Chalk Brood Attacking a Wild Bee

Abstract

A PIECE of partly decayed deal tunnelled by an insect received for identification in September from Acton, London, was found to contain the nest of a leaf-cutting bee, probably a Megachile sp. The wood had been split for firewood and only one cell of a series in the tunnel remained intact. The cells were formed by lining the tunnel with pieces cut from hawthorn leaves and contained a dead pupa and a food store consisting of a pellet of pollen massed together with honey. The pollen proved to be that of a composite with spiny grains 36–42 μ in diameter comparable in size and ornamentation with those of the creeping thistle, Cirsium arvense Scop. The purity of the pollen store suggests that this wild bee confines its attention to one species of plant at a time, a habit regarded as characteristic of the honey bee. The pupa and pollen store were invested with a white mycelium in which small black fruiting bodies were observed. On examination the fungus proved to be Pericystis apis Maassen, the pathogen responsible for the chalk brood disease of the honey bee. We are not aware of earlier records of this fungus attacking wild bees, though this may not be due to a scarcity of the fungus but to the infrequency with which such material comes under the notice of a mycologist.