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Eurytoma rosae

This parasitic wasp is not common in the UK and counts as a small percentage of gall exits, quoted by Askew (1980a) as as small as 2.3% of exits for Britain, from samples in Buckinghamshire, Lancashire, Lincolnshire, Oxfordshire and Yorkshire.

It feeds mainly on the larvae of the Cynipidae gall wasps such as the Bedeguar gall caused by Diplolepis rosae. It mainly attacks Periclistus brandtii, and less commonly D. rosae. Other species attacked include;
Primary hostsPrimary hosts Plant associates
Coleoptera (Beetles);
  • Family: Buprestidae
    • Agrilus rubicola
  • Family: Scolytidae
    • Scolytus mali

Diptera (flies);
  • Family: Cecidomyiidae
    • Lasioptera rubi
    • Oligotrophus lyciicola
  • Family: Tephritidae
    • Dacus oleae
    • Myopites limbardae

Lepidoptera (Moths and Butterflies)
  • Family: Arctiidae
    • Hyphantria cunea
  • Family: Glyphipterygidae
    • Anthophila nemorana
  • Family: Tortricidae
    • Clysia ambiguella
    • Polychrosis botrana
Hymenoptera (Wasps, Bees and Sawflies)
Parasitoid hosts
  • Family: Aceraceae
  • Family: Asteraceae
    • Centaurea sp.
  • Family: Fagaceae
  • Family: Oleaceae
    • Olea europaea
  • Family: Rosaceae
  • Family: Rubiaceae

It is quite an aggressive parasite and indeed sometimes refered to as a predator rather then a parasite. In general it will not confine itself to one P. brandtii but will consune one larva then burrow through the cell walls into another cell and consume that one as well. Although stated by Nordlander in 1973, some of the smaller specimens have only parasitised on P. brandtii larva. In this way it can consume several species and is not restricted to just one and its diet is considered as entomophagous and phytophagous. This dietry behavior probably explains why the adult E. rosa are able to emerge before the host species. Although a large proportion of them seem to overwinter as larva.

Blair (1945), noted the behavior and that the galls of Periclistus brandtii often contained afew, perhaps 4-6, eggs of a different kind. From these eggs hatched the larva which where found on the inner wall of the chamber, but did not attack the Periclistus larva until later when they were sunk into the pits of the chamber. Then the Eurytoma rosae would descend into the pits and consume the larva. Once the pits had closed in then they would bite there way from one cell to another to devour another larva.

The female wasp measures 2.4-3.7mm, averaging 3.2mm
The head and body are black and granular with black antennae, consisting of one ring and 5 funicular segments. It has a large pronotum and the notaulices are deep and complete. The wings have short stigmal and post marginal veins. The legs like the body are black and have 5 tarsel segments.

The male, like the female, is black and granular but smaller at 1.4-2.6mm averaging out at 2.1mm.
The head and body are black and granular with distinctive knobbly black antennae, consisting of one ring and 5 funicular segments and halos of long white hair. The pronotum and the notaulices are deep and complete. The wings have short stigmal and post marginal veins. The legs are dark and have 5 tarsel segments. The wasp is petiolate with a short, upright gaster.

Identification of the adult Eurytoma rose wasp is difficult using morphological data and Claridge and Askew (1960) found subtle differences with the mesepisternum, mid coxa and female gaster that seperated it from most others but where unable to seperate it from adult E. brunniventris. However of the six Eurytoma species - each one attacks a different host in different plant species and as such, this would be enough to allow positive identification of the each species. As an egg the differences between the and E. brunniventris are evident. The chorion (outer shell) of E. brunniventris is closely covered in short simple spines whereas E. rosae is simple and unsculptured, and lacks any spines.

The larva was described by Blair in 1945 as moderatly slender and white. I has an enlarged second segment and tapers towards the end. It head is tranversley cordiform, or heart shaped, and its jaws have a long curved tips which overlap and a sharp tooth on the inner side behind it. There are afew long, curved hairs on the head and prothorax segments, elsewhere the hairs are short and sparse. There is a transverse median dorsal process at the base of the third thoracic segment and the next seven abdominal segments as well as lateral beading on abdominal segments one to six, immediatley above the trachial trunk.

Eurytoma rosae itself is attacked by two parasitoids, Glyphomerus stigma, and Caenacis inflexa which also attacks Periclistus brandtii.

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

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