The evolutionary ecology of a nematode-bumblebee host-parasite interaction

The nematode worm, Sphaerularia bombi, was the first parasitic nematode of insects to be described. It has a fascinating life-history. Female worms invade and infect bumblebee queens as they hibernate over-winter in the soil. The worms then evert their uterus, so it is outside their body and floating in the blood cavity of the bee. When the bumblebee queen comes out of hibernation, the worm grows quickly, castrates the bee, and turns it into a vehicle for parasite transmission. Like a pilot of a 'plane, the worm makes the bee fly to hibernation sites, land, and dig. Whilst the bee is digging the worm releases larvae into the soil. These larvae mature, mate, and then the mated female worms hang out until the late summer and autumn, when the next generation of bumblebee queens come to hibernate, at which point the cycle begins again.

We have an ongoing interest in investigating the relationship between the worm and the bumblebee hosts. We are particularly interested in the impact of the worm on the bees, how the worm avoids the bee's immune system, and the co-evolutionary dynamics of the system. PhD projects by Mike Kelly, Joe Colgan, and Catherine Jones have started to provide answers to these questions.

This work has been funded by Science Foundation Ireland, BBSRC, and the Leverhulme Foundation.

A nematode mother worm (centre) with part of her everted uterus

Two everted uteri dissected out of an infected bumblebee queen. The black one has been melanised by the bumblebee's immune system