The biodiversity and conservation of saproxylic Diptera in Scotland

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Over a ten year period, 1988–1998, over 300 woodlands were visited throughout Scotland and 2061 records of saproxylic Diptera obtained. Of these 1574 were ...
Journal of Insect Conservation 5: 77–85, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands.

The biodiversity and conservation of saproxylic Diptera in Scotland Graham E. Rotheray∗ , Geoff Hancock, Steve Hewitt, David Horsfield, Iain MacGowan, David Robertson & Kenneth Watt National Museums of Scotland, Chambers Street, Edinburgh EH1 1JF, UK ∗ Author for correspondence Received 14 May 1999; accepted 21 February 2000

Key words: microhabitat, breeding site, larva, rearing, specificity

Abstract Over a ten year period, 1988–1998, over 300 woodlands were visited throughout Scotland and 2061 records of saproxylic Diptera obtained. Of these 1574 were records of early stages; 258 species in 32 families were encountered; 206 species were reared of which 53 were red-listed, 9 were new to Britain and 10 were new to science. Most records came from native boreal trees such as Betula pubescens, Pinus sylvestris and Populus tremula. However, few saproxylic Diptera were specific to tree species, exceptions were 6 red-listed species associated with P. tremula and 5 red-listed species with P. sylvestris. In contrast, most saproxylic Diptera were specific to microhabitat or breeding site. The most important microhabitats were decaying sap under bark and decaying sapwood. Most red-listed species are restricted to Strathspey and north-east Scotland where relatively large stands of native boreal trees exist. Introduction Saproxylic organisms are those dependent at some stage during their life cycle, on dead wood or decaying material associated with the woody parts of trees. Saproxylic organisms vary from fungi to woodpeckers but the most biodiverse groups are Coleoptera and Diptera. In Europe saproxylic organisms often require conservation because they are under threat due to severe reduction of natural woodland and impoverishment of what remains (Speight 1989). Consequently, many redlisted species in Britain are saproxylic (Mawdsley & Stork 1995). A particularly important expression of concern is the Council of Europe’s Committee of Ministers recommendation in 1988 that EU countries protect saproxylic organisms and their biotopes (Recommendation No. R (88) 10). However, in comparison with Coleoptera, saproxylic Diptera are poorly known (Stubbs 1982). In Europe, greater attention has been paid to saproxylic Coleoptera with the result that the conservation of saproxylic Diptera is in a neglected state. For example, Jonsell et al. (1998) point out that among red-listed

saproxylic species in Sweden, Coleoptera predominate but Diptera are probably underestimated due to lack of knowledge. A particular problem is the poor state of knowledge of the breeding sites of saproxylic Diptera (Stubbs 1982). For example, although they are known to breed in exudations of sap, tree holes, under bark etc., little systematic effort has been made to determine the full range of saproxylic microhabitats used by Diptera. Furthermore, although successional stages in the decay of dead wood are well understood (Speight 1989; Stubbs 1991; Essen et al. 1992) little attempt has been made to characterise the Diptera of these stages with breeding sites frequently described in general terms such as ‘under bark’ or ‘in rotten wood’ (Teskey 1976). Finally, the extent to which saproxylic Diptera are specific to breeding sites or tree species is also poorly understood (Teskey 1976; Perry & Stubbs 1978). This paper gives the results of a ten year investigation of saproxylic Diptera mostly in Scotland. The specific aim of the fieldwork was to assess the significance for saproxylic Diptera of three qualities of dead wood, tree species, microhabitat used for breeding and geographical distribution.

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Materials and methods From 1988 to 1998 over 300 woodlands were visited throughout Scotland. They were located by reference to other entomologists, the UK government conservation agency in Scotland (Scottish Natural Heritage), ordinance survey maps and searching by car. Each visit consisted of walking slowly through the site looking for the following microhabitats: exudations of sap (= sap runs, slime fluxes), tree holes, loose bark on live trees; dead standing and fallen trees and branches; stumps; moss at the base of standing trees or growing over fallen wood. For each microhabitat the following data were recorded: microhabitat type (sap exudation, tree hole, etc.); tree species; moisture condition (wet or lying in water, damp, dry). Each microhabitat was then hand-searched for early stages using the following techniques. Sap exudations The outside of the exuded sap was first examined visually for adults and exposed larvae and puparia. Mateseeking and oviposition behaviour was noted. With the point of a knife or stick, liquid sap was searched and loose bits of bark lifted up. Care was taken to minimise damage. Tree holes The inside of the hole was first examined visually, using a torch if necessary, to look for puparia which were often above any standing water. The contents of the hole were either removed into plastic bags and searched with a knife or stick on the ground, or, if large amounts of water were present and the entrance to the hole was small, a stick was inserted and the contents stirred up. This usually dislodged any larvae which could be removed with forceps. Except for small amounts taken to rear larvae, all extracted material was replaced in the hole. Loose bark, dead standing and fallen wood and stumps The wood was approached carefully and searched visually for adults and any mate-seeking and oviposition behaviour noted. If the papery outer epidermis of the bark was soft or loose, several small (up to 10 ×10 cm2 ) areas were lifted and searched for larvae and puparia.

Similar sized pieces of entire bark were lifted and material between the bark and sapwood searched with a knife or stick. Finally, if the sapwood and heartwood were soft, several small areas per tree or branch were searched with a knife or stick. Occasionally, whole pieces of bark, dead wood, etc. were placed in 30 × 30 cm plastic bags or 250 ml plastic containers for rearing larvae in situ. In stumps and dead standing trees, wet decaying heartwood was removed from the roots and searched for larvae. It was returned to the roots after searching was finished. Moss Small areas of moss growing over fallen wood and at the base of live trees were lifted and searched for larvae and puparia both within the moss, and in the space between the moss and the wood. Larvae and puparia were reared by placing them in 25 × 75 mm corked glass tubes or 250 ml plastic tubs with small amounts of material within which they were found. They were stored in cool, dark conditions. Predators were supplied with prey, usually other larvae from the microhabitat in which they were found. Containers were checked every 2–3 weeks and water added as necessary. Adults emerging in these containers were removed to separate tubes to dry and harden. To associate adult flies with their puparia, containers were searched every 1–2 weeks and puparia removed and kept individually in separate glass tubes with a strip of moistened paper to maintain humidity and to provide a substrate for teneral adults to dry and harden. Adults were identified using standard reference works, comparison with museum specimens or sent to experts for their views.

Results Two thousand and sixty-one records of saproxylic Diptera were obtained from 22 tree genera/species (Table 1); 258 species in 32 families were encountered. Of these 1574 (76.4%) were records of early stages and 206 (79.8%) of the species recorded were reared; 53 red-listed (Shirt 1987) and notable (Falk 1991) species, 9 species new to Britain and 10 new to science were encountered (Tables 2–5). Most records (n = 208, 76.7%) came from just six tree genera/species: Betula pubescens Ehrhart, Fagus sylvatica L., Fraxinus excelsior L.,

The biodiversity and conservation of saproxylic Diptera

Pinus sylvestris Linnaeus, Populus tremula Linnaeus and Quercus (robur Linnaeus + petraea (Mattuschka) Lieblein) (Table 1). Of these B. pubescens, F. excelsior and P. sylvestris had more than 200 rearing records each (Table 1). In terms of number of species reared, B. pubescens, F. excelsior and F. sylvatica were the richest (Table 1). However, the most important tree species for red-listed Diptera were P. sylvestris B. pubescens and P. tremula followed by F. sylvatica (Table 1). Only 14 (16.4%) out of a total of 85 species with 5+ rearing records were specific to particular tree species with most associated with P. tremula and P. sylvestris (Table 6). All the remaining species were reared from two or more tree genera (Tables 2–5). All types of microhabitat occurred in all tree species sampled. However some tree species seemed more prone to acquiring particular microhabitats than others, for example: sap exudations on Aesculus hippocastanum Linnaeus; tree holes in F. sylvatica; decayed sapwood in fallen B. pubescens and, wet decaying sap under bark in fallen F. excelsior, P. sylvestris and P. tremula. Wet decaying heartrot was frequent in all trees except P. sylvestris and Quercus. Larvae of saproxylic Diptera were almost always located in damp or wet conditions in the sampled microhabitats.

Table 1. Numbers of records, species and weighted species scores of saproxylic Diptera reared from various tree species in Scotland 1988–1998. Tree species

No. records

No. species

Species score∗

Betula pubescens Fraxinus excelsior Fagus sylvatica Pinus sylvestris Quercus petraea/robur Populus tremula Ulmus glabra Acer pseudoplatanus Picea Alnus glutinosa Aesculus hippocastanum Populus Salix Sorbus aucuparia Quercus cerris Tilia europea Taxus buccata Larix Quercus borealis Prunus Abies Pseudotsuga menziesii

218 233 191 251 140 175 82 67 46 24 52 10 9 6 7 5 5 3 2 1 1 1

74 69 61 51 44 36 35 31 25 15 13 9 9 5 5 5 5 3 2 1 1 1

163 84 104 170 71 149 43 61 93 20 23 28 10 5 7 21 6 13 4 1 2 1

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Species weighted: sp. n., sp. n. to BI and RDB 1 = 16; RDB 2 = 8; RDB 3 and RDB K = 4; notable = 2; rest = 1.

Table 2. Microhabitats, numbers and associated tree species of red-listed (Shirt 1987), status categories 1–3, saproxylic Diptera obtained in 1988–1998. Family

Species

Status

No. lar./ pup.

No. sites

Tree species

Microhabitat

Ulidiidae Syrphidae Syrphidae Strongylophthalmyiidae Limoniidae Dolichopodidae Hybotidae Dolichopodidae

Homalocephala biumbrata Blera fallax Hammerschmidtia ferruginea Strongylophthalmyia ustulata Rhipida ctenophora Medetera excellens Tachypeza heeri Systenus bipartitus

RDB 1 RDB 1 RDB 1 RDB 1 RDB 2 RDB 2 RDB 2 RDB 3

20 34 50+ 3 3 28 4 2

11 4 14 2 1 26 7 3

Decaying sap Tree hole, heartrot Decaying sap Decaying sap Decaying heartrot Decaying sap Decaying sap Tree hole

RDB 3 RDB 3

15 8

12 6

RDB 3 RDB 3 RDB 3 RDB 3 RDB 3 RDB 3

3 14 5 100+ 3 18

4 14 2 32 1 18

P. tremula P. sylvestris P. tremula P. tremula A. pseudoplatanus P. sylvestris P. tremula, B. pubescens A. hippocastanum, B. pubescens P. sylvestris, Larix A. pseudoplatanus, F. sylvestris, A. hippocastanum P. sylvestris P. tremula Quercus, Picea P. sylvestris, Larix P. tremula P. sylvestris, Larix, Picea

Xylophagidae Muscidae

Xylophagus cinctus Phaonia exoleta

Asilidae Dolichopodidae Muscidae Syrphidae Hybotidae Pallopteridae

Laphria flava Medetera inpissata Phaonia laeta Callicera rufa Tachypeza truncorum Palloptera usta

Decaying sap Tree hole

Decaying wood Decaying sap Sap exudation Tree hole, heartrot Decaying heartrot Decaying sap

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G.E. Rotheray et al. Table 3. Microhabitats, numbers and associated tree species of notable category (Falk, 1991) saproxylic Diptera obtained in 1988–1998. Family

Species

Aulacigrastridae Clusiidae Clusiidae Dolichopodidae Dolichopodidae Dolichopodidae Dolichopodidae Dolichopodidae Drosophilidae Drosophilidae Empididae Empididae

Aulacigrastra leucopeza Clusiodes apicalis Clusiodes caledonica Medetera ambigua Medetera obscura Medetera petrophila∗ Medetera pinicola Systenus pallipes Chymomyza costata Stegana coleoptrata Drapetis arcuata∗ Euthyneura halidayi

Empididae Empididae Empididae Lonchaeidae Lonchaeidae Lonchaeidae Lonchaeidae Lonchaeidae Mycetobiidae

No. sites

Tree species

Microhabitat

15 50+ 50+ 1 1 0 25 50+ 15 15 0 9

19 19 10 1 2 1 28 47 l2 7 1 8

Oedalea apicalis Oedalea zetterstedti Rhamphomyia nitidula Dasiops spatiosus Lonchaea collini Lonchaea laxa Lonchaea nitens Lonchaea peregrina Mycetobia pallipes

1 0 1 2 57 1 5 12 50+

1 1 1 2 14 1 1 4 26

Sap exudation Decaying sapwood Decaying sapwood Decaying sap Decaying sap On bark Decaying sap Sap exudation Decaying sap In bark On sapwood Decaying sap, decaying sapwood Decaying sapwood Adults on bark Decaying heartwood Decaying sap Decaying sap Ex Malaise trap Decaying sap Decaying sap Sap exudation

Muscidae

Helina vicina

14

8

Rhagionidae Stratiomyidae Syrphidae Syrphidae Syrphidae Syrphidae Syrphidae Syrphidae Syrphidae Syrphidae Tipulidae Limoniidae Limoniidae Limoniidae

Ptiolina obscura Zabrachia tenella Mallota cimbiciformis Xylota coeruleiventris Xylota tarda Microdon analis Brachyopa insensilis Brachyopa pilosa Criorhina ranunculi Sphegina veracunda Tanyptera atrata f. ruficornis Limonia inusta Lipsothrix errans Gnophomyia viridipennis

6 2 1 5 20+ 15 100+ 3 3 1 2 3 1 6

7 2 1 2 14 3 49 4 3 1 2 1 1 6

Most deciduous tree species B. pubescens, P. tremula P. sylvestris P. sylvestris P. sylvestris B. pubescens P. sylvestris Most tree species Picea, P. sylvestris Acer, B. pubescens, P. tremula Acer B. pubescens, F. excelsior, P. sylvestris, P. tremula, Ulmus B. pubescens Quercus B. pubescens B. pubescens P. sylvestris, Picea F. sylvatica F. excelsior Acer, P. tremula, Quercus Acer, Alnus, Betula, Fagus Fraxinus, A. hippocastanum Betula, Fagus, Fraxinus, Pinus, Quercus, Taxus, Ulmus Acer, Quercus, Ulmus P. sylvestris F. sylvatica Picea P. tremula B. pubescens, P. sylvestris Most tree species P. tremula Acer, P. tremula P. sylvestris B. pubescens Ulmus Unknown P. tremula, Populus



No. lar./ pup.

Moss, decaying sapwood Moss, decaying sapwood Decaying sap Tree hole Decaying sap Sap exudation Ants in decaying wood Sap exudation Sap exudation Wet decaying heartwood Decaying sap Decaying sapwood Moss, decaying sapwood Decaying sapwood Decaying sap

not breeding in dead wood.

Most records (n = 1025, 67.8%) and species (n = 175, 65.1%) came from decaying sap under bark and decaying sapwood in fallen wood. Wet decaying sap under bark was only present in fallen wood up to about four years old. After this time it dried out. Sap exudations were the next richest microhabitat with 282 records (17.9%) and 33 species (12.7%). Tree holes were the least rich microhabitat with 121 records (7.6%) and 19 species (7.3%). Of 85 species with 5+ rearing records, only 18 (21.1%) were reared from more than one microhabitat of which 6 were red-listed species (Tables 1–4). However, the number of species

utilising two or more microhabitats is actually less than these figures indicate. Some species found as puparia in moss actually developed in decayed sapwood and moved into the moss to pupate. Moss was not essential however, because at other times puparia of these species were found near cracks or loose bark. Furthermore, some species, like Blera fallax (Linnaeus) and Callicera rufa Schummel (Syrphidae) were recorded from pine stumps with either wet decaying heartrot in the roots or wet decaying heartwood in holes at the surface of the stump. Thus the numbers using more than one microhabitat may be even less. In terms of

The biodiversity and conservation of saproxylic Diptera

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Table 4. Microhabitats, numbers and associated tree species of saproxylic Diptera new to Britain obtained in 1988–1998. Family

Name

No. lar./ pup.

No. of sites

Tree species

Microhabitat

Mycetobiidae Mycetobiidae Dolichopodidae Lonchaeidae Lonchaeidae Lonchaeidae Lonchaeidae Lonchaeidae Calliphoridae

Mycetobia gemella Mamaev∗ Mycetobia obscura Mamaev∗ Medetera fasciata Frey Lonchaea affinis Lonchaea caucasica Kovalev Lonchaea hackmani Kovalev Lonchaea ragnari Hackman Lonchaea zetterstedti Becker Bellardia bayeri (Jacentkovsky)∗∗

44 14 2 0 4 17 21 13 2

2 1 4 2 2 5 5 5 3

P. sylvestris P. tremula P. sylvestris B. pubescens B. pubescens P. tremula B. pubescens Picea, P. sylvestris F. sylvatica

Tree hole Sap exudation Decaying sap Unknown Decaying sap wood Decaying sap Decaying sap wood Decaying sap Decaying sap



Hancock et al. (1996); ∗∗ Rotheray et al. (1998).

Table 5. Microhabitats, numbers and associated tree species of saproxylic Diptera new to science obtained in 1988–1998. Family

Name

No. lar./ pup.

Mycetophilidae Psychodidae Scatopsidae Dolichopodidae

Creagdhubhia mallochorum∗ Philosepedon sp. Ectaetia christii∗∗ Systenus mallochi∗∗∗

0 5+ 80+ 2

1 1 2 2

Odiniidae Pallopteridae

Odinia sp. Palloptera anderssoni∗∗∗∗

0 23

1 7

Lonchaeidae Lonchaeidae Lonchaeidae Lonchaeidae

Lonchaea sp. 1 Lonchaea sp. 2 Lonchaea sp. 3 Lonchaea sp. 4

14 47 6 10

5 20 2 7



No. of sites

Tree species

Microhabitat

P. sylvestris P. sylvestris P. tremula A. pseudoplatanus, B. pubescens, Quercus B. pubescens A. pseudoplatanus, B. pubescens, F. sylvatica, Populus, Tilia europea F. excelsior Most tree species F. sylvatica, Salix P. sylvestris

Decaying sap Sap exudation Decaying sap Tree hole Adults on fungus Decaying sap

Decaying sap Decaying sap Decaying sap Decaying sap

Chandler (1999); ∗∗ Rotheray and Horsfield (1997); ∗∗∗ MacGowan (1997); ∗∗∗∗ Rotheray and MacGowan (1999).

red-listed species, all microhabitats were utilised but the most important microhabitat was decaying sap under bark, followed by decaying sapwood and sap exudations (Table 7). Most red-listed species associated with P. sylvestris and P. tremula came from Strathspey and sites in the north-east of Scotland. Although P. sylvestris and P. tremula are widely distributed throughout Scotland, the largest natural stands of these trees were in Strathspey and the north-east. Red-listed species associated with B. pubescens had a wider distribution including central Scotland and extending as far south as Midlothian. Species associated with F. sylvatica and F. excelsior tended to be more common in the centre and south of Scotland where these trees are more abundant.

Discussion We reared 258 species of saproxylic Diptera of which 71 were red-listed, new to Britain or new to science.

This contrasts with 46 red-listed Diptera species considered by Jonsell et al. (1998) in Sweden and suggests that these authors were correct to suggest that saproxylic Diptera are generally underestimated in studies of dead wood. There was wide variation in the number of saproxylic Diptera reared from different tree species (Table 1). Most records and species came from northern boreal trees such as B. pubescens, P. sylvestris and P. tremula. However tree species such as F. sylvatica and F. excelsior, also scored well. In Scandinavia, Jonsell et al. (1998) found Quercus to be the most speciesrich tree genus for saproxylic invertebrates, but they may have over-emphasised Coleoptera which are particularly associated with this tree genus. Our results for saproxylic Diptera in Scotland, reveal that Quercus is not so important (Table 1). To conserve saproxylic Diptera in Scotland, emphasis should be given to tree species like B. pubescens, P. sylvestris, F. excelsior and P. tremula. However, little evidence was obtained of saproxylic Diptera being specific to tree species or genus. Most

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G.E. Rotheray et al. Table 6. Red-listed, notable, species new to Britain and species new to science of saproxylic Diptera reared 5+ times from one tree species. Species

Family

Status

Tree species

Ulidiidae Syrphidae Syrphidae Dolichopodidae Dolichopodidae Clusiidae Dolichopodidae Syrphidae Psychodidae Scatopsidae Lonchaeidae Lonchaeidae Lonchaeidae Lonchaeidae

Homalocephala biumbrata Blera fallax Hammerschmidtia ferruginea Medetera excellens Medetera inpissata Clusiodes caledonica Medetera pinicola Xylota tarda Philosepedon sp. Ectaetia christii Lonchaea sp. 1 Lonchaea hackmani Kovalev Lonchaea nitens Lonchaea ragnari Hackman

RDB 1 RDB 1 RDB 1 RDB 2 RDB 3 notable notable notable sp. n. sp. n. sp.n. sp. n. to Britain notable sp. n. to Britain

P. tremula P. sylvestris P. tremula P. sylvestris P. tremula P. sylvestris P. sylvestris P. tremula P. sylvestris P. tremula F. excelsior P. tremula F. excelsior B. pubescens

Table 7. Red-listed, notable, species new to Britain and species new to science of saproxylic Diptera reared according to microhabitat. Status RDB 1 RDB 2 RDB 3 notable sp. n. n. to BI Total

Sap run

l 6 1 1 9

Under bark 3 2 3 15 7 7 37

Decayed sapwood

Decaying heartrot

Moss

9

1 1 1 2

3

9

5

3

Rot hole

2 1 1 1 5

of the 14 species showing specificity were associated with P. sylvestris and P. tremula and were red-listed, new to Britain or new to science (Table 6). In contrast, nearly a third of saproxylic invertebrates in Sweden show evidence of specificity (Jonsell et al. 1998). Additional rearing records are needed among the saproxylic Diptera we reared infrequently (< 5 records), to see whether we have underestimated specificity. There was better evidence for microhabitat specificity. Most species reared 5+ times, came from one microhabitat (Tables 1–4). This suggests that ovipositing females orientate to cues emanating from particular states of decay in microhabitats rather than to cues from trees themselves. Although we reared red-listed species from all microhabitats investigated, most species came from decaying sap under bark and decaying sapwood (Table 7). Both these microhabitats occur as natural stages in the decay of fallen wood and tree stumps (Essen et al. 1992). When a tree or branch first falls or is cut, the cambium and inner cortex of the bark decay over about 12–15 months and form a wet layer

under the bark. This lasts for about three years in which the decaying bark separates slowly from the sapwood, cracks and incoming air dries out the wet decay. At any one site, fresh imputs of fallen or cut wood are needed every 1–3 years to ensure sufficient microhabitat is available to those Diptera dependent on it for breeding. Imputs of fallen or cut wood are also needed to keep up the supply of soft decayed sapwood. However, if the bark is reasonably intact, it takes up to ten years for sapwood to decay into the soil and thus, the requirement for resupply is not so urgent. All three qualities of dead wood examined, tree species, microhabitat and geographical distribution, are required to assess the biodiversity and conservation needs of saproxylic Diptera. Combining data on these qualities the most important situations for red-listed Diptera in Scotland are fallen trees and branches and stumps of B. pubescens, P. sylvestris and P. tremula in Perthshire, Strathspey and the north-east of Scotland where 84% of the fauna occurred (Tables 2–5). Of the few remaining red-listed species, most have centres of population further south in Britain and are not part of the boreal or hemiboreal zone. Many of the red-listed species we reared and the saproxylic microhabitats we sampled are considered to be rare and difficult to find (Stubbs 1982; Speight 1989). We found that by concentrating effort on breeding sites and early stages, data on saproxylic Diptera were readily acquired. For example, we investigated the status of Callicera rufa (Syrphidae) by searching for early stages in the microhabitat used for breeding, rot holes in pine trees and stumps, rather than on the elusive adult (Rotheray & MacGowan 1990). The results showed that C. rufa was widely distributed in

The biodiversity and conservation of saproxylic Diptera Scotland enabling Falk (1991) to revise its RDB status from category 1 (endangered) to category 3 (rare). We now have enough records to revise the status of this species even further to notable (Table 8). Such revisions enable scarce resources for conservation to be accurately targeted. Looking for larvae has other advantages. Microhabitats can be sampled at any time because many larvae have growth periods of more than a year and they are used repeatedly by succeeding generations. This makes long-term monitoring of populations a feasible prospect and recognition of particular trees with such microhabitats, a simple means of conserving them. Re-evaluations of status are possible with our data. For example, the British status of 9 red-listed species should be revised and the red-list status of 9 species new to Britain and 10 species new to science can be worked out (Table 8). Furthermore, our data on the syrphids, Hammerschmidtia ferruginea (Fall´en) and B. fallax confirmed them in their endangered categories and provided one of the justifications for these

species to be included in the British Government Biodiversity Action Plan process. These will be ‘flagship’ species: by conserving them, other red-listed species will also benefit. For example, H. ferruginea only breeds in exuding and decaying sap of P. tremula and shares this habitat with over 12 other red-listed species (MacGowan 1993). Our data suggest that the advice for conserving saproxylic insects given in Fry and Lonsdale (1991), Kirby and Drake (1993) and Read (1991) may work for Coleoptera but is only partially effective for Scottish Diptera. For example, in contrast to Coleoptera, the majority of saproxylic Diptera need measures to conserve wet microhabitats for breeding. Coleoptera frequently require veteran (large, old) trees. Although veteran trees often have more wet microhabitats than young trees, they are not essential for saproxylic Diptera. We repeatedly found red-listed saproxylic Diptera breeding in small, young trees. Also, because of the high relative abundance of trees like Acer pseudoplatanus L. and F. sylvatica in Scotland, they

Table 8. Re-evaluations of status of red-listed saproxylic Diptera, and proposed status categories for species new to Britain and species new to science based on definitions of categories in Falk (1991) and records obtained in 1988–1999. Family

Species

Status

Evaluation∗

Dolichopodidae Syrphidae Pallopteridae Mycetobiidae Dolichopodidae Dolichopodidae Syrphidae Aulacigastridae Clusiidae Mycetobiidae Mycetobiidae Dolichopodidae Lonchaeidae Lonchaeidae Lonchaeidae Lonchaeidae Calliphoridae Mycetophilidae Psychodidae Scatopsidae Dolichopodidae Odiniidae Pallopteridae Lonchaeidae Lonchaeidae Lonchaeidae Lonchaeidae

Medetera excellens Callicern rufa Palloptera usta Mycetobia pallipes Medetera pinicola Systenus pallipes Brachyopa insensilis Aulacigastra leucopeza Clusiodes apicalis Mycetobia gemella Mycetobia obscura Medetera fasciata Lonchaea caucasica Lonchaea hackmani Lonchaea ragnari Lonchaea zetterstedti Bellardia bayeri Gnonstinae sp. Philosepedon sp. Ectaetia christii Systenus mallochi Odinia sp. Palloptera anderssoni Lonchaea sp. 1 Lonchaea sp. 2 Lonchaea sp. 3 Lonchaea sp. 4

RDB 2 RDB 3 RDB 3 notable notable notable notable notable notable sp. n. BI sp. n. BI sp. n. BI sp. n. BI sp. n. BI sp. n. BI sp. n. BI sp. n. BI sp n. sp. n. sp. n. sp. n. sp. n. sp. n sp. n. sp. n. sp. n. sp. n.

RDB 3 notable notable Remove from list Remove from list Remove from list Remove from list Remove from list Remove from list RDB 3 RDB K RDB 2 RDB 2 RDB 2 RDB 3 RDB 3 RDB K RDB K RDB K RDB 1 RDB 2 RDB K RDB 2 RDB 2 notable RDB K RDB 2



Rarity category definitions follow Falk (1991).

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are of value for saproxylic Diptera (Table 1). Consequently, habitat restoration schemes involving the removal of such trees should be partial and spread over 10 or more years to allow the fauna to adjust. These features show the importance of recognising that different groups have different needs in different places. In Scotland many species are at the edge of their range and suitable habitat tends to be patchy in occurrence. As a result, populations are fragmented and isolated. For example, the notable hoverfly, Brachyopa pilosa Collin (Syrphidae) is scarce but fairly widespread in southern Britain up to Northamptonshire and Warwickshire (Falk 1991 and pers. comm.). The only populations north of this point are in the Moray and Cromarty Firth areas of north-east Scotland. Isolated populations of Scottish butterflies have often evolved into distinctive races and forms (Thomson 1980). This appears to have occurred with B. pilosa. Unlike southern populations which breed in association with Fagus, Quercus and Populus, Scottish B. pilosa appears to be specific to P. tremula (Rotheray 1996). The extent to which populations of other Scottish saproxylic Diptera have evolved races and forms is unknown. Most of the species we discovered new to science and some that were new to Britain apparently form a sister group relationship with a widespread species under which they had been confused. When the distributions of the two sister species were defined a northern, boreal species and a southern species emerge. For example, we discovered a new species, Ectaetia christii Rotheray and Horsfield (Scatopsidae) breeding in wet decaying sap under bark of P. tremula in Strathspey (Rotheray & Horsfield 1997). This species is most similar to the widespread southern species, Ectaetia clavipes (Loew). Similarly, the lonchaeid, Lonchaea hackmani Kovalev (Lonchaeidae) which we found new to Britain in north-east Scotland (Table 6) was recognised as separate from the closely-related species, Lonchaea peregrina Becker (Kovalev 1981). Specimens previously identified as L. peregrina from northern Europe turned out to be the new species, hackmani with peregrina being confined to the south (Kovalev 1981). The extent to which the biodiversity of the boreal zone in Europe is underestimated by species like these has yet to be determined.

Acknowledgements We are grateful to all the landowners and managers for permission to examine woodlands in their care

and to the numerous collaborating entomologists who have helped this project in various ways, particularly Alan Stubbs, Peter Chandler, Ivan Perry, Roy Crossley, David Phillips and John Ismay. We are also grateful for the help provided by other members of the Malloch Society towards our work on saproxylic Diptera, particularly Richard Lyszkowski. Financial assistance was provided to the Malloch Society for this project by the British Ecological Society, the Worldwide Fund for Nature (UK) and Scottish Natural Heritage.

References Chandler, P.J. (1999) Creagdhubhia mallochorum gen. and sp. n. (Diptera: Mycetophilidae), a remarkable new Scottish gnat with a discussion of its relationships. British Jounal of Entomology and Natural History 12, 121–34. Essen, P.A, Ehnstrom, B., Ericson, L. and Sjoberg, K. (1992) Boreal forests, the focal habitats of Fennoscandia. In Ecological principles of nature conservation, pp. 252–325 (L. Hansson, ed). London and New York: Elsevier. Falk, S.J. (1991) A review of the scarce and threatened flies of great Britain. Research and Survey in Nature Conservation 39, 1–194. Fry, R. and Lonsdale, D. (eds) (1991) Habitat conservation for insects – a neglected green issue. The amateur entomologist, vol 21, 262 pp. Hancock, E.G., Robertson, D.M. and MacGowan, I. (1996) Saproxylic Diptera in Scotland 1. Additions to the British fauna of Mycetobia (Diptera, Mycetobiidae). Dipterists Digest 3, 32–5. Jonsell, M., Weslien, J. and Ehnstrom, B. (1998) Substrate requirements of red-listed invertebrates in Sweden. Biodiversity and Conservation 7, 749–64. Kirby, P. and Drake, C.M. (1993) Dead wood matters: the ecology and conservation of saproxylic invertebrates. English Nature Science, No. 7. Kovalev, V.G. (1981) On European species of the group Lonchaea peregrina (Diptera, Lonchaeidae). Zoologicheskii Zhural 60, 221–8. MacGowan, I. (1993) The Entomological value of Aspen in the Scottish Highlands. Malloch Society Research Report No. 1, 43 pp. MacGowan, I. (1997) Systenus mallochi sp. n. from Britain (Diptera, Dolichopodidae). Dipterists Digest 4, 24–9. Mawdsley, N.A. and Stork, N.E. (1995) Species extinctions in insects: ecological and biogeographical considerations. In Insects in a changing environment (R. Harrington and N.E. Stork, eds), pp. 321–69. Perry, I. and Stubbs, A.E. (1978) Dead wood and sap runs. In A Dipterist’s handhook. The amateur entomologist. (A.E Stubbs and P. Chandler, eds), vol 15, pp. 65–73. Read, H.J. (ed) (1991) Pollard and veteran tree management. Corporation of London. Rotheray, G.E. (1996) The larva of Brachyopa scutellaris RobineauDesvoidy (Diptera: Syrphidae) with a key to and notes on the larvae of British Brachyopa species. Entomologist’s Gazette 47, 199–205.

The biodiversity and conservation of saproxylic Diptera Rotheray, G.E. and Horsfield, D. (1997) Ectaetia christii sp. n., a Scottish species similar to Ectaetia clavipes (Diptera, Scatopsidae). Dipterists Digest 4, 41–4. Rotheray, G.E. and MacGowan, I. (1990) Re-evaluation of the status of Callicera rufa Schummel (Diptera: Syrphidae) in the British Isles. The Entomologist 109, 35–42. Rotheray, G.E. and MacGowan, I. (1999) Palloptera anderssoni sp. n. from Scotland and Finland (Diptera: Pallopteridae). British Journal of Entomology and Natural History 11, 175–9. Rotheray, G.E., Horsfield, D., Ismay, J.W. and Chandler, P.J. (1998) Bellardia bayeri (Diptera, Calliphoridae) new to Britain and a description of the puparium. Dipterists Digest 5, 30–33. Shirt, D.B. (1987) British red data books: 2. Insects. Peterborough: Nature Conservancy Council.

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Speight, M.C.D. (1989) Saproxylic invertebrates and their conservation. Nature and Environment Series, No.42. Strasbourg: Council of Europe. Stubbs, A.E. (1982) Hoverflies as primary woodland indicators with reference to Warncliffe Wood. Sorby Record 20, 62–7. Stubbs, A.E. (1991) Insects in dead wood in standing and fallen trees, pp. 58–67. In Habitat conservation for insects – a neglected green issue. The amateur entomologist, (R. Fry, and D. Lonsdale, eds), vol 21. Teskey, H.J. (1976) Diptera larvae associated with trees in North America. Memoirs of the Entomological Society of Canada 100, 1–53. Thomson, G. (1980) The butterflies of Scotland. London: Croom Helm.