Gymnetron tibiellum Desbrochers des Loges, 1900

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

publication ID	https://dx.doi.org/10.3897/zookeys.1090.78741
publication LSID	lsid:zoobank.org:pub:DA810EFD-D63C-49C4-B1CA-D346B3C00C37
persistent identifier	https://treatment.plazi.org/id/3BD385E8-BAA4-502A-AEAD-CC91E2490919
treatment provided by	ZooKeys by Pensoft
scientific name	Gymnetron tibiellum Desbrochers des Loges, 1900
status

Treatment

Material examined.

Serbia, Bela Palanka, 43°13.150'N, 22°18.886'E, 288 m, ex Veronica anagallis-aquatica , 29.06.2020, leg. Toševski (9 larvae and 9 pupae) GoogleMaps .

Description of mature larva

(Figs 1A, B View Figure 1 , 2A-F View Figure 2 , 3A-C View Figure 3 ). 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 View Figure 1 ).

Colouration. Head pale brown (Fig. 1B View Figure 1 ). All thoracic and abdominal segments white, cuticle smooth (Fig. 1A View Figure 1 ).

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

Head capsule (Figs 1B View Figure 1 , 2A View Figure 2 ). 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 View Figure 2 ). Fs1 absent; fs2 short, located medially; fs3 short; fs4 short, located anteriorly; and fs5 long, located anterolaterally, close to antenna (Fig. 2A View Figure 2 ). Les1 and les2 as long as des5; one short ves. Epicranial area with six postepicranial setae.

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 View Figure 2 ).

Clypeus (Fig. 2C View Figure 2 ) ~ 3 × as wide as long with two medium cls, located posterolaterally, without sensillum; fused to labrum.

Mouth parts. Labrum (Fig. 2C View Figure 2 ) ~ 2 × 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 View Figure 2 ) 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 View Figure 2 ) with two relatively long, piliform mds, located in distinct holes. Maxilla (Fig. 2F View Figure 2 ): 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 View Figure 2 ) oval, with one long prms; ligula with sinuate margin and two short ligs; premental sclerite broad, well visible. Postlabium (Fig. 2F View Figure 2 ) 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 View Figure 3 ) 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 View Figure 3 ) 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 View Figure 3 ) almost identical to that of mesothorax. Each pedal area of thoracic segments well separated, with three long and two short pda.

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 View Figure 3 ) 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 View Figure 3 ) 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 View Figure 3 ) with two short ds; two short ps; and two very short sts. Abdominal segment X (Fig. 3C View Figure 3 ) with two minute setae (ts).

Description of pupa

(Figs 4A-C View Figure 4 , 5A-C View Figure 5 ). Measurements (in mm). Body length: 1.87-2.50. Body width: 0.62-1.25. Thorax width: 0.67-1.12.

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 × 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 View Figure 5 ).

Chaetotaxy. Sparse, setae short to medium, transparent. Head with one medium os. Rostrum without setae (Fig. 5B View Figure 5 ). 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 View Figure 5 ). 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 View Figure 5 ).

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.