﻿Identification key to and checklist of the Swedish Phlaeothripidae (Thysanoptera)

﻿Abstract The Swedish fauna of thrips (Thysanoptera) in the family Phlaeothripidae consists of 49 species. A key to the species of Phlaeothripidae found in Sweden is provided. One species is recorded as new for the country, and 10 new regional records are presented. A checklist of all Swedish tubuliferan species with regional distributions is also given.


Introduction
Thysanoptera Haliday, 1836, more commonly known as thrips, are minute insects which are often not longer than 3 mm; larger species may reach 5 mm in size. Thrips have caught attention not only from researchers but also from the commercial and private sector, due to their impact as pests in agriculture (Paine 1992) and even as invasive species (Held et al. 2005;Boyd and Held 2006). The group least studied in Sweden is the family Phlaeothripidae Uzel, 1895. Some species are found in flowers, e.g., in the genus Haplothrips Amyot & Serville, 1843 ( Fig. 1), but most of the known species in Sweden are found in soil, leaf litter, and decaying wood.
The research regarding Palaearctic taxa is scarce. Only a few regional checklists have been published in recent years, and the most relevant identification keys focus on the species in Great Britain (Mound et al. 1976(Mound et al. , 2018Kirk 1996). In recent years the fauna of Poland, a region with a previously similarly understudied thrips fauna, has been studied more extensively, which has led to a large gain in both taxonomic and ecological knowledge (Kucharczyk and Zawirska 1994;Kąkol and Kucharczyk 2004;Kucharczyk 2004;Kucharczyk and Kucharczyk 2008;Dubovský et al. 2010;Kucharczyk and Wyrozumski 2015). Most of the knowledge of Swedish taxa is based on older identification literature, e.g., Ahlberg (1926), Mound et al. (1976), and Kirk (1996), often not specific for Scandinavian conditions. A few papers have been published reporting new species at irregular intervals, reporting sporadic observations (Qvick 1977;Vasiliu-Oromulu et al. 2000;Kobro 2011;Sörensson 2012;Gertsson 2015a;Gertsson and Fägerström 2017). Kobro and Rafoss (2006) produced a key to the genus Hoplothrips in Norway, and Kobro (2013) produced an identification key to Norwegian thrips in general but only covered the most common and for amateurs easily distinguished species. The overlaps of the distributions the of Swedish and Norwegian species is currently not known, and no identification key to the Swedish fauna exists. Gertsson (2015b) provided a checklist of Nordic thrips. However, this was based only on previously collected specimens in museum collections. Recently new records to the fauna were made from freshly collected material, with a total of 5 new species for Sweden and several new regional records (Gertsson and Fägerström 2017;Gertsson 2021;Gertsson et al. 2022). In this paper we update the Swedish checklist of the family Phlaeothripidae and provide an identification key to the species with photographic illustrations.

Material and methods
For this study we have examined representative specimens from the collections of The Swedish Museum of Natural History, Sweden (NHRS), Lund Museum of Zoology (MZLU), Sweden, Forschungsinstitut und Naturmuseum Senckenberg (SMF), Germany, and the private collections of Sverre Kobro and Manfred R. Ulitzka. In addition, newly collected material has been used, prepared on slides with Euparal according to the method outlined in Kobro (2013). The exception to this method is the preservation prior to maceration and the maceration step, where in this study fresh material has been stored in 80% ethanol prior to DNA extraction. Maceration has thereafter been carried out during DNA extraction before preparation on microscopic slides. This method has successfully been used for one-step DNA extraction and maceration for small insect specimens (Wahlberg and Johanson 2018;Wahlberg 2019). DNA extract is stored at the NHRS for further studies. The material was examined and photographed using manual focus stacking on Nikon Eclipse 80i and Swift 380T microscopes, with Nikon DS-Fi1 and Swift SC1003 cameras. Photos were automatically aligned and stacked using Helicon Focus 8.0.4 and Swift Imaging 3.0, and edited and finalized in Adobe Photoshop CC 23.2.0. The distributional data are provided on county level. The material collected and preserved during this project is deposited at the NHRS.

Swedish faunistic provinces and abbreviations
Sweden is traditionally divided in to faunistic provinces, most based on historical cultural regions overlapping with administrative counties (Fig. 2). They are in the checklist and map abbreviated as below, from south to north. Torne lappmark

Characters
The identification key is intended to be used for adult specimens, both females and males in various life stages and both winged and micropterous forms. For this reason, some species that express great intraspecific variation it is possible to find one species at several locations in the key (indicated by "[part]"). In Thysanoptera the most important morphological characters for species identification include antennal shape, presence, shape, and length of setae, structure of mouth parts, and measurements of segments (Fig. 3). This always requires high magnification and specimen preparation. Large setae may be blunt, expanded (Fig. 10G), or acute at apex, and care need to be taken in preparation for avoiding collapse of expanded apices. The antennal segments often carry sensory organs in the shape of large trichomes, sense cones. These are more robust and broader than bristles that they might be confused with ( Fig. 6A-C). Maxillary stylets are parts of the feeding apparatus and can be seen in macerated specimens (Fig. 4A, B), and the width and distance of the stylets and presence or absence of the median extension called maxillary bridge are used for separation of subfamilies and species groups. The last abdominal segment, segment X, may be either tapering and longitudinally divided (in most of the Thysanoptera families) or complete and tube-shaped. The latter being one of the defining characters of the family Phlaeothripidae ( Fig. 3) and is in the key only referred to as the tube. Comprehensive and detailed descriptions of the anatomy and morphology of Thysanoptera are provided in Schliephake and Klimt (1979) and Moritz (2006).

Distribution. Go.
Remarks. First record for Sweden. In Fennoscandia this species has previously been recorded from Denmark, Norway, and Finland (Kobro 2011;Gertsson 2015b). Feeding on fungal spores (Mound 1974), and found in dry grass, sedges, and on dead branches mainly from Salix L. (Mound et al. 1976;Schliephake and Klimt 1979).
Notes. The majority of phlaeothripids belongs to this subfamily; from Sweden 42 species are known. The life histories are very varying, ranging from species feeding on fungal hyphae to predatory species (Mound and Tree 2020).

Cephalothrips Uzel, 1895
Cephalothrips monilicornis (Reuter, 1880) Fig. 9C Distribution. Sk, Vg, Öl, Sm, Sö, Up, Vr.        Remarks. This species is variable in the number of sense cones on both antennal segments III and IV, as well as in number of large pronotal seatae. Fig. 11D Distribution. Sk, Ha, Up. Remarks. First record for Ha. Very variable in the number of sense cones on both antennal segments III and IV, as well as many structural differences in macropterous and apterous males and females.