded by the presence of disease

Authors: Mayack, Christopher; COOK, SARAH - University Of California, Davis; Nino, Bernardo; Drouville, Laura; Seshadri, Arathi; NINO, ELINA - University Of California, Davis

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/2/2023
Publication Date: 8/4/2023
Citation: Mayack, C.L., Cook, S.E., Nino, B.D., Drouville, L., Seshadri, A.H., Nino, E.L. 2023. Poor air quality is linked to stress in honey bees and can be compounded by the presence of disease. Insects. https://doi.org/10.3390/insects14080689.
DOI: https://doi.org/10.3390/insects14080689

Interpretive Summary: Climate change is associated with warmer and drier weather on average for central California. At the same time honey bees are being transported from all over the United States to central California for their pollination services as a way to increase yields for variety of crops, resulting in bees experiencing abiotic stressors. Higher temperatures can reduce air quality that can further exacerbate honey bee health challenges. We investigated the relationship between higher daily temperatures and poor air quality, and further demonstrated associations with incidences of pests (e.g. Varroa mites) and pathogens (e.g. Nosema ceranae). We also correlated the expression of genes linked to immune functioning, oxidative stress, and the buffering against temperature and air quality stressors. Higher temperatures are associated with poorer air quality and they are both associated with a lowering of immune system functions and an increase in the oxidative stress protection against bee pests and diseases. Varroa mites lower the ability of honey bees to buffer against temperature stress. Our study provides insights into interactions between climate change related abiotic stressors, and their relation to biotic stressors that underlie honey bee health declines.

Technical Abstract: Climate change related extreme weather events have manifested in the western United States as warmer and drier conditions with increased risk of wildfires. Honey bees, essential for crop pollination in California, are at the center of these extreme weather events. We associated maximum daily temperature and air quality index values with performance of colonies placed in wildfire prone areas and determined the impact of these abiotic stressors on gene expression and histologic traits. Our results indicate that poor air quality was associated with higher maximum daily temperatures and lower expression level of Prophenoloxidase gene, tied to immune system strength but higher expression level of Vitellogenin gene, tied to oxidative stress. There was a positive relationship between the prevalence of Varroa mites and N. ceranae pathogen and a negative correlation between Varroa mites and Heat Shock Protein 70 gene expression, suggesting the limited ability of mite-infested colonies to buffer against extreme temperatures. Histological analyses did not reveal overt signs of interaction between pathology and abiotic stressors, but N. ceranae infections were evident. Our study provides insights into interactions between abiotic stressors, their relation to common biotic stressors and to the expression of genes related to immunity and oxidative stress in bees.