Diplolepis rosae

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, bédégar, and is ultimately from the Persian, bād-āwar, meaning 'wind-brought'.[3] Robin in Robin's pincushion refers to the woodland sprite of English folklore, Robin Goodfellow.[4]

A week after the egg has been laid, the larva hatches and begins to feed on the leaf bud tissue. This activity stimulates (in a way not yet understood) the development by the host plant of enlarged 'nutritive' cells in the area around the growing larva. These are fed on by the larva and are continually replaced by new cells. Further concentric layers of tissues develop around the core nutritive tissue and come to form the structure known as the bedeguar, complete with the outermost and characteristic fibrous outgrowths that give the gall its alternative name of Robin's pincushion. As the larva feeds and grows within this gall, it probably undergoes five larval instar stages (the growth stages between moults). The final instar stage is reached by late October. The larva ceases feeding. It now passes into the prepupal stage, in which form it overwinters inside the gall. In the following February or March, the prepupa undergoes a final moult and becomes a pupa. Through the thin, transparent skin of the pupa, it is possible to see the fully formed antennae, legs, wings and body segments of the adult wasp. As stated earlier, the adult wasps which start to emerge from the rose bedeguar will be mostly female, and these females will go on to lay eggs through parthenogenesis.[9] The adults begin to emerge from the old galls, which are still attached to the rose, in May. Emergences may continue through to August. No alternation of generations exists in this species.

As stated, males are known, but are very rare.[11][12] One possible reason for this scarcity is the presence of a bacterium in the genus Wolbachia, which is endosymbiotic in the females' gametes.[13] A female infected with Wolbachia 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.[6]

A gall in late autumn prior to the emergence of the gall flies

Closeup of vacated or predated galls cells

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 predation by birds or small mammals has taken place.[14]

The bedeguar is a good example of a complex community of insects.[15][16][17] The cynipid wasp Periclistus brandtii is an inquiline that lives harmlessly within the bedeguar gall and like Diplolepis rosae itself, is often parasitised by insects referred to as parasitoids or even by hyperparasitoids in some cases.[18]

The gall-wasp Periclistus brandtii causes no gall itself, but deposits its eggs in the bedeguar tissues on which the larvae feed. In turn, these larvae may be parasitised by a chalcid wasp, Eurytoma rosae, which works its way from one inquiline's cell to the next. The parasitoid ichneumon Orthopelma mediator lays its eggs directly into larvae of D. rosae, killing them. The chalcid wasps Eurytoma rosae and Glyphomerus stigma can attack both the larvae of D. rosae and of the inquiline P. brandtii. These parasitoids may in turn be attacked by hyperparasitoids such as the chalcids Caenacis inflexa and Pteromalus bedeguaris. The mossy and sticky filaments of the gall are clearly ineffective in preventing the entry of inquilines, predators, parasitoids and hyperparasitoids.[19]

The tissues of the bedeguar gall are frequently attacked by the parasitic fungus Phragmidium subcorticum, more so than the other parts of the host rose plant.

Rose bedeguar galls and rose hips in autumn

The galls occur more commonly on plants under stress, i.e. very dry conditions, waterlogging or hedge cutting, whereas 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 galls than old and intact ones. In the latter, many eggs are laid, but the number of galls formed is relatively few.

The relative number of parasitoids decreases with increasing gall volume.[20] And the closer the gall is to the ground, the greater the total number of adults that emerge. Thus, it seems more effective for a female D. rosae to induce larger galls on lower branches of the shrubs to increase the survival probability of the offspring. The distances from margins of shrubs, however, affects neither the parasitoid ratio of galls nor the volume of the galls.[6]

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, the gall was used to treat colic,[6] as a diuretic, and as a remedy against toothache; the ashes mixed with honey and applied to the scalp were thought to prevent baldness.[21] 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.[22]

• Rose Bedegaur or Robin's Pincushion video
• Video footage of Scottish galls
• "Gall". Infoplease encyclopedia. Retrieved March 2006. Check date values in: |access-date= (help)
• Photographs of the gall wasp and gall