Clodronate liposomes untangle the role of hemocytes in Apis mellifera response to temperature variation and microbial infection

Authors: OETH, MICHAEL - University Of Southern Mississippi; KUMAR, DEEPAK - University Of Southern Mississippi; GOBLIRSCH, MICHAEL - US Department Of Agriculture (USDA); Alburaki, Mohamed; ADAMCZYK, JOHN - US Department Of Agriculture (USDA); KARIM, SHAHID - University Of Southern Mississippi

Submitted to: Journal of Innate Immunity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/19/2025
Publication Date: 1/8/2026
Citation: Oeth, M., Kumar, D., Goblirsch, M., Alburaki, M., Adamczyk, J., Karim, S. 2026. Clodronate liposomes untangle the role of hemocytes in Apis mellifera response to temperature variation and microbial infection. Journal of Innate Immunity. https://doi.org/10.1159/000550255.
DOI: https://doi.org/10.1159/000550255

Interpretive Summary: This study sheds new light on how honey bee immune systems, specifically their blood cells, or hemocytes, respond to the dual challenges of temperature fluctuations and bacterial infections. By using a special technique to remove certain blood cells in honey bees for the first time, we discovered that each type of cell plays a vital role in keeping the bees healthy. The depletion of these cells made bees more susceptible to infection, particularly in warmer conditions. Interestingly, cooler temperatures appeared to mitigate the effects of immune suppression, suggesting that environmental conditions can buffer physiological vulnerabilities. Age also emerged as a key factor: younger bees (nurses) had more robust hemocyte counts and appeared more resilient, whereas older foragers showed diminished immune capacity and greater sensitivity to temperature and infection. This reflects a potential trade-off in bee colony labor division, where older bees may be more expendable from an evolutionary standpoint. Ultimately, this work not only confirms that hemocyte responses are both cell-type- and age-dependent, but also demonstrates the power of this special technique as a new method to experimentally probe insect immunity. The findings have potential relevance for understanding honey bee health in the face of environmental stressors and could inform beekeeping practices or strategies to mitigate colony losses.

Technical Abstract: Introduction: Hemocytes are central to honey bee (Apis mellifera) immunity, but the roles of their subtypes under combined stressors are unclear. We tested the effects of temperature and bacterial challenge on hemocyte abundance and, for the first time in honey bees, used clodronate liposomes (CLD) to selectively deplete hemocytes. Methods: Five-day-old (Nurses) and fifteen-day-old (Foragers) honey bees were treated with CLD, control liposomes, PBS, or left untreated, then exposed at either 32°C or 22°C and challenged with Escherichia coli, or Staphylococcus aureus. Survival, hemolymph volume, total hemocyte counts, and differential hemocyte counts were monitored over seven days. Results: The CLD application demonstrated significant reductions in granulocyte and prohemocyte populations, indicating the highest vulnerability. A temperature drop to 22ºC buffered the negative impact on survival of CLD-induced immunosuppression. While bacterial challenges universally reduced hemocyte counts, we found a fundamental age-dependent difference where nurses maintained significantly higher baseline total hemocyte counts than foragers. Furthermore, temperature did not affect overall total hemocyte counts in 5-day-old nurse bees, but in 15-day-old foragers, it significantly modulated the hemocyte response to bacterial infection. Conclusion: Hemocyte function is subtype-specific, shaped by temperature and age, with foragers showing greater vulnerability. Clodronate liposomes provide a new tool to dissect honey bee immune–environment interactions.