Transmission dynamics of bee parasites
TRANSMISSION OF BEE PARASITES ON FLOWERS
Many bee parasites and diseases are transmitted via flowers. When the feces of an infected bee lands on a flower, the next bee visiting that flower can become infected. As a result, flower fields can act as hotspots for disease transmission. Given the wide variety of flower shapes and sizes, I wanted to understand how flower morphology influences different steps of the transmission process, including: 1) the probability of a flower catching bee feces, 2) the survival of the parasite on the flower, and 3) the acquisition of the parasite by new bees.
I found that flowers with long, narrow corollas have the highest transmission potential. Models based on plant species identity are better at predicting feces deposition and parasite survival, while models based on floral traits are more effective at predicting parasite acquisition.
Check out this video with the preliminary results and the paper with the final results.
WITHIN-COLONY TRANSMISSION OF PARASITES
Bee colonies have a high density of individuals and frequent interactions among them, providing parasites and diseases the opportunity to spread within the colony. I tested how quickly two different parasites spread within bumble bee and honey bee colonies and how the initial number of infected bees in the colony influences the spread of the parasites. I used Crithidia bombi for bumble bees and Nosema ceranae for honey bees. My findings showed that for both parasites, when the initial number of infected bees is small, the social immunity of the colony can effectively control the spread of the parasites. However, when approximately 30% of bees in the colony are initially infected, the parasites spread rapidly. This suggests that controlling environmental exposure to parasites can significantly reduce within-colony transmission.
Check out a video about this experiment and the paper with the final results
TRANSMISSION TO OTHER BEE SPECIES
Many bee species share flower resources, so when a parasite is present on a flower, it may come into contact with bee species other than its primary host. Exposure to an alternative host can influence the evolution of parasite virulence, as the parasite must adapt to the new host. Previous studies have identified the leaf-cutter bee (Megachile rotundata) as an alternative host for Crithidia bombi. I investigated how serial passages of C. bombi on this alternative host affect its virulence and infectivity in both the primary host (bumble bees) and the alternative host (leaf-cutter bees).
My results showed that serial passages of C. bombi on leaf-cutter bees increased its infectivity but not its virulence in the alternative host. In contrast, the virulence and infectivity of C. bombi in bumble bees initially decreased after passing through leaf-cutter bees. These findings support the idea that increasing host diversity can limit parasite specialization on a single host species.
You can read the full report here.