Kopi fra DBC Webarkiv Kopi af: Species diversity, distribution, and conservation status of the Asilidae (Insecta: Diptera) in Denmark Dette materiale er lagret i henhold til aftale mellem DBC og udgiveren. www.dbc.dk e-mail: [email protected] CONSERVATION STATUS OF DANISH ASILIDAE (DIPTERA) 177 Species diversity, distribution, and conservation status of the Asilidae (Insecta: Diptera) in Denmark MARIE NYKJÆR LARSEN & RUDOLF MEIER Steenstrupia Larsen, M. N. & R. Meier. Species diversity, distribution, and conservation status of the Asilidae (Insecta: Diptera) in Denmark. – Steenstrupia 28 (2): 177–241. Copenhagen, Denmark, December 2004 (for 2002). ISSN 0375-2909. We report the results of the second atlas study for Danish Diptera. It covers the 30 confirmed species of Danish Asilidae and is based on label data from more than 4300 museum specimens. For each species we provide a distribution map and discuss its distribution, phenology, and conservation status in Denmark. We furthermore present a new identification key that not only includes the known Danish species, but also those likely to occur in Denmark based on their presence in surrounding countries. It is shown that the distributional data suffers from the kind of spatial and temporal collecting bias that is commonly observed in museum samples. Several techniques are used to remove the bias before the information is used for proposing a Red List for the Danish Asilidae. This proposal is one of the first for insects that applies the quantitative criteria of the World Conservation Union (IUCN 2001). One species is found to be Data Deficient (DD: Tolmerus cingulatus); one species is Regionally Extinct (EX: Molobratia teutonus); five species are found to be Critically Endangered (CR: Antipalus varipes, Cyrtopogon lateralis, Machimus arthriticus, Machimus gonatistes, Neoitamus cothurnatus); two species are Endangered (EN: Eutolmus rufibarbis, Laphria ephippium); three species are Vulnerable (VU: Asilus crabroniformis, Leptarthrus brevirostris, Rhadiurgus variabilis); two species are classified as Near Threatened (NT: Choerades gilvus; Dioctria cothurnata ); and the remaining 16 species are Least Concern (LC). Three species have not been collected since 1960 and for five additional species there are fewer than 5 post-1960 records. We urge that the old localities be revisited in order to elucidate whether the species might have become extinct. An investigation into the distribution and status of the “Danish” species of Asilidae in other European countries reveals that all “Danish” species are widespread and Denmark is geographically near their Northern distribution limit. For many of the species on the Danish Red List a decline has also been observed in other industrialized countries like Belgium and the Netherlands, and in at least one case (Asilus crabroniformis) natural history evidence implies that modern agricultural practices are at least partially to blame. It is discussed why Asilidae might be one of the few Diptera taxa of interest to conservation biology. Keywords: Robber flies, identification key, museum data, collecting bias, distribution maps, conservation status, Red List. Marie Nykjær Larsen & Rudolf Meier: Zoological Museum, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen Ø, Denmark. Present addresses: MNL: Ordrup Jagtvej 54B, DK-2920 Charlottenlund, Denmark. E-mail: [email protected] RM: Department of Biological Science, National University of Singapore, 14 Science Drive 4, Singapore 117543. E-mail: [email protected] INTRODUCTION able and locality information has either already been collected (see appendix 2 in Lund & Rahbek Recent decades have seen an increasing interest 2000) or is being gathered at a quick pace by in the conservation of the Danish fauna and flora projects like the Danish mammal-atlas project (e.g., Ministry of Environment and Energy 1996, (Baagoe & Jensen 2000). The situation is less Lund & Rahbek 2000). However, precondition satisfactory for the generally much more speciose for conserving taxa is detailed information on the arthropod groups, which comprise most of the diversity and distribution of species. For many Danish species diversity. Fortunately, for three of vertebrate groups accurate species lists are avail- the four megadiverse insect orders species cata- Steenstrupia 28(2): 177–241. 178 M. N. LARSEN & R. MEIER logues for Denmark have been assembled through specimen recording schemes like the one (Coleoptera: Hansen 1996; Lepidoptera: Kars- presented here that they become available. It is holt & Nielsen 1998; Diptera: Petersen & Meier thus not surprising that only two country-wide 2001), but distribution maps and/or locality lists Red Lists (Sweden, Finland) have attempted to are restricted to very few taxa (listed in appendix consistently use the IUCN criteria for inverte- 3 of Lund & Rahbek 2000). For example, within brates (Gärdenfors 2001). the Diptera, which comprise an estimated 20% of The Asilidae is a diverse family within the the Danish species diversity (Petersen & Meier Diptera. So far more than 6800 species have been 2001), maps exist only for the Syrphidae (Torp described, but new species are constantly being 1994). found (Geller-Grimm 2000). The robber flies are We here provide locality lists and maps for a most diverse in warm and arid regions, with spe- second group, the Asilidae – robber flies. The cies numbers rapidly decreasing toward the trop- information is based on more than 4300 speci- ics and the temperate regions (Lyneborg 1965). mens from the main collections of Danish insects Denmark has few species (30–37 species; see (Zoological Museum, University of Copenhagen; Petersen et al. 2001) because it is close to the Museum of Natural History, Aarhus) and from northern limit of the asilids’ range. Adult Asilidae the private collection of R. Bygebjerg. Our study prey on other insects and spiders (Wood 1981). augments Lyneborg’s (1965) important treatment This predaceous mode of life is reflected in the of the Danish Asilidae, which is the main refer- distinctive morphology of the adults, which can ence for natural-history information and for mor- be used to identify the family (see Lyneborg 1965 phological descriptions of the immature and adult for detailed diagnosis). Especially conspicuous stages. However, Lyneborg’s study only indi- are the eyes, which are separated by the sunken cates species distributions in a narrative form, vertex (Fig. 7) and provide forward- and back- while we here provide detailed distribution maps, ward- as well as stereoscopic vision. When prey is detailed lists of localities for all species, and detected it is seized by the legs, which are unusu- discuss abundance changes over time. We also ally long, robust and usually covered with bristles incorporate information from more than 1000 and hairs. As diagnostic for the family as the eyes specimens that were collected after 1965 and is the so-called mystax, which consists of hairs update Lyneborg’s species key by including mor- and bristles that are found in the middle of the phological characters from the recent literature face and are thought to protect the eyes from (e.g., Weinberg & Bächli 1995, Geller-Grimm & struggling prey (Figs 4, 12). The mystax extends Smart 1998). This new key not only covers the in some cases to the antennal bases (Wood 1981) species confirmed as belonging to the Danish and is often found on a protuberance (Fig. 12). fauna, but also those that might occur here based The victims of Asilidae are mostly insects, which on their presence in neighboring countries (Pe- are paralyzed by a neurotoxin injected through tersen et al. 2001). the hypopharynx. The liquefied content of the The detailed information on the distribution victim is then imbibed through the proboscis of and abundance of Asilidae is then used to propose the predator (Geller-Grimm 2000). a Red List. Ideally, such lists should be based on The phenology of the Asilidae in general is the official criteria by the World Conservation poorly known (Lyneborg 1965). Information Union (IUCN 2001), but until recently there were about the early immature stages exists only for 16 two obstacles for cases like the Danish Asilidae. species (Musso 1981) and complete life-cycle (1) The criteria were only intended for use on the descriptions are restricted to four species: Pro- global scale and it was not until recently that they machus yesonicus Bigot, 1887, Mallophora have been modified to fit the needs of regional ruficauda (Wiedemann, 1828), Mallophora me- lists (Gärdenfors 2001, Gärdenfors et al. 2001). dia Clements & Bennett, 1969, and Machimus (2) The IUCN criteria require quantitative state- rusticus (Meigen, 1820) (Musso 1978). Machi- ments about the abundance, distribution, and/or mus rusticus is the only Palaearctic species probability of extinction for each species. Such among those and is probably for now the best data are usually not available for insects. It is only model for Danish Asilidae. Under laboratory CONSERVATION STATUS OF DANISH ASILIDAE (DIPTERA) 179 conditions Musso (1978) found that the eggs of (Enghoff & Nielsen 1977, Madsen 1999) based M. rusticus hatch after 4–6 days, which is also the on “Det levende Danmarkskort” (Kort & Ma- time required for the eggs of most other asilid trikelstyrelsen 2000). When the name of a locality species. One known exception is Andrenosoma corresponded to multiple places in Denmark or a atra (Linnaeus, 1758), which requires 50–56 locality was neither found in “Det levende Dan- days. The duration