Transactions of the Norfolk and Norwich Naturalists' Society
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BRITISH MUSEUM = INATUfiAL HISTORY) -5 AUG 1991 EXCHANGED (KNERAL LIBRARY TRANSACTIONS of THE NORFOLK & NORWICH NATURALISTS’ SOCIETY Vol. 29 Part 1 (July 1991) TRANSACTIONS OF THE NORFOLK AND NORWICH NATURALISTS’ SOCIETY ISSN 0375 7226 Volume 29 Part 1 (July 1991) Editor R.E. Jones OFFICERS OF THE SOCIETY 1990-1991 President: K.C. Durrant Vice-Presidents: R. Baker, P.R. Banham, A.L. Bull, K.B. Clarke, E.T. Daniels, D.A. Dorling, K.C. Durrant, R. Jones, Mrs J. Robinson, M.J. Seago, F.J. Taylor Page Chairman: Mrs A. Brewster, “Four Winds”, Corpusty, Norwich, NRll 6QQ Secretary: A.L. Bull, “Hillcrest”, East Tuddenham, Dereham NR20 3JJ Asst. Secretary: Mrs J. Negal, “Inishmore”, Newton Flotman Treasurer: D.A. Dorling, 6 New Road, Hethersett, Norwich NR9 3HH Asst. Treasurer: M.J. Woolner, 45 Gurney Road, Norwich NR5 OHH Membership Committee: R. Haney (Chairman), C.Dack (Secretary) Programme Committee: M. Ewles (Chairman), Mrs C. Haines (Secretary) Publications Committee: R. Jones (Chairman), A.G. Irwin, M.J. Seago, R. Haney (Editors) Research Committee: P.R. Banham (Chairman), E. Cross (Secretary) Hon. Auditor: J.E. Timbers, The Nook, Barford Elected Members of Council: (Retiring 1991) R.E. Jones, G. Philips, E.M. Thain, B. Sage (Retiring 1992) N. Carmichael, J. Dawson, M. Hall, A. Leech (Retiring 1993) G.Maybury, Miss J. Smith, M.P. Taylor, Miss J. Wakefield Co-opted and Representative Members of Council: Dr Irwin (Museum) serves as an officer. Dr W. Sutherland (University) R. Hobbs (Norfolk Naturalists Trust), P.W. Lambley (Nature Conservancy Council) REFEREES OF PRINCIPAL SPECIALIST GROUPS Birds (Editor of the Report): M.J. Seago, 33 Acacia Road, Thorpe St Andrew, Norwich NR7 OPP Mammals (Editor of the Report): R. Haney, 124 Fakenham Road, Taverham NR8 6Qh Bats: J.G. Goldsmith, Castle Museum, Norwich NRl 3JU Amphibia & Reptiles: J. Buckley, 22 Aurania Avenue, Norwich Higher Plants: A.L. Bull, “Hillcrest”, East Tuddenham, Dereham (East Norfolk) Mrs G. Beckett, Bramley Cottage, Stanhoe, King’s Lynn PE31 8QF (West Norfolk) Mosses & Liverworts: C.R. Stevenson, 111 Wootton Road, King’s Lynn Algae: K.B. Clarke, Decoy House, Browston, Great Yarmouth Fungi: R.E. Evans, “Chantrelle”, Church Road, Welborne, Dereham Insects: K.C. Durrant, 18 The Avenue, Sheringham NR26 8DG Mollusca: R.E. Baker, 25 Southern Beach, Mulbarton NR14 8BU Marine: Dr R. Hamond, Scaldbeck, Morston, Holt, NR25 7BJ Freshwater: R.J. Driscoll, Castle Museum, Norwich NRl 3JU Photography: R. Robinson, 5 Southern Beach, Mulbarton NR 14 8BU FRONT COVER : Male and female mottled grasshoppers Myrmeleotettix maculatus (A.G. Irwin) PLANT GALLS THE PRESIDENTIAL ADDRESS DELIVERED TO THE SOCIETY ON 27 MARCH 1991 K.C. Durrant 18 The Avenue, Sheringham, NR26 8DG Being an entomologist but also interested in botany, I feel that I shall be bridging both sciences by giving you an address on British Galls, or cecidology as the study is termed. The word gall is derived from the latin Galla, meaning a plant gall, and it is defined as an abnormal swelling or protuberance of plant tissue stimulated by parasitic influence or symbiotic organisms. Galls can appear on every part of the host plant from the roots to the topmost leaves and flowers. They are formed entirely by the host plant itself and not by the gall-causer. When insects are involved most of the galls start to form when the larvae emerge from the eggs, but there are exceptions. The formation of these abnormalities is still not fully understood. Attempts to produce galls artificially by means of experiments have not been successful. It is thought that the larva of the causer produces a stimulus from its salivary secretions which act upon the plant tissue in a similar way to the growth-promoting hormone auxin, but there may be many other factors such as enzymes involved, as complex galls are produced with many layers of different tissues all formed in a definite pat- tern not found elsewhere on the host plant. Continental works now give keys to some 7500 separate galls, and there are over 1700 in the British Isles. They can be caused by either bacteria, fungi, mites, eelworms or insects, which include the larvae of moths, beetles, wasps, flies, aphids or plant bugs. Considering the length of time that galls have been known, it is only about 150 years since they have been studied seriously in the British Isles, then only from a botanical aspect. Gradually it was realised that insects were involved and with the aid of works produced on the continent the study became a science. The Greeks and Romans used galls in the production of inks and dyes, the greek philosopher Theophates who lived 378 to 286 BC mentioned galls in his writings. In 1892 the Ray Society began a monograph on British Phytophagous Hymenoptera (Cameron, 1892). This aroused interest amongst entomologists of the day in the gall wasps comprising the family Cynipidae. These insects range in size from 1 to 5 mms. In 1894 Dr Stratton translated into English the 1881 monograph of Dr Adler (Stratton, 1894) and this brought to light the discovery of the alter- nating generations of these gall wasps. Consequently many names had to be chang- ed when it became clear that most species possessed two distinct forms of insect and gall. Edward Connold (1901,1908,1909) produced three publications illustrated with photographs of all the then known galls in the British Isles. Soon afterwards other publications followed on other causers, mostly midges and mites. In 1963, the Royal Entomological Society produced in their handbook series keys to the British gall wasps and their galls (Eady & Quinlan, 1963). “Plant galls in Colour” (Darlington, 1968) illustrated and described most of the common galls of the British countryside in a handy pocket-sized volume. In 1985 a group of enthusiasts formed the British Plant Gall Society, and in the following year published very cheap but valuable provisional keys to all the British Tram. Norfolk Norwich Nat. Soc. 1991 29(1). 1 galls (Stubbs, 1986), a great incentive to the budding entomologist and botanist alike. In recent years many publications on general natural history have appeared which contain excellent illustrations of galls. Among them the Blandford Press colour series translated from the original Danish are most impressive. In the last 50 to 60 years many degrees have been awarded to students who have patiently unravelled the complicated life history of particular gall causers together with their parasites and inquilines. Unfortunately the insects involved do not have English names, and nearly all of them require the aid of a microscope for identification. Imagine for instance an extremely minute mite 120 of which laid end to end would make one inch, with a name like Eriophyes laevis inagulis—ii is enough to put all but the most enthusiastic student off their study. One of the most common and easily recognised galls is the oak apple (Plate 4). When mature it does resemble a small apple both in colour and shape. It is caused by a parthenogenetic female wasp called Biorhiza pallida. Now Bio means life, Rhiza means root, so how does root-life explain a gall which develops on the end twigs of of the oak? This is a good example of an alternate generation first mentioned by Dr Adler in 1881. In the early part of the year usually (February or March) one of the largest species of cynipid wasp can be found crawling up the trunk of an oak tree. She is wingless and only 5mm in length. At the turn of the century she was called Biorhyza aptera (“the wingless one from the roots”). On reaching a suitable bud she deposits a number of eggs within, usually 30 to 40, repeating the operation in another bud again if she escapes predation by birds. After about a month the heads of the larvae pro- trude from the eggs and they begin to feed on the contents of the plant cells for some time before finally leaving the eggs. The gall starts to form and reaches maturity in late June. In July fully winged males and females emerge which are considerably smaller than their parent. This form used to be known as quercus-terminalis (“from oak terminal buds”). After mating the females penetrate the soil and deposit their eggs on the rootlets of the oak. The galls that eventually form resemble small walnuts about 10mm in length, although many galls may coalesce into a mass up to 60 mm in diameter. After about 16 months wingless parthenogenetic females emerge to complete the two year cycle (Fig. 1). Another interesting alternate generation concerns much smaller species. If the underside of oak leaves are examined in late summer the number of minute galls which are found to cover the surface is phenomenal. Up to 300 have been recorded from one leaf with more than one species being present. These are called spangle galls and there are four common types. The larger flat galls illustrated are the com- mon spangle and are caused by the bisexual generation of a minute wasp Neuroterus quercusbaccarum, while the rounder more beautiful ones are appropriately named silk button galls caused by another wasp Neuroterus numismatis (Plate 3). Despite their size the larvae of these wasps have peculiarities in common with many other cynipid larvae. They possess extremely small mouth parts so that all they can do is pierce the plant cells and imbibe the liquid content, unlike the in- quilines which,because of their larger mouthparts, can devour the entire cells. The mid gut of the Neuroterus larva is not connected to the hind gut and therefore no excretory matter is passed until it emerges as an adult in the spring of the following year (the ultimate constipated animal).