Have you spotted the tufts of green and red fibrous tendrils sprouting from dogrose? These are known correctly as a Bedeguar Gall but are known to many by the colloquial name Robin’s Pincushion.
They are a type of gall – this is commonly defined as an abnormal plant growth caused by some foreign agent (such as a fungus, a mite or a wasp) which provides both food and shelter for the organism. In this case, the mechanism is a chemically induced distortion of unopened axillary or terminal leaf buds by a tiny wasp which has the latin name Dipoloepis rosae. The species name – the second of the two latin names – is rosae which refers to the intimate relationship between the wasp and the rose.
The female wasp lays her eggs on the rose and, a week later, the larvae hatch and induce the formation of the gall. The gall provides food for up to 60 larvae as they grow throughout the summer, passing through various ‘instar’ forms or life stages. Inside the centre of the gall is a woody core with chambers where the larvae spend the winter in pupal form and then begin emerging as adults in May, continuing through to August. The wasps are tiny – only 3-4mm across – and most are female.
The galls are more common on plants under ‘stressed’ conditions such as those growing in waterlogged soil or with poor nutrients, however the presence of the galls does not appear to have a significant impact on the plants.
These photographs were taken on Beacon Hill behind Grantham where many of the rose plants have been visited by the wasp, but they can be seen in hedgerows and scrub patches throughout the country.