Gymnetron rotundicolle Gyllenhal, 1838

Skuhrovec, Jiri, Gosik, Rafal, Caldara, Roberto, Tosevski, Ivo & Batyra, Aleksandra, 2022, Description of immature stages of Gymnetron species (Coleoptera, Curculionidae, Curculioninae), with particular emphasis on the diagnostic morphological characters at the generic and specific levels, ZooKeys 1090, pp. 45-84 : 45

Gymnetron rotundicolle Gyllenhal, 1838

Material examined.

Serbia, Kalna , GPS 43°24.673'N, 22°25.737'E, 365 m, ex Veronica hederophylla , 20.06.2020, leg. Toševski (20 larvae) ; Serbia, Zemun , GPS 44°51.313'N, 20°22.625'E, 105 m, ex V. opaca , 19.06.2020, leg. Toševski (4 larvae and 2 pupae) .

Description of mature larva

(Figs 11A, B , 12A-F , 13A, B ). Measurements (in mm). Body length: 2.20-2.33. The widest point in the body (meso- and metathorax) measures up to 0.86. Head width: 0.36-0.50.

General. Body relatively elongate, distinctly curved, rounded in cross section (Fig. 11A ).

Colouration. Head pale yellow (Fig. 11B ). All thoracic and abdominal segments white, cuticle smooth (Fig. 11A ).

Vestiture. Setae on body thin, transparent, distinctly different in length (minute to very short or medium).

Head capsule (Figs 11B , 12A ). Head suboval, endocarinal line present, shorter than half the length of frons. Frontal sutures on head of medium width, distinct. Stemma, in form of distinct, black pigmented spot with convex cornea. Des1 short, located in middle of central part of epicranium; des2 short, located in middle of central part of epicranium; medium size des3 located anteriorly on epicranium close to border with frontal suture; des4 short, located between des2 and des3; des5 of medium size, located anterolaterally (Fig. 12A ). Fs1 absent; fs2 very short to minute, located medially; fs3 absent; fs4 medium, located anteriorly; and fs5 relatively long, located anterolaterally, close to antenna (Fig. 12A ). Les1 and les2 as long as des5; two ves short. Epicranial area with four postepicranial setae (pes).

Antennae membranous and distinctly convex basal membranous article bearing one relatively long conical sensorium and three sensilla basiconica (Fig. 12B ).

Clypeus (Fig. 12C ) ~ 3 × as wide as long with two relatively long cls: cls1 located posterolaterally, cls2 located posteromedially, and one sensillum between setae; not fused with labrum.

Mouth parts. Labrum (Fig. 12C ) ~ 3 × as wide as long, with three piliform lms, relatively long, of almost equal length; lms1 located posteromedially, close to clypeus, lms2 located anteromedially, and lms3 located anterolaterally. Epipharynx (Fig. 12D ) with three very long digitate als, almost identical in length, two piliform ams almost equal in length and one mes; labral rods indistinct, enlarged anteriorly. Mandibles (Fig. 12E ) with two relatively long, piliform mds, located in distinct holes. Maxilla (Fig. 12F ): stipes with one stps, two pfs, one mbs and sensillum, stps and pfs1-2 long, mbs very short; mala with five relatively long, digitate dms; four vms, different in length, one setae very short, and three setae minute. Maxillary palpi with two palpomeres; length ratio of basal and distal palpomeres: 1:0.5. Praelabium (Fig. 12F ) oval, with one relatively long prms; ligula with sinuate margin and two very short ligs and one sensillum; premental sclerite broad, readily visible at sides but almost invisible in middle. Postlabium (Fig. 12F ) with three pms, very long pms2, and very short to short pms1 and pms3, all located laterally; membranous area sparsely and finely asperate.

Thorax. Prothorax (Fig. 13A ) with six relatively long and one short to very short prns, pigmented dorsal sclerite present with four relatively long prns, this sclerite subdivided into two triangular plates medially; two relatively long ps; and one short eus. Mesothorax (Fig. 13A ) with two very short to minute prs, one relatively long and two short to very short pds; one relatively long as; two relatively long ss; one relatively long eps; one relatively long ps; and one short eus. Chaetotaxy of metathorax (Fig. 13A ) almost identical to that of mesothorax. Each pedal area of thoracic segments well separated, with three long pda.

Abdomen. Spiracles on abdominal segments I-VI close to the anterior margin and functional, spiracles on abdominal segment VII not functional, and abdominal segment VIII with atrophied spiracles. Abdominal segments I-VI (Fig. 13B, C ) with one very short to minute prs; one relatively long and one very short pds; one relatively long and one very short to minute ss; one relatively long eps; two very short ps; one very short lsts; and one very short to minute eus. Abdominal segments VII-VIII (Fig. 13C ) without prs; with one relatively long pds; one very short to minute ss; one relatively long eps; two very short ps; one very short lsts; and one very short to minute eus. Abdominal segment IX (Fig. 13C ) with one very short ds; one very short ps; and two very short sts. Abdominal segment X (Fig. 13C ) with one very short to minute seta (ts).

Description of pupa

(Figs 14A-C , 15A-C ). Measurements (in mm). Body length: 2.20-2.37. Body width: 1.12-1.42, Thorax width: 0.70-0.85.

Body. Yellowish, pronotal protuberances (p-pr) weakly sclerotized, with serrated margins; apical parts of femora brownish. Rostrum slender. Pronotum twice as wide as long. Pronotal protuberances fused at basis. Mesonotum slightly smaller than metanotum. Urogomphi reduced, conical, with sclerotized apex. Abdominal segment VIII with rounded, prominent abdominal protuberance dorsally (a-pr) (Fig. 15A-C ).

Chaetotaxy. Sparse, setae short to medium, transparent. Head with one short os. Rostrum without setae (Fig. 14B ). Pronotum with two as, one ds, and three pls equal in length. Dorsal parts of meso- and metathorax with three setae of different length, situated medially. Apex of femora with one medium fes (Fig. 15A-C ). Abdominal segments I-VIII with two short, equally long setae dorsally: one situated medially, the other mediolaterally. All dorsal abdominal setae almost equal in length, short. Each lateral part of abdominal segments I-VIII with two setae of various length (one short, one minute). Ventral parts of abdominal segments I-VIII with three medium setae. Abdominal segment IX with two very short setae ventrally (Fig. 15A-C ).

Biological notes.

The adults of G. rotundicolle were previously recorded as collected on two species of Veronica : V. persica Poiret in Italy and Switzerland ( Caldara 2008b; Germann et al. 2013), and V. chamaedrys L. in the Czech Republic and Slovakia ( Krátký and Trnka 2012; Krátký 2013). The reports of Veronica hederifolia L. and V. opaca Fr. as host plants of this weevil are new data. The adults appear in early spring (mid-March), feeding on the upper leaves of newly growing shoots of the host. Oviposition takes place in the seed capsules, in which the larvae complete their development. The presence of larvae inside seed capsules can be detected from the dark colour of their frass.

Remarks and comparative notes.

The first findings of this originally central Asian species in many countries of central and southern Europe (Italy, Switzerland, France, Germany, Czech Republic, Slovakia, Hungary, Poland) have been reported in many faunistic papers during the last 15 years ( Strejček 2007; Caldara 2008b; Krátký and Trnka 2012; Krátký 2013; Germann et al. 2013; Reibnitz 2013; Podlussány et al. 2017; Wanat and Ruta 2018; Nolte and Haag 2019). These papers indicate with a high degree of certainty that this species only recently colonized areas where a few years ago it was absent, in contrast to its host plants ( Caldara 2008b; Germann et al. 2013).

Figures

Figure 11. Gymnetron rotundicolle Gyllenhal mature larva A habitus B head, dorsal view. Scale bars: 0.5 mm (A); 0.25 mm (B).

Figure 12. Gymnetron rotundicolle Gyllenhal 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, clss - clypeal sensillium, lr - labral rods, 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, mes - median, mpxs - maxillary palps, pes - postepicranial, pfs - palpiferal, pms - postmental, prms - premental, stps - stipital, ves - ventral, vms - ventral malar.

Figure 13. Gymnetron rotundicolle Gyllenhal 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: Th 1 - 3 - numbers of thoracic segments, Ab 1 - 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.

Figure 14. Gymnetron rotundicolle Gyllenhal pupa habitus A ventral view B lateral view C dorsal view. Scale bars: 0.5 mm.

Figure 15. Gymnetron rotundicolle Gyllenhal 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, v - ventral.