Hot and sour: parasite adaptations to honey bee body temperature and pH

Authors: PALMER-YOUNG, EVAN - Orise Fellow; RAFFEL, THOMAS - Oakland University; Evans, Jay

Submitted to: Proceedings of the Royal Society. B. Biological Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/28/2021
Publication Date: 12/1/2021
Citation: Palmer-Young, E., Raffel, T., Evans, J.D. 2021. Hot and sour: parasite adaptations to honey bee body temperature and pH. Proceedings of the Royal Society B. 228(1964):1-10. https://doi.org/10.1098/rspb.2021.1517.
DOI: https://doi.org/10.1098/rspb.2021.1517

Interpretive Summary: Honey bee colonies are at risk for numerous diseases, jeopardizing their immense role in crop pollination. Gut parasites can limit colony growth and impact over-wintering. This study focused on how trypanosome gut parasite reacts to acidity and temperature. The ability of parasites to survive gut conditions has relevance for the treatment of bees by oxalic acid, the use of probiotics to improve bee health, and the consideration of hive management that affects colony temperatures. The tolerances were established for two honey bee parasites, and suggestions were development for the use of this information in improving bee health. The results are important for both honey bee and bumble pollinators and the management of disease.

Technical Abstract: Host temperature and gut chemistry can shape resistance to parasite infection. Heat and acidity limit intracellular trypanosomatid infection in warm-blooded hosts and could shape infection resistance in insects as well. The colony-level endothermy and acidic guts of social bees provide a unique opportunity to study how temperature and acidity shape insect-parasite associations. We compared the temperature and pH tolerance of three trypanosomatid parasites from honey bees with related, otherwise ecologically similar trypanosomatids from heterothermic mosquitoes with high gut pH. Relative to the mosquito parasite, all three bee parasites had higher heat tolerance, with parasite tolerance reflecting the extent of endothermy in hosts. Heat tolerance of the honey bee parasite Crithidia mellificae was exceptional for its genus, implicating honey bee endothermy as a filter of parasite establishment. Both honey bee parasites also showed striking tolerance to acidic pH's found in bee intestines. In contrast, the mosquito parasites were tolerant of the alkaline conditions found in the mosquito midgut, supporting the hypothesis that gut pH—as well as temperature—structures host-parasite specificity. Elucidating the roles of host temperature and gut pH in infection—and corresponding parasite adaptations to these factors—could help explain insect disease ecology and trypanosomatid invasion of mammals.