NOTES ON SUFFOLK GALL INDUCING HYMENOPTERA

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Suffolk Natural History, Vol. 46

NOTES ON SUFFOLK GALL INDUCING HYMENOPTERA INCLUDING ISOCOLUS SCABIOSAE (GIRAUD, 1859) (HYMENOPTERA: CYNIPIDAE) AND OPHELIMUS ? MASKELLI (ASHMEAD, 1900) (HYMENOPTERA: EULOPHIDAE) NEW TO THE COUNTY JERRY BOWDREY Abstract Two new Hymenopteran gall inducers are added to the Suffolk list and additional, recent records of other gall-inducing Cynipidae are given. Introduction Recent field work has added two new species of gall-inducing Hymenoptera to the Suffolk list. These include a previously overlooked native species as well as a new UK coloniser. Unless otherwise stated, all records are the author’s. Cynipidae: Aulacidinae A visit to Clare Country Park (TL7745) on 26 September 2009 provided the opportunity to search for galls on Centaurea scabiosa (Greater Knapweed), a plant that is frequent along the old railway line track at that site. There are currently three cynipid species recorded as galling this plant in Britain, Phanacis centaureae which galls the stems internally and was also present at Clare, Isocolus fitchii galling the base of the stem and I. scabiosae galling both stems and bracts. Isocolus scabiosae (Giraud, 1859) form rogenhoferi Wachtl, 1880 Several bract galls induced by I. scabiosae f. rogenhoferi were located in seedheads of C. scabiosa at Clare. They are revealed by scraping aside the ripe seeds to expose the inner surface of the bracts. I. scabiosae is an unusual gall wasp in that it is capable of inducing two very different types of gall on different parts of the host plant. One type of gall is multilocular and forms an irregular swelling at the base of the stem of the plant, the other is unilocular and occurs in the involucral bracts of the flower. The bract gall was formerly known as I. rogenhoferi (Eady & Quinlan, 1963), but this has now been downgraded to the status of a form (Nieves-Aldrey, 2001). Galled bracts are detectable in the flower heads of the plant as hard swellings on the inside wall of the flower. The galls are hard and shiny, measuring about 5 mm × 3 mm and are situated at the base of the bract (Figs. 1 & 2 show a fresh gall and one with the emergence hole of I. scabiosae). The galls are not usually visible from the outside, although they may cause slight irregular distortion of the flower in some cases (pers. ob.). This cryptic habit probably results in the species being under-recorded. The gall wasp usually emerges in June or July of the following year, the gall remaining attached to the dead flower head throughout the winter. Occasionally, however, emergence holes can be found in galls in August and September of the same year as gall formation (Fig. 3). These have been attributed to chalcid parasitoids which more usually emerge the following year (Niblett, 1942).

Trans. Suffolk Nat. Soc. 46 (2010)


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