Diplolepis lay up to sixty eggs within each leaf buds using their ovipositor. The asexual wasp emerges in spring; less than one percent are males.
A similar gall is caused by Diplolepis mayri, but this is much less common.
Being so prominent and interesting in appearance this gall has more folklore attached to it than most. The term 'Bedeguar, Bedegar or Bedequar' comes from a French word, bédegar, and is ultimately from the Persian, bād-āwar, meaning 'wind-brought.' Robin in Robin's pincushion refers to the woodland sprite of English folklore, Robin Goodfellow.
The females insects are about 4 mm/0.2 in long; parts of their abdomens and legs are yellow-red, while the rest of the body is black. The male is black and lacks the hypopygium structure which clearly identifies the species in the female. Its legs are bi-coloured yellow and has a body length of about 3mm.
The bedeguar gall is surrounded by a dense mass of sticky branched filaments. This structure gives the appearance of a ball of moss and its filaments are often brightly coloured, being at their best in around September; starting off green and then passing through pink and crimson to reddish brown. A large specimen can be up to 10 cm in width. The larvae develop and then over winter as pupae in the now brown and dry looking structure, emerging in May. The unilarval chambers are set in a woody core which persists after the filaments have worn off.
The bedeguar may also develop on Rosa rubiginosa, R. dumalis, or R. rubrifolia.
The gall induced by D. mayri differs in being more sparsely covered in short, unbranched filaments and the galls usually develop on the twigs.
As stated, the wasps emerging from the Rose bedeguar will be mostly female, and these females will go on to lay eggs through parthenogenesis. The adults emerge from the old galls, which are still attached to the rose, in May. No alternation of generation exists in this species.
As stated, males are known, but are very rare. One possible reason for this scarcity is the presence of a bacterium named Wolbachia which is endosymbiotic in the females gametes. A female infected with Woolbachia produces only diploid eggs, when in the cells of the ovaries presumably cause the fusion of the pronuclei, which leads to entirely female progeny. When the females were treated with antibiotics they were then able to produce normal male and female eggs.
Some herbivorous insects therefore create their own microhabitats by forming, in this case, a highly distinctive plant structure called a gall, comprised of plant tissue, but controlled by the insect. Galls act as both the habitat, and food sources for the maker of the gall. The interior of a bedeguar gall is formed from the bud, and is composed of edible nutritious and structural tissues. Some galls act as "physiologic sinks", concentrating resources in the gall from the surrounding plant parts. Galls may also provide the insect with some physical protection from predators.
Mature galls are sometimes broken open by vertebrate predators to recover the larvae or pupae. The large size of the emergence holes of the individual cells sometimes suggests that predation by birds or small mammals has taken place (See photo).
The bedeguar is a good example of a complex community of insects. A number of inquilines live harmlessly within the bedeguar gall and some of these, as well as Diplolepis itself, are parasitised by insects referred to as parasitoids or even hyperparasites in some cases.
The gall-wasp Periclistus causes no gall itself, but deposits its eggs in the bedeguar tissues. In turn its larvae may be parasitised by a chalcid wasp, Eurytoma, which works its way from one inquiline's cell to the next. Several parasites, such as ichnemons and chalcids, lay their eggs directly into larvae of D. rosae, killing them. The chalcid wasp Oligosthenus attacks both the larvae of D. rosae and of inquilines such as Periclistus. These parasites may in turn be attacked by hyperparasites such as the chalcid Habrocytus bedeguaris and H. periclisti. It is clear that the mossy and sticky filaments of the gall are ineffective against preventing the entry of inquilines, predators, parasites and hyperparasites.
The tissue of the bedeguar gall are frequently attacked by the parasitic fungus Phragmidium subcorticum, more so than the other parts of the host rose plant.
The galls occur more commonly on plants that are under stress, ie. very dry conditions, waterlogging or hedge cutting, where as vigorously growing plants are less commonly found to have galls. Whether the vigorous plant suppresses gall formation or is avoided by the wasp in favour of easier targets is unknown. Young and damaged plants tend to produce larger and more numerous than old and intact ones. Many eggs are laid but the number of galls formed is relatively few.
The relative number of parasitoids decreases with increasing gall volume. The vertical distance between gall and soil affects the total number of emerged specimens. The distances from margins of shrubs does not affect nor the parasitoid ratio of galls, neither the volume of the galls. It seems better for a female D. rosae, to induce larger galls on the lower branches of the shrubs in order to increase the survival probability of the offsprings.
Removing and destroying galls before they dry and the wasps emerge may help to reduce the infestation. While fairly large, and sometimes present in quite large numbers on scrub specimens, they cause no measurable harm.
Dried and powdered it was used as to cure colic, as a diuretic and as a remedy against toothache; the ashes mixed with honey and applied to the scalp were thought to prevent baldness. It was also valued as an astringent and for its ability to control fluid loss; placed beneath a pillow it was thought to induce sleep.