The impacts of predators and parasites on wild bumblebee colonies

1. The study of wild bumblebee nests has been hindered by the difficulty in locating and observing them. Here, 47 wild nests were located using a sniffer dog and volunteers. The entrances to 32 nests were filmed continuously to identify successful nests (those that produced gynes) and observe vertebrate species interactions. 2. Of the 47 nests, 71% and 21% produced gynes in 2010 and 2011, respectively. 3. A total of 39 vertebrate species were filmed at entrances but the majority did not interact with the nests. Great tits (Parus major) depredated or attempted to depredate bees on 32 occasions at the entrances to 10 nests, something that has not previously been described. Small mammals were very often recorded accessing entrances to bumblebee nests, but whether they depredated bees was not known, and frequently visited nests were no less likely to produce gynes. Eight nests were entered by adult wax moths, Aphomia sociella. 4. The faeces of 1179 workers from 29 Bombus terrestris nests were screened microscopically for parasites. Crithidia bombi infections were apparent in 49% of worker bees, while Nosema bombi and Apicystis bombi were present in 5.5% and 0.68% of bees, respectively. Nests with a high prevalence of C. bombi infection were less likely to produce gynes, the first evidence of a direct impact of this common parasite on bumblebee colony reproduction in wild nests. 5. Overall, our data indicate that bumblebee nests are at the heart of a rich web of interactions between many different predator and parasite species.