Gymnetron veronicae (Germar, 1821)

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 veronicae (Germar, 1821)

Material examined.

Serbia, Gornji Milanovac, Donja Vrbava , GPS 44°1.663'N, 20°34.496'E, 370 m, ex Veronica anagallis-aquatica , 20.06.2020, leg. Toševski (4 larvae and 4 pupae) .

Description of mature larva

(Figs 6A, B , 7A-F , 8A-C ). Measurements (in mm). Body length: 2.16-3.00. The widest point in the body (meso- and metathorax) measures up to 1.00. Head width: 0.50-0.53.

General. Body elongate, slender, weakly curved, rounded in cross section (Fig. 6A ).

Colouration. Head dark brown (Fig. 6B ). All thoracic and abdominal segments white with numerous reddish or brown asperities (Fig. 6A ).

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

Head capsule (Figs 6B , 7A ). Head suboval, flattened laterally, endocarinal line present, clearly extending to half the 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 the central part of epicranium; des2 short, placed medially; des3 relatively long, located anteriorly on epicranium close to border with frontal suture; des4 short, placed above frontal suture; des5 long, located anterolaterally (Fig. 7A ). Fs1 short; fs2 absent; fs3 located medially; fs4 short, located anteriorly; and fs5 long, located anterolaterally, close to antenna (Fig. 7A ). Les1 and les2 as long as des5; one ves minute. Epicranial area with four postepicranial setae.

Antennae membranous and distinctly convex basal membranous article bearing one relatively long conical sensorium and six sensilla different in length (four basiconica and two ampullacea) (Fig. 7B ).

Clypeus (Fig. 7C ) ~ 3 × as wide as long with two medium cls, located posterolaterally, without sensillum; fused to labrum.

Mouth parts. Labrum (Fig. 7C ) ~ 4 × as wide as long, three piliform lms, relatively long but of different lengths; lms1 located anteromedially, lms2 located partly close to clypeus, and lms3 located anterolaterally, lms1 and lms2 relatively elongate, lms3 short. Epipharynx (Fig. 7D ) with two very long digitate als, almost identical in length; with three ams of different length, ams1 and ams2 piliform and short, ams3 digitate and enlarged in middle; without mes; labral rods indistinct, irregular in shape. Mandibles (Fig. 7E ) with two relatively long, piliform mds, located in distinct holes. Maxilla (Fig. 7F ): stipes with one stps, two pfs and one minute mbs and one sensillum, stps and both pfs relatively long; mala with five medium, digitate dms; four vms, of different lengths, two setae very short, and two setae minute. Maxillary palpi with two palpomeres; length ratio of basal and distal palpomeres: 1:0.5. Praelabium (Fig. 7F ) suboval-shaped, with one medium prms; ligula with sinuate margin and two very short ligs; premental sclerite broad, well visible. Postlabium (Fig. 7F ) with three pms: pms1 very long; pms2 short, located medially; pms3 located laterally; membranous area densely and finely asperate.

Thorax. Prothorax (Fig. 8A ) with seven long and one short prns, small pigmented dorsal sclerite present with three long prns, this sclerite subdivided into two triangular plates medially; two long ps; and two short to very short eus. Mesothorax (Fig. 8A ) with two very short to minute prs; one short and two long pds; one long as; one long and two very short to minute ss; one long eps; one long ps; and two short eus. Chaetotaxy of metathorax (Fig. 8A ) almost identical to that of mesothorax. Each pedal area of thoracic segments well separated, with three long and two very short to minute 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-VII (Fig. 8B, C ) with two minute prs (segment VII with one prs); one long and one minute pds; one long and one very short to minute ss; one long eps; one relatively long ps; one short lsts; and two very short and sometimes one additional minute eus. Abdominal segment VIII (Fig. 8C ) with one minute prs; one long pds; one very short to minute ss; one long eps; one relatively long ps; one short lsts; and two very short and sometimes one additional minute eus. Abdominal segment IX (Fig. 8C ) with one relatively long ds; one relatively long ps; and one short to very short sts. Abdominal segment X (Fig. 8C ) with one very short seta (ts).

Description of pupa

(Figs 9A-C , 10A-C ). Measurements (in mm). Body length: 2.12-2.32. Body width: 1.25-1.23, Thorax width: 0.70-0.80.

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 almost completely fused. Pronotum twice as wide as long. Mesonotum slightly smaller than metanotum. Urogomphi short, conical, with sclerotized apices. Abdominal segment VIII with rounded, prominent abdominal protuberance dorsally (a-pr) (Fig. 10A-C ).

Chaetotaxy. Sparse, setae short to medium, transparent. Head with one medium os. Rostrum without setae (Fig. 10B ). Pronotum with two elongate as, one ds, one sls, and three pls, all of almost equal length. Dorsal parts of meso- and metathorax with three setae of various length, situated medially. Apex of femora with two medium-sized fes (Fig. 10A-C ). Abdominal segments I-VIII with four medium to short setae placed in horizontal line medially. Each lateral part of abdominal segments I-VIII with two setae of various size. Ventral parts of abdominal segments I-VIII with three medium setae. Abdominal segment IX with two minute setae ventrally (Fig. 10A-C ).

Biological notes.

The larva was already known to feed on the ovary of Veronica beccabunga L, where it pupates and develops to the adult stage, and the adult was also collected on V. anagallis-aquatica L. and V. scutellata L. ( Hoffmann 1958; Koch 1992; Sprick 1997). We can now confirm that at least V. anagallis-aquatica L. must be another host plant. The biology of this weevil species is the same as that of G. tibiellum .

Remarks and comparative notes.

The adult of this species, widely distributed throughout Europe ( Alonso-Zarazaga et al. 2017), is closely related to G. tibiellum , but with which it is sympatric only in south-eastern Europe. The two species differ mainly in the shapes of the rostra and the penis. Examination of the larvae confirms the relationship between them: they share the praedorsal segment on the abdominal segments with two pds, the epicranium with fs3 and the labral setae in one line. However, the larva of G. veronicae differs from that of G. tibiellum by the cuticle of the body covered with numerous reddish or brown asperities and setae emerging from black spots, the dark brown not pale yellow head, and the epipharynx with two (not three) als and three (not two) ams. The pupae also have many characters in common (see the key), but clearly differ by the number of setae as, ls and sls on the pronotum, those on the meso- and metathorax, and on the dorsal parts of abdominal segments I-VII.

Figures

Figure 6. Gymnetron veronicae (Germar) mature larva A habitus B head, dorsal view. Scale bars: 0.5 mm (A); 0.25 mm (B).

Figure 7. Gymnetron veronicae (Germar) 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.

Figure 8. Gymnetron veronicae (Germar) 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 9. Gymnetron veronicae (Germar) pupa habitus A ventral view B lateral view C dorsal view. Scale bars: 0.5 mm.

Figure 10. Gymnetron veronicae (Germar) 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 - lateral, os - orbital, pls - posterolateral, sls - superlateral, v - ventral.