A key to the second instar larvae of the Thripidae of the Western Palaearctic region (Thysanoptera) G. (Bert) Vierbergen, Halina Kucharczyk & William D. J. Kirk A key to the second instar larvae of 130 species of Thripidae occurring in the Western Palaearctic Region is presented, covering 40% of the total number of Thripidae species from that region. Additionally some species of quarantine interest are included in the key: Scirtothrips aurantii Faure, S. citri Moulton, S. dorsalis Hood, Selenothrips rubrocinctus (Giard), Stenchaetothrips spinalis Reyes, Taeniothrips eucharii (Whetzel) and Thrips parvispinus Karny. Sampling and preparation techniques of second instar larvae of Thysanoptera are given. In contrast with adults, second instar larvae provide reliable distribution and host plant data for species. Additionally, larvae are often encountered during import inspections of plant products and their identification enhances the efficiency of quarantine measures for harmful species. G. (Bert) Vierbergen*, Department of Entomology, Reference Laboratory for Phytosanitary Diagnostics, Plant Protection Service, 6700 HC Wageningen, P.O. Box 9102, The Netherlands. [email protected] Halina Kucharczyk, Department of Zoology, Maria Curie-Skłodowska University, Akademicka 19 Str., 20–033 Lublin, Poland. [email protected] William D. J. Kirk, School of Life Sciences, Keele University, Staffordshire ST5 5BG, U.K. [email protected] Introduction quiescent immature stages, known as propupa, pupa When studying Thysanoptera, specimens of the I and pupa II. The third quiescent stage, pupa II, adult stage are most commonly encountered. Iden- occurs only in the family Phlaeothripidae. Although tification keys to the nearly 6000 described species, Thysanoptera are exopterygote, having wing pads in based on morphological features of these adults, are the quiescent stages, there is extensive replacement of available for several regions of the world, for example juvenile structures with adult structures during the a key to the species of Europe and the Mediterranean quiescent stages. This means that they are effectively Area (Zur Strassen 2003). There are also several keys holometabolous and so it is appropriate to use the to the pest species of the world (Palmer et al. 1989, terms “larva” and “pupa” for the immature stages, Mound & Kibby 1998, Moritz et al. 2001). How- rather than the term “nymph” (Nüesch 1987, Rich- ever, when studying subjects such as host-plant rela- ards & Davies 1977, Moritz 1997). This terminology tionships, faunistics or pests in international trade, it is used throughout the literature on Thysanoptera. is common that only larvae are available, and iden- The larvae have been described for some common tification of these is hampered by the lack of keys to or pest species of Terebrantia, but there are almost immatures. In particular, immatures of the large sub- no descriptions of the pupae. Larvae and pupae are order Terebrantia are often collected, but can only be easily overlooked because they are so small, but the identified with molecular identification techniques pupae are even less often encountered because they or after rearing to the adult stage. occur typically in the soil or hidden within recesses The Thysanoptera have two active immature stages, on plants. Most studies of immature thrips stages known as larva I and larva II, and two or three have focused on the second instar larvae, since these Tijdschrift voor Entomologie 153: 99–160, Figs 1–285. [ISSN 0040–7496]. http://www.nev.nl/tve © 2010 Nederlandse Entomologische Vereniging. Published 1 June 2010. Downloaded from Brill.com10/07/2021 11:28:11PM * Corresponding author via free access 100 Tijdschrift voor Entomologie, volume 153, 2010 Table 1. Identification keys for second instar larvae of Thripidae Subject reference number of species Europe Priesner 1928 58 Principally injurious glasshouse thrips Speyer & Parr 1941 27 Europe Priesner 1964 89 Sericothrips in Illinois Vance 1974 11 Kurtomathrips in Mexico Gerdes, 1980 2 Cultivated plants in Japan Miyazaki & Kudo 1986 12 Common in flowers in Australia Kirk 1987 5 Morus bombycis in Japan Miyazaki & Kudo 1989 4 Common British species Kirk 1996 15 Granite belt stonefruit trees in Australia Milne et al. 1997 5 Frankliniella in Europe Nakahara & Vierbergen 1999 7 Hydatothrips in Japan Kudo 1998 7 Frankliniella spp. and Thrips tabaci in Argentina Borbon 2007 6 are easiest to find and study, but identification keys are usually not available for them and as a result rel- evant data are lost. This paper will help to provide a better understanding of thrips larvae. Material and methods Identification keys for second instar larvae H. Priesner (1891–1974) was the first to provide descriptions of larvae of many European species and to publish keys “for their convenient separation” (Speyer & Parr 1941, Zur Strassen 1975). He stud- ied the second larval instar not only of the Thripi- dae, but also of the large families Aeolothripidae and Phlaeothripidae which were keyed out by him (Pries- ner 1928, 1964). However, there are problems when identifying most species with Priesner’s keys, because they are characterized by only one or a few charac- ters, without figures. Additionally, some of the larvae studied by Priesner to create a dichotomous key did not belong to the species he assigned them to. Later on, several authors have given detailed descriptions of Thripidae larvae, partly or completely derived from rearing experiments (Table 1). These studies usually treat a restricted group of species, either found in a specific habitat or a taxonomic selection. At the VIIth International Symposium on Thysanoptera and Tospoviruses at Reggio Calabria, Italy, Septem- ber 2000, S. Nakahara presented a comprehensive key to 117 species and 27 genera mostly encoun- tered during inspection of agricultural consignments imported into the USA. This key, together with the Thripidae key of Priesner (1964), is used as the basis 1 2 for the key presented here. The nomenclature we Figs 1–2. Second instar larvae. – 1, Frankliniella occi- use is according to Zur Strassen (2003) and Mound dentalis, on leaf tissue; 2, Thrips angusticeps, macerated, (2008). on a microscope slide. Downloaded from Brill.com10/07/2021 11:28:11PM via free access Vierbergen et al.: Key to second instar Thripidae 101 D3 D2 D1 D4 D3 D2 D4 D5 VII Sc D6 D1 D7 3 VI V Sp D3 D1 D2 IV 4 Cs D1 D2 Cs III D1 D2 5 6 Figs 3–6. Chaetotaxy and indication of spiracles, pores and sense cones, reference microscopy. – 3-4, Thrips vulga- tissimus, Chaetotaxy of head and pronotum (3) chaetotaxy of abdominal tergite II, Sp – spiracle (4); 5, Pezothrips dianthi, chaetotaxy of abdominal tergites IX and X, Cs – campaniform sensilla; 6, T. major, right antennal segments III-VII, Sc – sense cone. Fourteen North American species were keyed out of entry, Nakahara & Vierbergen (1999) published for the second instar larvae by Vance (1974). Miya- a key to the larvae II of the European Frankliniella zaki & Kudo (1986) gave excellent descriptions of Karny, 1910 species. Kirk (1987) keyed out both lar- the larvae II of twelve Japanese thrips pest species val instars of five Australian flower thrips species. In in a study forming part of a research programme to addition Milne et al. (1997) provided a key to both develop control measures for the recently introduced larval instars of five species occurring on stonefruit Thrips palmi Karny, 1925. To identify species harm- in Queensland, including the recently introduced ful to crops, and, additionally, to make decisions Frankliniella occidentalis (Pergande, 1895). about infested agricultural shipments at the port Downloaded from Brill.com10/07/2021 11:28:11PM via free access 102 Tijdschrift voor Entomologie, volume 153, 2010 V1 V3 V1 V2 V3 7 8 Figs 7–8. Thrips palmi Karny, abdominal sternite IX. – 7, female larva II; 8, male larva II. Sampling and preparation of body shape is difficult to perform. Often larvae The unwinged thrips larvae (Fig. 1) can be collected are insufficiently macerated or the body is flattened by the methods 1–6 described by Mantel & Vierber- by the weight of the coverslip, resulting in e.g. invis- gen (1996). Depending on the objective for studying ibility of abdominal tergites and sternites through larvae some methods are much more efficient than lack of body content. Preservation in AGA is prob- others. Dr. I. Zawirska (Institute of Plant Protection, ably best to prevent such anomalies (Gutierrez 1985, Poznan, Poland) and the second author collected Rondon 2009). plant material in linen bags, which was subsequently After mounting in a hydrophilic medium the cov- analyzed at the laboratory. The plant material was erslip should be ringed with an additional medium dissected carefully under the stereomicroscope with such as Glyptal (used in acarology: Faraji & Bakker, the aim of detecting thrips specimens that were hid- 2008). Without a surrounding medium, air will pen- den in plant tissue, including larvae. This sampling etrate under the coverslip and subsequently destroy method is time consuming, but damage symptoms the larval specimen over time. and larval host plant relationships can be established better. Morphology and nomenclature Preparation for microscopic study of Thripidae lar- Speyer & Parr (1941) and Heming (1991) described vae (Fig. 2) is completely different from prepara- the morphological features of some Terebrantia sec- tion of the well chitinized adult thrips and larvae of ond instar larvae in detail and the chaetotaxal ter- some large Phlaeothripidae (Kobro & Rafoss 2001). minology they proposed is followed here with some Non-permanent slides of adults or larvae can be pre- minor changes. We use the same numbers and char- pared in a droplet of lactic acid under a coverslip and acters for setae, but these are preceded by a ‘D’ or heated (70° C) for 10–15 minutes. For permanent a ‘V’ respectively according to whether they are on slides, adults can be mounted in Canada balsam, a dorsal or ventral body segment (Figs 3–5).