Ent. Tidskr. 138 (2017) Hymenoptera fauna on Stora Karlsö Snapshot of the Hymenopteran fauna of Stora Karlsö JULIA STIGENBERG, JOSEF BERGER, MATTIAS FORSHAGE, NIKLAS JOHANSSON, AR- TUR LARSSON, OLE LØNNVE, ALEXEY RESHCHIKOV, HEGE VÅRDAL & IKA ÖSTER- BLAD Stigenberg, J., Berger, J., Forshage, M., Johansson, N., Larsson, A., Lønnve, O., Resh- chikov, A., Vårdal, H. & Österblad, I.: Snapshot of the Hymenopteran fauna of Stora Karl- sö. [Ögonblicksbild av stekelfaunan på Stora Karlsö.] – Entomologisk Tidskrift 138 (1): 71-91. Uppsala, Sweden 2017. ISSN 0013-886x. Stora Karlsö is a small island close to Gotland in the Baltic Sea of which the Hymenopteran fauna has not been extensively studied before. In August 2014, a team of eight persons carried out an inventory of Hymenoptera, mainly the parasitoid wasps and sawflies, on the island. Sampling was done with Malaise traps for a period of 22 days, complemented with vegetation sweeping, branch shaking and opportunistic handpicking during a five day sojourn. As a result, about 200 species of parasitoid wasps and 14 sawflies are reported for Stora Karlsö for the first time. Eleven species are reported as new to Sweden: The sawfly Athalia cornubiae Benson, 1931, the gasteruptiid Gasteruption opacum (Tournier, 1877), the diapriid Spilomicrus rufitarsis(Kieffer, 1911), the eulophid Entedonomphale bulgarica Boyadzhiev & Triapitsyn, 2007, the braconids Bracon rozneri Papp, 1998 and Gnampto- don decoris (Förster, 1862), and the ichneumonids Bathythrix maculata (Hellén, 1957), Heterischnus filiformis (Gravenhorst, 1829), Lissonota picticoxis Schmiedeknecht, 1900, Mesochorus tipularius Gravenhorst, 1829, Ophion brevicornis Morley, 1915, and Plecto- chorus iwatensis (Uchida, 1928). Also the gasteruptiid Gasteruption opacum (Tournier, 1877) is reported new to Sweden based on a record from inventory by NJ in 2013. This demonstrates how the knowledge of Swedish biodiversity can be substantially augmented by a short and intensive collecting expedition. We strongly recommend that other places in the country be subjected to similar efforts. Julia Stigenberg, Mattias Forshage, Hege Vårdal, Naturhistoriska riksmuseet, Box 50007, 10405 Stockholm. E-mail: [email protected], [email protected], [email protected]. Josef Berger, Department of Biology, Lund University, Lund. E-mail: [email protected] Niklas Johansson, Aspåsen/Baskarp, 56692 Habo E-mail: [email protected] Artur Larsson, ArtDatabanken, Box 7007, 75007 Uppsala. E-mail: [email protected] Ole Lønnve, BioFokus, Gaustadalléen 21, NO-0349 Oslo, Norway. E-mail: [email protected] Alexey Reshchikov, Sun Yat-sen University, 135 Xingangxi St. Guangzhou, 510275, China. Ika Österblad, [email protected] Stora Karlsö (Fig. 1) is an island in the Baltic the west, north and northeast. The highest point Sea, belonging to Gotland both in administra- of the island is 50 m above sea-level. The island tive terms (Gotlands län & kommun) and as a consists of ca 400 million year old (Silurian) fos- faunal province. It is situated about 6 km off the sil coral reefs surrounded by layered limestone west coast of Gotland, has a subrectangular out- (Hedgren 2005, Johansson 2013). This exposed line and an area of about 2.5 km². A dominant and open alvar landscape represents a habitat feature of the landscape is a horse-shoe shaped which can be found almost exclusively in Swe- plateau forming steep cliffs along the coastline to den, on the islands of Gotland and Öland, and in 71 Julia Stigenberg et al. Ent. Tidskr. 138 (2017) Figure 1. Map of Stora Karlsö by Stellan Hedgren. The Malaise trap locations are marked M1-M6. Karta över Stora Karlsö av Stellan Hedgren. Placeringen av Malaisefällorna är markerade M1-M6. Estonia, with minor occurrences in southwest- the open areas which were once heavily grazed ern Finland (Eriksson & Rosén 2008). (Johansson 2013). For centuries, grazing kept the vegetation on A dominating shrub is the St. Lucie cherry Stora Karlsö low. Together with the geologi- (Prunus mahaleb) which is introduced and cal features, this gave rise to a unique flora and competes with the native blackthorn (Prunus fauna. When Linnaeus visited the island in July spinosa) (Johansson 2013, pers. obs.). Humans 1741, he reported that there was only one tree have been visiting the island since the stone age (an ash, which is still standing on the island) and (Hedgren 2005), and they have introduced many remarked that the grazing sheep were growing plant species (including walnut Juglans regia fat on the island (Linnaeus 1745). In 1887 graz- and sycamore Acer pseudoplatanus, though no ing was discontinued, resulting in a dramatic one as striking as the St. Lucie cherry (Broqvist change in the plant cover, with junipers (Juni- & Magntorn 1989, Johansson 2013). perus communis), pines (Pinus sylvestris) and More than for its vegetation, the island is deciduous trees spreading. In the mid-1990’s, famous for the auk colonies in the cliffs (Guil- however, the island management launched an lemot Uria aalge and Razorbill Alca torda), effort to re-create conditions favourable for or- the most important ones in the entire Baltic. In ganisms dependent on grazing (Hedgren 2005). 1970, a nature reserve was created comprising The scree areas of the island are now covered the island and its surrounding water area within by deciduous forest dominated by ash (Fraxinus 1 km distance from the shoreline. It is consid- excelsior), Norway maple (Acer platanoides), ered one of the oldest nature protection areas in elm (Ulmus glabra and U. minor), rowan (Sor- the world, because its fauna and flora have been bus aucuparia) and Swedish whitebeam (Sorbus under effective protection since 1887 when the intermedia), with ivy (Hedera helix) climbing Karlsö Association for Hunting and Conserva- the trunks and cliffs. Juniper bushes that were tion (Karlsö Jagt- och Naturskyddsförening) rare in the late 1800s can now be found on the took over management of the island (http:// entire island and form shrubberies in many of www.storakarlso.se). 72 Ent. Tidskr. 138 (2017) Hymenoptera fauna on Stora Karlsö Hymenoptera isolation from similar habitat patches and their Parasitic wasps constitute a large part of ter- size, as these can potentially contribute coloniz- restrial animal diversity everywhere, while at ers (MacArthur & Wilson 1967, Hanski 1999). the same time being poorly known and usually Highly specialised species may have difficul- neglected in inventories and conservation man- ties maintaining viable populations on islands, agement. In Sweden, they comprise roughly a as their population dynamics inevitably reflect quarter of the animal species for which the in- host population fluctuations. Within the insect formation is so scant that the Swedish popula- community, such specialists are most promi- tions cannot be judged according to the IUCN nently represented by mono- and oligophagous red-listing criteria (Gärdenfors 2000). Recent herbivores and parasitoids. Parasitoids are par- activities within the framework of the Swedish ticularly vulnerable because of their position at Taxonomy Initiative (Karlsson et al. 2005) have a high trophic level. Comparing species richness started to clarify the diversity for some groups across islands in the archipelago of southwest- of parasitic wasps within the country, whereas ern Finland, Roslin et al. (2014) found that the other groups still remain very poorly known. species-area relationship was more pronounced However, it is widely acknowledged that para- in higher trophic levels: in the sequence go- sitoid wasps play a highly important role in the ing from plants through herbivores to primary ecosystem because by ultimately killing their and secondary parasitoids, species number de- host, they contribute to population regulation of creased successively more rapidly as a function other arthropods. Also, parasitoids are recom- of shrinking area. mended as indicators in applied conservation: According to Fukami (2015), community as- Shaw & Hochberg (2001) suggest that the oc- sembly – through sequential, repeated immigra- currence of a rare species is more valuable if it, tion from the regional species pool – is influ- on a particular location, acts as host of a spe- enced on the one hand by processes for which cialised parasitoid. Unfortunately, due to lack deterministic patterns can be postulated, such as of data, protective measures for these wasps are functional traits and phylogenetic structure, and rarely taken. Most information about the biolo- on the other by the rather more random timing gy of parasitoid wasps stems from agronomy re- and order of events. Influential events may be search on potential biocontrol agents, which for abiotic, such as flood or fire, or biotic, e.g. colo- obvious reasons focuses on the most abundant nization by a species which positively or nega- species. Aculeate wasps are far better studied, tively affects the outcome of immigration by and thus well-known to be very relevant to con- another species. A species can exhibit unusual servation concerns particularly since the general abundance in the absence of otherwise signifi- public has become aware of the recent decline of cant predators, parasitoids, parasites or, perhaps honeybees. Sawflies are somewhat intermediate most importantly, when released from the in- in terms of knowledge, and mainly wood-living hibitory effect of competitors. If the organism species have been taken into consideration from communities of Stora Karlsö