Glyphomerus stigma

Glyphomerus stigma is an ectoparasitoid of Diplolepis rosae, D. eglanteriae, D. nervosa, Periclistus brandtii and Eurytoma rosae in the Bedeguar gall. It is also associated with other Cynipidae which include; Diplolepis centifoliae, Diplolepis eglanteriae, Diplolepis fructuum, Diplolepis fukudae, Diplolepis mayri, Diplolepis multispinosa, Diplolepis nervosa, Diplolepis opaca, Diplolepis polita, Diplolepis spinosissimae, Periclistus pirata and Xestophanes potentillae. It also is associated with Melitoma taurea from the Family Apidae.

It is partly phytopagous and once the host has been consumed it will revert to feeding from the gall tissue. If the inducer is killed by a parasitoid in early summer, nutritive gall cells degenerate into vacuolate parenchyma and are consumed. If the inducer is killed later in the summer, when galls begin to mature, nutritive cells persist in the chambers for about 1 week before degenerating. Glyphomerus stigma kills and consumes inducer larvae when galls are maturing. New nutritive cells appear under the influence of G. stigma and are then consumed. The ability of entomophytophagous chalcids to promote the formation of gall cells provides insight into the derivation of the gall-inducing guild.

The wasp emerges in early june through to early august. Its distribution is in the southern half of Britain and there may be somewhat locally distributed (Blair 1943).

The female measures an average 3.4mm with a range of 1.7-4.4mm head and body, excluding the ovipositor.
The head and body are black to dark brown, semi glossy, hairy and without any metallic colouration. The antennae are dark brown and have 7 funicular segments. The legs are brown with the hind coxae being at least twice the length of the middle coxae and have 5 tarsel segments. The wings are tinted brown all over with a large dark cloud around the stigma extending backwards. The stigmal vien is shorter than the post stigmal vein. The ovipositor sheaths are about mid length.

The male measures 1-3.1mm averaging 2.2mm
The head and body are black to dark brown, semi glossy, hairy and without any metallic colouration. The antennae are dark brown and have 7 funicular segments. The legs are brown with the hind coxae being at least twice the length of the middle coxae and have 5 tarsel segments. The wings are tinted brown all over with a large dark cloud around the stigma extending backwards. The stigmal vien is shorter than the post stigmal vein.

Blaire (1945) gives a description of the larva as white and tapering strongly towards the tail. The larva is curved into a question mark shape and the greatest thickness is about the second and third thoracic segments. The segmental divisions are not deeply constricted and a median dorsal protuberance is present on the posterior border of each of the first four abdominal segments. It has a covering of long soft hairs which are curved outwardly and ventrally. The head is transversely cordiform and is twice as wide as it is long with the middle of the frons depressed and there are two deep, elongate fossae which nearly meet above. The jaws are slender, curved and have a sharp tooth on the inner side, some distance before the apex.

More detailed descriptions and identification keys are available from Robin Williams at the British Plant Gall Society.

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