Description of immature stages of Gymnetron species (Coleoptera, Curculionidae, Curculioninae), with particular emphasis on the diagnostic morphological characters at the generic and specific levels Author Skuhrovec, Jiri https://orcid.org/0000-0002-7691-5990 Group Function of Invertebrate and Plant Biodiversity in Agro-Ecosystems, Crop Research Institute, Prague 6 - Ruzyne, Czech Republic jirislavskuhrovec@gmail.com Author Gosik, Rafal Department of Zoology and Nature Protection, Institute of Biological Sciences, Maria Curie-Sklodowska University, Akademicka 19, 20 - 033 Lublin, Poland Author Caldara, Roberto Center of Alpine Entomology, University of Milan, Via Celoria 2, 20133 Milan, Italy Author Tosevski, Ivo CABI, Rue des Grillons 1, 2800 Delemont, Switzerland & Institute for Plant Protection and Environment, Banatska 33, 11080 Zemun, Serbia Author Batyra, Aleksandra Zabia Wola 75 H, 23 - 107 Strzyzewice, Poland text ZooKeys 2022 2022-03-23 1090 45 84 http://dx.doi.org/10.3897/zookeys.1090.78741 journal article http://dx.doi.org/10.3897/zookeys.1090.78741 1313-2970-1090-45 DA810EFDD63C49C4B1CAD346B3C00C37 2FE2177128BF5B8092D3A251DBEA4129 Gymnetron tibiellum Desbrochers des Loges, 1900 Material examined. Serbia , Bela Palanka , 43°13.150'N , 22°18.886'E , 288 m , ex Veronica anagallis-aquatica , 29.06.2020 , leg. Tosevski ( 9 larvae and 9 pupae ) . Description of mature larva (Figs 1A, B , 2A-F , 3A-C ). Measurements (in mm). Body length: 2.25-2.50. The widest point in the body (meso- and metathorax) measures up to 0.95. Head width: 0.42-0.45. General . Body elongate, slender, weakly curved, rounded in cross section (Fig. 1A ). Figure 1. Gymnetron tibiellum Desbrochers des Loges mature larva A habitus B head, dorsal view. Scale bars: 0.5 mm ( A ); 0.25 mm ( B ). Colouration . Head pale brown (Fig. 1B ). All thoracic and abdominal segments white, cuticle smooth (Fig. 1A ). Vestiture . Setae on body thin, yellowish, distinctly different in length (minute to very short or long). Head capsule (Figs 1B , 2A ). Head suboval, endocarinal line present, extending for 2/3 of length of frons. Frontal sutures on head very broad and distinct. Stemma, in the form of a very small pigmented spot with convex cornea. Des1 long, located in middle of central part of epicranium; des2 medium; des3 long, located anteriorly on epicranium close to border with frontal suture; des4 short; des5 long, located anterolaterally above stemma (Fig. 2A ). Fs1 absent; fs2 short, located medially; fs3 short; fs4 short, located anteriorly; and fs5 long, located anterolaterally, close to antenna (Fig. 2A ). Les1 and les2 as long as des5 ; one short ves . Epicranial area with six postepicranial setae. Figure 2. Gymnetron tibiellum Desbrochers des Loges mature larva, head and mouth parts A head B antenna C clypeus and labrum D epipharynx E left mandible F maxillolabial complex. Abbreviations: at - antenna, lr - labral rods, sa - sensillum ampullaceum, sb - sensillum basiconicum, Se - sensorium, st - stemma; setae: als - anteriolateral, ams - anteromedial, cls - clypeal, des - dorsal epicranial, dms - dorsal malar, fs - frontal epicranial, les - lateral epicranial, ligs - ligular, lms - labral, mbs - basioventral, mds - mandibular dorsal, mpxs - maxillary palps, pes - postepicranial, pfs - palpiferal, pms - postmental, prms - premental, stps - stipital, ves - ventral, vms - ventral malar. Antennae membranous and distinctly convex basal membranous article bearing one relatively long conical sensorium and three sensilla of different types: two basiconical and one ampullaceum (Fig. 2B ). Clypeus (Fig. 2C ) ~ 3 x as wide as long with two medium cls , located posterolaterally, without sensillum; fused to labrum. Mouth parts . Labrum (Fig. 2C ) ~ 2 x as wide as long, with three piliform lms , relatively long, of almost equal length; lms1 located anteromedially, lms2 located partly close to clypeus, and lms3 located anterolaterally. Epipharynx (Fig. 2D ) with three very long digitate als , almost identical in length; with two piliform, medium ams ; without mes ; labral rods indistinct, irregular in shape. Mandibles (Fig. 2E ) with two relatively long, piliform mds , located in distinct holes. Maxilla (Fig. 2F ): stipes with one stps , two pfs and with one mbs and one sensillum, stps and both pfs1-2 relatively long; mala with four elongate, digitate dms ; four vms , almost equal in length. Maxillary palpi with two palpomeres; length ratio of basal and distal palpomeres: 1:0.6. Praelabium (Fig. 2F ) oval, with one long prms ; ligula with sinuate margin and two short ligs ; premental sclerite broad, well visible. Postlabium (Fig. 2F ) with three pms , medium pms1 located medially, elongated pms2 located laterally, and medium pms3 located anterolaterally; membranous area sparsely and finely asperate. Thorax . Prothorax (Fig. 3A ) with 11 long and one short to minute prns , small pigmented dorsal sclerite present with five long and one short prns , this sclerite subdivided into two triangular plates medially; two long ps ; and two short to very short eus . Mesothorax (Fig. 3A ) without prs , two long and one short pds ; one long as ; two long and one very short to minute ss ; one long eps ; one long ps ; and two short eus . Chaetotaxy of metathorax (Fig. 3A ) almost identical to that of mesothorax. Each pedal area of thoracic segments well separated, with three long and two short pda . Figure 3. Gymnetron tibiellum Desbrochers des Loges mature larva, habitus A lateral view of thoracic segments B lateral view of abdominal segment I C lateral view of abdominal segments VI-X. Abbreviations: Th1-3 - numbers of thoracic segments, Ab1-10 - numbers of abdominal segments, setae: as - alar, ds - dorsal, eps - epipleural, eus - eusternal, lsts - laterosternal, pda - pedal, pds - postdorsal, prns - pronotal, prs - prodorsal, ss - spiracular, ps - pleural, sts - sternal, ts - terminal. Abdomen . Spiracles on abdominal segments I-VI close to anterior margin, functional, spiracles on abdominal segment VII not functional. Abdominal segments I-VII (Fig. 3B, C ) with two minute prs ; two long pds ; one long and one very short to minute ss ; one short eps ; one short ps ; one short lsts ; and two very short and sometimes one additional minute eus . Abdominal segment VIII (Fig. 3C ) with two minute prs ; two long pds ; one very short to minute ss ; one short eps ; one short ps ; one short lsts ; and two very short and sometimes one additional minute eus . Abdominal segment IX (Fig. 3C ) with two short ds ; two short ps ; and two very short sts . Abdominal segment X (Fig. 3C ) with two minute setae ( ts ). Description of pupa (Figs 4A-C , 5A-C ). Measurements (in mm). Body length: 1.87-2.50. Body width: 0.62-1.25. Thorax width: 0.67-1.12. Figure 4. Gymnetron tibiellum Desbrochers des Loges pupa habitus A ventral view B lateral view C dorsal view. Scale bars: 0.5 mm. Body . Brownish, pronotal protuberances (p-pr) sclerotized, covered with conical asperities; apical parts of femora, head, rostrum and pronotum darker than rest of body. Rostrum moderately slender. Pronotal protuberances fused at base. Pronotum 1.5 x as wide as long. Mesonotum slightly smaller than metanotum. Urogomphi in form of minute sclerotized protuberances, almost invisible. Abdominal segment VIII dorsally with rounded, prominent abdominal protuberance (a-pr) (Fig. 5A-C ). Chaetotaxy . Sparse, setae short to medium, transparent. Head with one medium os . Rostrum without setae (Fig. 5B ). Pronotum with one as , one ds , two sls , one ls and three pls almost equal in length. Dorsal parts of meso- and metathorax with two setae of various length, placed medially. Apex of pro- and mesofemora with two medium-sized fes , metafemora with one seta (Fig. 5A-C ). Abdominal segments I-VIII with three short setae of equal length dorsally: first placed medially, the next two more laterally. Each lateral part of abdominal segments I-VIII with single, medium-sized seta. Ventral parts of abdominal segments I-VIII with three medium-sized setae. Abdominal segment IX with two minute setae ventrally (Fig. 5A-C ). Figure 5. Gymnetron tibiellum Desbrochers des Loges pupa habitus A ventral view B dorsal view C lateral view. Abbreviations: a-pr - abdominal protuberances, p-pr - pronotal protuberances, ur - urogomphi; setae: as - apical, d - dorsal, ds - discal, fes - femoral, l , ls - lateral, os - orbital, pls - posterolateral, sls - superlateral, v - ventral. Biological notes. The immature stages of G. tibiellum were collected from capsules of Veronica anagallis-aquatica L. Previously, nothing was known about the biology of this species. The adults are active from mid-April following the appearance of the host plants. Oviposition takes place from early June until mid-August. The presence of larvae inside the seed capsules is readily detected from the dark colour of the deposited frass. The biologies of G. tibiellum and G. veronicae are very similar but no competition between these two weevil species has been observed in over 500 dissected seeds capsules where they occur in syntopy. Remarks and comparative notes. Gymnetron tibiellum is widely distributed in the south-eastern part of central Europe, Italy, the Balkans, Caucasus, Anatolia and the Middle East ( Alonso-Zarazaga et al. 2017 ). The adults of this species are very closely related to G. veronicae , from which they differ by the shape of the rostra and the penis ( Caldara 2008a ). This close relationship was confirmed here by several characters which the immature stages have in common, although differences in several other characters of both larvae and pupae readily discriminate these two species.