Summary: Spatio-temporal dynamics of bumblebee nest parasites
(Bombus subgenus Psythirus ssp.) and their hosts
* and Mike Edwards2
Biology Department, University of Virginia, Charlottesville, VA 22904, USA; and 2
Bees, Wasps and Ants Recording
Society, Midhurst, West Sussex GU29 9LB, UK
1. A 39-year bumblebee data base was used to study the codistribution of six cuckoo bumblebees
in the subgenus Psythirus of Bombus (hereafter called Psythirus) and their free-living bumblebee
hosts in the British Isles.
2. A model of nest parasitism predicted host threshold densities and stable deterministic dynamics,
with fluctuations only emerging as a result of environmental or demographic stochasticity.
3. Standardized transects indicated that variation in total number of records could be largely
attributed to variation in observer effort; analyses were therefore carried out using relative abun-
4. Spatially, parasite-free zones were evident in areas of low host abundance, but the host thresh-
old for parasite presence differed among species and locations.