NOTES ON SOME SUFFOLK SAWFLIES E . MILNE-REDHEAD
The following notes on sawflies (Hymenoptera: Symphyta) are written by one who IS not an entomologist, but they may be of interest to those who, like me, are interested in ecology in its widest sense, namely the interrelationships of plants and animals. Sawflies are generally wasp-like, but they lack a 'wasp waisf, the abdomen being broadly joined to the thorax. The larvae are caterpillar-like but have 6 to 8 pairs of abdominal prolegs in place of the normal 5 pairs of true caterpillars. These prolegs lack the chitinized crochets or hooks of lepidopterous caterpillars. Some sawflies are small, a few are large, but most are medium sized. The larvae can seriously defoliate plants. On the Suffolk Trust's Cornard Mere Nature Reserve (v.-c.26) in August 1978 I noticed that the largest stand of Meadow Rue (Thalictrum flavum), which occupies many Square yards, had been practically defoliated. I found the culprit to be a sawfly larva which was present in countless thousands. I sent a few specimens to Dr. V. H. Chambers, who told me that they were Pristiphora fuscata Benson, a species first recorded in Britain in 1943 (Benson, 1943), a Single specimen (a female) having been taken at Askham Bog, near York (v.-c. 64) in 1942; 2 males and 3 females were taken at the same place two years later. One male was collected in Wood Walton Fen National Nature Reserve (v.-c. 31, Hunts.) in 1947 and one female on T. flavum at Radwell Causeway, Felmersham (v.-c. 30, Beds.) in 1950. In 1951 Vic Chambers found one larva on the same host plant at Wheatfen Marsh Rockland, (v.-c. 27, W. Norfolk) (Chambers, 1953). So it seems that my record is the first for our county and the first recorded occurrence of this sawfly in quantity in Britain. In 1979 the numbers of P. fuscata on Cornard Mere N.R. were very much smaller, probably due to the unusual amount of standing water during the late winter and early spring. The sawfly was slightly more plentiful in 1980, and in 1981 it was defoliating some of the plants of T. flavum, but not to the same extent as in 1978. P. fuscata has four larval instars, followed without a further moult by the building of a cocoon. Chambers (1953) describes the larvae in detail. The different instar larvae differ considerably, the young larvae having colourless or dirty white abdomens, which may appear green due to food in the gut showing through the skin, but the older larvae have bright green abdomens, with a darker dorsal stripe Iined on either side by stripes of white fat globules' The adult differs from any other Pristophora species by having smoky wings. In our garden in Nayland we grow a white-flowered perennial Mullein, which I was given under what proved to be the wrong name, 'Verbascum chaixii. In June 1979 I noticed a wasp-like insect with its yellow legs hanging down Aying around this plant on hot, sunny days. Once again Vic Chambers came to my assistance and told me it was Tenthredo scrophulariae L., a large sawfly usually seen around Water Figwort (Scrophularia aquatica) in damp
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ditches and river banks. He told me that Benson gives Dark Mullein (Verbascum nigrum) as an alternative host. In August I noticed that the leaves of mv mullein were being eaten, and an inspection with a torch after dark revealed a number of sawfly larvae hard at work feeding. They were silver-grey with well-spaced black dots, larger on the sides, very much like the larvae of the Mullein Moth (Cucullia verbasci), but lacking its yellow colouration. My friend and one time colleague, Dr. I. K. Ferguson, who is an expert on the genus Verbascum, whom I had consulted regarding the identification of my white-flowered mullein, told me that it was the rare, white-flowered form of V. nigrum, a determination with which the sawfly clearlv agreed! I saw some of their larvae feeding up to the middle of September, but could see no sign of them in daylight. T. scrophulariae and its larvae were present again in 1980 but were not seen in 1981. In the churchyard at Shelley (v.-c.26, West Suffolk) in August 1980, the larvae were seen feeding on V. nigrum in broad daylight. Three other species of Verbascum in our garden do not appear to attract T. scrophulariae however, possibly because it dislikes their dense covering of hairs. A m o n g the weeds in our garden is a colony of Blue Pimpernel (Anagalis foemina). I was weeding out a tangle of this and Field Bindweed (Convolvulus arvensis) in August 1981 when I noticed several sawfly larvae that had fallen to the ground. I put some of them in a cage with samples of both plants and discovered that they fed on Anagalis. I sent two larvae to Vic Chambers who thought that they might be Monostegia abdominalis (Fab.), the only sawfly recorded from Anagalis, its more usual host-plant being Creeping Jenny (Lysimachia nummularia). Later he told me that he had bred out these sawflies and that his guess had been correct. It is remarkable that this sawfly. clearly restricted in its habitats through lack of food plant, should have discovered a small patch of A. foemina in my garden. We have two species of Ajuga in the garden, the purple-leaved form of Ajuga reptans (Bßgle) and the annual Ajuga chamaepitys (Ground Pine). It would be difficult to find two species in a relatively small genus looking more different. Their habit, one a creeping perennial, the other an erect annual. their leaf shape and their flower colour which are completely dissimilar, and their scent, the Bßgle being without glands and scent, whilst the Ground Pine being densely glandulär and smelling strongly of turpentine. Yet the sawfly, Athalia cordata Lepeletier, 'recognises' them as related plants, being busy around both species on most summer days, yet it is never seen anywhere eise in the garden. I have never seen the larvae, and I wonder if any member can teil me on what part of these Ajuga species they feed?
Acknowledgements I am most grateful to my friends Vic Chambers for names and information about sawflies and Keith Ferguson for naming my white-flowered Verbascum.
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References Benson, R. B. (1943). A new British sawfly of the genus Pristiphora Latreille (Hym., Symphyta). Entomologist's mon. Mag. 79, 180. Chambers, V. H. (1953). The Iarvae of Pristiphora fuscata Benson (Hym., Tenthredinidae). Entomologist''s mon. Mag. 89, 231. E. Milne-Redhead, Parkers, 43 Bear Street, Nayland, Colchester.
Trans. Suffolk Nat. Soc. 18 part 4.