Abstract

Bombus terrestris queens may contract infections of the trypanosome parasite Crithidia bombi from their natal nests; alternatively, the queens may also become infected after leaving their natal nests while

foraging on contaminated flowers. We expected that, because C. bombi adapts to the natal colony during the previous generation, C. bombi infections from the natal colony will be more damaging to queens than a novel

infection acquired from an unrelated colony. To test our prediction, we used queens exposed to three treatment groups: natal infection, novel infection, and control (no infection). We found that the infected queens produced fewer males and had a lower overall fitness, but we did not find any differences based on the source of the infections.

We noted a strong matriline effect on the likelihood of a queen surviving hibernation and successfully founding a colony. Taken together, our results suggest that while C. bombi affects the fitness of B. terrestris, one vertical transmission event is no more damaging than randomly encountered infections. Furthermore, we found that, at least under laboratory conditions, matriline effects on fitness could override the effect of infection status.