Plagiotrochus quercusilicis (Fabricius, 1798), a Gall Wasp on Quercus ilex new to Suffolk.

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GALL WASP NEW TO SUFFOLK

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PLAGIOTROCHUS QUERCUSILICIS (FABRICIUS, 1798), A GALL WASP (HYMENOPTERA: CYNIPIDAE) ON QUERCUS ILEX (HOLM OAK), NEW TO SUFFOLK J. P. BOWDREY Introduction Quercus ilex (Holm or Evergreen Oak) was introduced to the British Isles as an ornamental tree c.1500 A.D. (Mitchell, 1978) and has since been widely planted, especially in coastal areas, due to its tolerance of wind and salt spray. As well as these deliberate plantings, the ability to produce viable seed has enabled the tree to colonise wide areas, for example on the Suffolk coast (Sanford & Fisk, 2010). The cynipid Genus Plagiotrochus is native to southern Europe where its species induce galls on the evergreen oak species: Quercus ilex (Holm Oak), Quercus coccifera (Kermes Oak) and Quercus suber (Cork Oak) (Nieves-Aldrey, 2001); none of these tree species being native to the British Isles. However, since 2004, three species of Plagiotrochus, all inducing galls on Quercus ilex only, have been recorded as new to the United Kingdom, namely, P. quercusilicis (Fabricius,1798) (Hancy & Hancy, 2004), P. australis (Mayr, 1882) and P. coriaceus (Mayr, 1882) (both Robbins, 2007). A study on invading cynipids by Begg (2007) reported that these species had not spread from their original discovery sites in Cornwall and Wales, but by 2018, P. quercusilicis had reached the East coast of England. These recent new records mean that the genus is not included in the review by Morley (1935). The origin of these three new species is uncertain, but it is likely that they became established as a result of accidental introduction by man, rather than natural immigration from the Continent. In 2018, a recording scheme for introduced species of cynipids using iRecord was started and soon records of P. quercusilicis began to be posted on the British Plant Galls Facebook Group ranging across southern England and extending eastwards to Suffolk and as far north as Norwich. Suffolk Records The first Suffolk record of sexual generation leaf galls of Plagiotrochus quercusilicis was made at Westleton Common in East Suffolk (TM442685) on 16.v.2018 (JPB) (Plate 1). Small reddish swellings were noticed on the midrib of young leaves on the tips of branches of a mature Holm oak, keying out to Plagiotrochus quercusilicis in Redfern & Shirley (2011). These galls were too young to attempt rearing of adults, but I decided to check other local sites where I had seen Holm oaks in the past, but had not found any galls other than the erineum induced by the widespread eriophyiid mite Aceria ilicis (Canestrini). Subsequently, Plagiotrochus galls were found at Dunwich Heath (TM477681, 9.vi.2018), Halesworth churchyard (TM384773, 10.vi.2018), Kelsale, Curlew Green (TM380653, 18.v.2018), Sizewell A (TM473630, 29.v.2018), Sizewell cliffs (TM4761,

Trans. Suffolk Nat. Soc. 54 (2018)


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