The Bedeguar Gall or ‘Moss-gall’ or ‘Robins pincushion’ can be seen on the Dog-rose (Rosa canina) and its many subspecies and hybrids. They used to be used by apothecaries as remedies for colic and as a diuretic (Bedeguar comes from a French, and ultimately a Persian, word meaning ‘wind-brought’). A gall is an abnormal growth produced by a plant or other host under the influence of another parasitic organism. The association between the causal agent and the host is usually quite specific. which means that specific causers are very selective about the plant species they associate with. It involves enlargement and/ or proliferation of the host cells and provides both shelter and food or nutrients for the invading organism. It is caused by the Gall-wasp or Diplolepsis rosae which causes galls on several species of Rosa, mostly R. canina, R. rubiginosa, R. dumalis, R. rubrifolia.
D. rosae is from the superfamily Cynipoidae, often termed as Cynipids, and in the family Cynipidae (gall forming wasps and inquilines). This family is then split further into subfamilies and then into tribes. D. rosae is found in the subfamily Cynipinae, which splits to form 4 tribes, of which D. rosae is located in Rhoditini (gall wasps which parasitise Rosa species), which consists of one genus, Diplolepis, with 6 species found in the UK.
Length of head and body is about 4mm. The head is black and the cuticle is finely punctate with both pubescent and glabrous areas. The eyes have a deep red hue and are slightly protuberant. The base of the mandibles can be either red or black. The dark brown antennae consist of 14 segments (flagellomeres) of which the first is the longest, and each subsequent one is slightly shorter than the proceeding one, excepting the terminal or last one which is annulated (made up of rings).
The Thorax (or mesosoma) is black and its dorsal surface pubescent while the ventral surface is glabrous. Three narrow grooves run longitudinally along the anterior part of the mesosoma, these are complete although sometimes very weak. These grooves consist of a medial scutal line and two lateral notaulices. The coxae (The first segment of a leg, between the body and the trochanter) bases are black or brown and the legs amber to brown. Only the tibia and tarsi are pubescent.
The wings, both fore and hind, are hyaline (clear of vein structures as found in many other wasps) and pubescent, with the hind wings posessing three hamuli (hooks used to lock the fore and hind wings together in flight) on the anterior margin (front edge).
The female gaster (abdomen) is amber to chestnut brown except for the modified last visible plate (hypopygium) on the underside, which is black, and a series of dark brown to black diamond markings along the top of the gaster, fading anteriorly. The hypopygium has what is known as a ploughshare appearance which sets it apart from many other gall wasps. The upper tergites (abdominal plates) numbers 6 and 7 are setose (bristly with slender, hair-like, usually sensory extension of the cuticle, connected to the body wall by a socket. Known individually as seta or collectively as setae)
The male gaster is black and lacks the hypopygium. Its legs are bi coloured yellow and has a body length of about 3mm.
Biology and behavior
D. rosae differs from most of the other gall wasps in only having one generation per year. The species consists almost exclusively of parthenogenic females and although males are known they are very rare. The percentage recorded varies from 4.2% to 0%, and I have to admit that I have yet to see one. They have been described by Still and Davring (1980) as being quite active but not attempting to mate when confronted with females.
The reasons for this scarcity of males may be due to a couple of reasons but as yet can not be pinned down for definate.
One theory is being widely studied is the presence of a bacteria 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 femles were treated with antibiotics they were then able to produce normal male and female eggs. For more infomation on Wolbachia,
Distribution of Wolbachia among the guild associated with the parthenogenetic gall wasp Diplolepis rosae
The ovipostor, which is 3-3.5mm in length and compared to the size of the wasp which is only 3-4mm, when not in use it is curved back up inside the body, following the contours of the gastor (abdomen)leaving only a small portion visible, protruding from the tip of the hypopygium. It is made up of a sheath and two stylets. Thickened longitudinal projections on the sheath, engage with their corresponding slots in the stylets, so that the three are locked together to form the central duct through which the egg is passed. The end of the sheath is serrated, and rows of hair like sensilla (sense organs) are arranged longitudinally on the inner surface of the tips of the stylets. These are thought to allow the female to know the exact position of the egg during ovposition. Lines of teeth like strucures are found along the lateral of the stylets that are in contact with the sheath.
The dissection of newly emerged females has shown that each ovary comprised of 30-40 ovarioles each of which contained from 6-10 eggs
The females begin to oviposite afew hours after exiting the gall and can continue for upto 3 weeks there after. The female wasp lays her eggs in the leaf buds in April/May of several different species of Rosa. This is done by the wasp exploring the plant with her antennae, which she taps on the surface, until a suitable expanding bud is found. She then orientates herself in a vertical position with the head facing downwards, or towards the base of the stem, and with the hypopygium close to the bud. The ovipositor is then uncoiled, and with the sheath held out of the way, the tip of the ovipositor is introduced under the edge of an outer bud scale. These eggs are deposited in the basel region of the first and second leaves. Most of the eggs are deposited on the median vien of the pinnules, many on their bases and on the developing petiole of the pinna. Very few are placed on the lamina of the pinnule and even rarer, though reported, into the bark of a young shoot. The female, with great precision, deposits only one egg in one epidermal cell.
Host plant preferance and selection by the female is not completly understood. It is known that species of the genus Rosa is preferred, but there are 16 species in the genus and a further 21 subspecies and varieties of Rosa canina plus hybrids. Rosa canina is certainly the most common in this country although others are also utilized.
The galls are most commonly found on the apical (shoot tip) buds or 1-15cm below the tip on leaflets and petioles, rarely on branches, pedicels or hips (fruits). 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. Schroder carried out controlled tests on vigorous and distressed plants and found the wasps layed eggs on both quite readily, though their behavior may be different in the field when a choice is provided. Young and damaged plants tend to produce larger and more numerous than old and intact ones. Shrubs growing in ecotone zones (e.g. roadsides, forest margins) have many, or larger galls. As such, the galls collected from shrubs growing in sites with increased heterogenity, appear more unique in their quantitative characteristics than those collected from homogenous sites (e.g. grassy areas without roadsides or without margins of forests). What is certain though is that there are many eggs layed but the number of galls formed is reatively few.
Numerous cavities arise, each containing one larva. 4-8 weeks after oviposition, the gall is full-sized. The young gall is green but turns red by August and can be up to 10 cm in diameter. The mature gall can be considered as a 2 part structure in concentric layers. The inner gall comprising of several chambers, each with its own resident larva, is formed of starch parenchyma and an inner lining of nutritive cells. Surrounding the inner gall is a layer of thick walled cells forming a sheath known as the sclerenchyma. The outer section of the gall is made from large parenchyma cells with the associated vascular tissue which extend throughout the gall and link the nutritive cells with the unmodified stem.
Inside it has many chambers and each one has white grub, the larva. The larva of D. Rosae consists of a yellowish white grub with 13 segments (the first two being the head, the next three form the thorax and the last 8 form the abdomen). The larva is supposed to undertake 5 instars although this is not easy to ascertain fully, due to their enclosed lifestyle. However by the third instar the larva occupies its own chamber in the gall, which then produces its characteristic multilocular structure.
By September the larva begins to develop eyes which can be seen in the second segment, along with a weakly defined head capsule (partially retracted) and the integment becomes cream coloured and transparent.
The mature, final instar larva has 2 phases. The first stage is an active feeding stage which by late October passes to the second stage of non feeding prepupal stage with out a moult. This is the stage in which it enters diapause and overwinters. Pupation occurs inside the gall chamber in February or March although some have formed as late as April. This pupa is exarate (has free appendages.) and emerges the next march/april.
Diplolepis rosae over winters in the gall emerging as adult wasps in spring. Within minutes of leaving the gall the wasp defecates the meconium that it has stored up through its larval and pupal stage. Only about 1 to 4% of the emergences are males, if any. The vast majority of adult female wasps reproduce without needing males i.e. parthenogenetically.
The Inquiline gall wasp Periclistus brandtii (Ratzeburg) is a harmless inquiline cynipid and lays its eggs on the ready-made gall, just like the cuckoo uses other ready-made nests for its eggs. Inquiline larvae cause the gall to be hypertrophied and increasing number of inquilines causes increased growth of host gall tissues and wall thickness. The P. brandtii larvae subdivide a single host larval chamber into many inquiline chambers and this fact leads to the prediction that inquiline presence will modify the gall size and the number of emerging specimens. Inquilines, particularly if they are many in a single chamber, sometimes kill the larva of the gall inducer. The number of emerged individuals was significantly higher in inquilined galls. Inquilines increase insect biomass per gall and serve as an important source of food for other entomophagous species. In the case of galls of D. rosae the presence of inquiline Periclistus brandtii involves the appearance of parasitoids like Caenacis inflexa and Eurytoma rosae. The significantly higher number of emerged individuals from inquilined D. rosae galls is due to a higher number of individuals per inquilined host chambers. Gall size increased significantly due to the growth of cellular mass of the inquilined chambers, but its magnitude was smaller than in unilocular cases. Number of emerged individuals and diversity was significantly higher. For inquiline-free galls, a highly significant positive correlation was found between gall size and number of emerged individuals. But the presence of inquiline entirely annihilated the correlation between gall size and number of emerged individuals, although this relationship is a basic truism for unilocular galls. Regarding to the complexity of the effect caused by the inquiline multilocular galls are more than just a multiple of unilocular ones. The final conclusion is that in multilocular galls the presence of inquiline species changes significantly the parameters that can contribute to the survival of the gall inducer. Thus, the presence of inquiline may affect the relation between host plant and gall inducer.
Other species of wasp larvae will also make use of the gall and (as in marble galls) a complex ecology of parasitoids and hyperparasitoids. The community may include at least fourteen species, and there are some differences in relative abundance of species between certain areas. But the main conclusion is that species composition of the communities is constant in Europe. There are the species that do not form their own galls but just utilize those already formed by others, these are inquilines. The major inquiline is Periclistus brandtii, this has a commensal relationship, i.e. it benefits from the arrangement, but does not have a detrimental affect on Diplolepis rosae. The main parasitoid of D. rosae is Orthopelma mediator
(THUNBERG 1832), which deposits the eggs dirctly into the larve of D. rosae even before the gall has started to develop, because in this case all the host larvae present in the gall can be reached.
More incidious is the possible introduction into the gall of parasitic wasp larvae that will gradually consume Diplolepis rosae such as the Chalcid Wasp Eurytoma rosae, which consumes the larvae and vegetative matter of the gall and works its way from one cell to the next, and as such can attack all species of larvae in the galls local vacinity. Also the (Torymus bedeguaris) female pierces the gall with its long ovipostor and can get at the larvae of even an older gall that would be safe from other parasites. 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. All these relationships happen in one Robins pincushion! It is clear that the mossy and sticky filaments of the gall are ineffective against preventing the entry of inquilines, predators, parasitoids and hyperparasitoids.
Parasitoids of D. rosae behave with an increased diversity, opposite to the parasitoids of P. brandtii. This increased numerical diversity in the case of Orthopelma sp., T. bedeguaris, G. stigma is due to the fact that there could be a hyperparasitic relationship: Orthopelma sp. could be parasited by T. bedeguaris, G. stigma and P. bedeguaris (NORDLANDER 1973, NIEVES ALDREY 1980). In the case of parasitoids of P. brandtii we do not have knowledge about hyperparasitic relationships. The case of T. rubi is more interesting, because it is the parasitoid of Diastrophus rubii, and we can only guess that its host is D. rosae in the bedeguar gall.
The list of inquilines and parasites reliant on Diplolepis rosae are as follows:
Identification key for Bedeguar gall exits.
The surviving ratio of D. rosae increases with growing gall volume. This relationship was observed by STILLE (1984) for D. rosae and for several other species like Diastrophus kincaidii (JONES 1983). It has been found that relative number of parasitoids decreases with increasing gall volume. The vertical distance between gall and soil seems to affect 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. So we can hypothetize that from the perspective of a female D. rosae, it would be better to induce larger galls on the lower branches of the shrubs in a homogenous environment in order to increase the survival probability of the offsprings.
Other possible threats to the galls that are non Hymenoptera comes from Circulionidae, Weevils. In particular Curculio (=balanius) villosus. Five of these weevil larva were recorded by Blair (1939) emerging from a D. rosae gall that had been collected in Frome, Somerset. This weevil is usually resident in Oak apple galls created by Biorhiza pallida and feeds on the gall tissue while fresh. It emerges when full grown to pupate in the soil. It was assumed that these five larva were feeding on the gall material itself sometimes inflicting high mortality. Curculio villosus is unusual among inquilines of cynipid galls in that it usually only attacks this one host. In non-oak gallwasp galls, the weevil Rhynchites bicolor feeds within the galls induced by the herb gallwasp Diastrophus kincaidii on thimbleberry (Rubus parviflorus), and an unknown species has been reared from Paraulax galls on southern beech (Nothofagus). I have found an adult Anthonomus rubi from a collected gall though rather than being a threat, I feel that it was merely over wintering in the join between the gall and the stem or among the filaments of the gall.
The tissues of the bedeguar gall are frequently attacked by the parasitic fungus Phragmidium subcorticium, which is a plant pathogen which causes rose rust more so on the galls than the other parts of the host rose plant.
A range of vertebrate predators extract cynipid larvae from their galls. Woodpeckers and rodents are able to open even large and heavily lignified galls, while smaller insectivorous birds can cause significant mortality in smaller, thin walled galls. I have seen many galls that have had one side of the gall opened up and the larvae inside are missing, all that is left is a number of partially open empty larval chambers which have become dried out and hard so I am assuming that they were emptied when the gall wall was softer, before it matured.
More detailed descriptions and identification keys are available from Robin Williams at the British Plant Gall Society.
More detailed and background information can be found at “Randolph, S.(2005).The Natural History of the Rose bedeguar gall and its Insect Community.”
British Plant Gall Society, Suffolk. ISBN 0-9511582-2-8