The Entomologist - 116 (I), 28-30 (1997)

Habitat use and wing form in diptera (: )

J.A. HOLLIER, P.H.D. SMITH & S. MORTIMER, Imperial College at Silwood Park, Ascot, Berks SL5 7Px UK. Key words: Lacewings, wing form, habitat use, succession, climate change

Introduction The lacewings (Neuroptera) are a group of nocturnal and mainly arboreal predators (Fraser, 1959). As the common name suggests, one of the main characteristics of the group is the well developed, richly veined wings. is an unusual lacewing in two respects; it is mainly recorded from dense and tussocky vegetation (Kirby &Welch, 1990), and it is most often micropterous. Wing-form polymorphism is found in a wide range of , and is considered adaptive. The macropterous form can migrate to other habitat patches, while the micropterous forms may exhibit characteristics that promote high productivity such as higher fecundity or more rapid maturation (Roff, 1990). The benefits of microptery are therefore linked to habitat stability, and macroptery to the necessity of migration if local conditions become unsuitable (Novotny, 1994). It seems prob- able that the macropterous form of P. diptera is dispersive (Plant, 1994), in spite of past speculation that it is flightless (New, 1966), and that the micropterous form is found in relatively stable habitats. The recorded status of this species in Britain has changed considerably in recent years. It was considered rare by Killington (1936), and uncommon by Fraser (1959), but there has been a large increase in the number of records since the 19801s,leading Plant (1994) to regard the species as widespread but under-record- ed. Recent changes in agricultural policy have resulted in the creation of new grass- lands on land taken out of arable production, some of which represent suitable habi- tats for I? diptera. These areas could be colonised most easily by the macropterous form, which may therefore be expected to be relatively more abundant than the micropterous in such new or transient habitats.

Methods and Results The information presented is taken from three studies of the successional changes in the plant and communities of grasslands. All of these used vacuum-sam- pling methods, but were not primarily concerned with lacewings. The main information on habitat preferences comes from the survey of 47 chalk grasslands, mainly in the Chilterns, carried out in August 1994 using a D-vac. The sites sampled included a range of ancient grasslands and ex-arable fields of differ- Wing form & habitat use in l? diptera ent age. l? diptera was recorded at three of the sites, all the specimens being micropterous. The sites where the lacewing was found were those ancient grass- lands that had a tall, dense vegetation, dominated by either Arrhenatherum elatius or Bromus erectus. At Wytham Woods, near Oxford, l? diptera was recorded in August 1990 from a field on which arable cultivation ceased in 1981. Six specimens, all macropterous, were collected from two plants of Lotus corniculatus, out of about 40 sampled using a Uni-vac. The other record comes from Silwood Park, Berkshire, in July 1993 where a sin- gle macropterous specimen was collected in a D-vac sample from an experimental plot on which arable cultivation ceased in 1986. The plot was ungrazed, and its veg- etation was tall, though not particularly dense.

Discussion The pattern shown in the comparative study of 47 grasslands is in keeping with pre- vious observations, which associate l? diptera with tall, dense or tussocky vegeta- tion. It was noticable that all of the sites where the lacewing occurred in this study were ancient grasslands, confirming the suggestion that the microptrous form is associcated with more stable habitats. F! diptera was not found on ex-arable land even where this had tall vegetation and was adjacent to the sites were the lacewing was present, once again suggesting that it is a poor disperser and therefore a poor coloniser. The occurrence of macropterous specimens of this lacewing on ex-arable fields in our other two studies is therefore worthy of notice. The vegetation with which l? diptera was associated at Silwood Park was of the type usually reported, namely tall and tussocky. At Wytham however, it occurred on an ex-arable field used for grazing experiments, and consequently having areas of vegetation of different heights. Although the lacewing was not found on the short- est swards it was also absent from the longest. The presence of the species at a rel- atively high density on L, corniculatus plants at thissite may suggest an association with this species, especially since Lotus was present in the sward at the other sites l? diptera was recorded, and it too is found in a wide range of habitats. Both of these records from new grasslands on formerly cultivated land were the first for the locations, indeed the Wytham record appears to be the first for Oxfordshire (Campbell, 1993). Under-recording seems an unlikely explanation for the absence of records because both sites have been studied for many years. At Silwood Park a previous study of the lacewing fauna of the same experimental area failed to detect F! diptera (Hollier & Belshaw, 1992), althought it could be argued that because that study was based on Malaise trap data l? diptera would be less like- ly to have been recorded. Additional evidence that l? diptera has recently colonised this site comes from data on insects sampled by D-vac on the experimental area since 1977 as part of a long-term study of succession. The assemblages associated with the vegetation of 34 plots of known age were examined without finding l? diptera. It seems likely therefore that these records represent more than just very J. A. Hollier, P. H. D. Smith & S. Mortimer local colonisations, and that the macropterous form is indeed dispersive as Plant (1994) proposed. Given this evidence of active colonisation, and the recent boom in records, it is tempting to suggest that a real increase in the abundance of P: diptera is taking place, possibly facilitated by the increase in grassland on arable farmland. It should be noted however that colonisation need not lead to establishment. In his discussion of this species Plant (1994) notes that the macropterous form is reported more fre- quently at the end of hot, dry summers. It therefore seems possible that the report- ed increase in P. diptera distribution could be one of the first signs of the effects of climate change on the distribution of an insect species.

Acknowledgements We are grateful to Helen Billington, Suzie Simons and Miguel Rodriguez for help with the sampling, and to the National Trust, English Nature, and Buckinghamshire County Council for permission to sample at their sites. Thanks are due to Colin Plant for confirming the initial identification and his valuable comments.

Summary The lacewing Psectra diptera was regarded as rare in Britain until the 1980's, when an increase in records was noticed. Evidence that at least part of this increase is due to colonisation, and related to changes in land use, is presented. The apparent link between macropterous potential colonists and hot summers suggests that the increase in records may be evidence of climate change.

References Campbell, J.M. (1993) Oxfordshire Neuroptera. Neuro News 12: 4-7 Fraser, F.C. (1959) Mecoptera, Megaloptera and Neuroptera. Handbooks for the identification of British insects. Vol. 1: Parts 12-13. Royal Entomological Society of London. Hollier, J.A. & Belshaw, R.D. (1992) Changes in Neuroptera assemblages in an old field succession in southern Britain. Entomologist 111: 187-194. Killington, F.J. (1936) A monograph of the British Neuroptera. Ray Society. London Kirby, P. &Welch, R.C. (1990) Notes on the habits and habitats of Psectra diptera. Neuro News 7: 4- 10. New, T.R. (1966) Some notes on the biology of Psectra diptera (Burm.) (Neuroptera, Hemerobiidae). Entomologists Gazette 17: 79-82. Novotny, V. (1994) Relation between temporal persistance of host plants and wing length in leafhop- pers (Auchenorrhyncha: Hemiptera). Ecological Entomology 19: 168-176. Plant, C.W. (1994) Provisional atlas ofthe lacewings and allied insects (Neuroptera, Megaloptera, Raphidioptera and Mecoptera) of Britain and Ireland. I.T.E. Monks Wood. Roff, D.A. (1990) The evolution of flightlessness in insects. Ecological Monographs 60: 389-421. Bibliography of the Neuropterida

Bibliography of the Neuropterida Reference number (r#): 8910

Reference Citation: Hollier, J. A.; Smith, P. H. D.; Mortimer, S. 1997 [1997.??.??]. Habitat use and wing form in Psectra diptera (Neuroptera: Hemerobiidae). Entomologist 116:28-30.

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File: File produced for the Bibliography of the Neuropterida (BotN) component of the Global Lacewing Digital Library (GLDL) Project, 2006.