Rhinusa pilosa (Gyllenhal, 1838)

Gosik, Rafal, Caldara, Roberto, Tosevski, Ivo & Skuhrovec, Jiri, 2024, Description of immature stages of Rhinusa species (Coleoptera, Curculionidae, Mecinini) with a focus on diagnostic morphological characters at the species and genus levels, ZooKeys 1195, pp. 1-94 : 1

6) Rhinusa pilosa (Gyllenhal, 1838)

Material examined.

4 mature larvae; 3 ♂ and 5 ♀ pupae. Serbia, Zemun , ex Linaria vulgaris galls, 01.06.2018, leg., det. I. Toševski.

Description of mature larva

(Figs 26A, B , 27A-E , 28A-C ). Measurements (in mm). Body length: 4.00-5.75 (avg. 4.25). The widest place in the body (meso- and metathorax) measures up to 1.50. Head width: 0.60-0.68 (avg. 0.65).

General. Body elongate, slightly curved, rounded in cross section (Fig. 26A ). Prothorax slightly smaller than mesothorax, pronotal shield not pigmented. Meso- and metathorax equal in size; each divided dorsally into two folds (prodorsal fold distinctly smaller than postdorsal fold); postdorsal fold of metathorax conical. Pedal folds of thoracic segments isolated, prominent. Abdominal segments I-VI of similar size, next segments tapering towards posterior body end. Abdominal segments I-VII each divided dorsally into two folds of almost identical size; postdorsal folds of segments I-VI higher than prodorsal folds. Segments VIII and IX dorsally undivided. Epipleural folds of segments I-VIII conical. Laterosternal and eusternal folds of segments I-VIII weakly isolated. Abdominal segment X divided into four folds of equal size. Anus situated ventrally, almost completely covered with the ninth abdominal segment.

All spiracles unicameral; thoracic spiracles (Fig. 26A ) placed laterally close to mesothorax; abdominal spiracles (Fig. 26A ) placed anteromedially on segments I-VIII.

Colouration. Light yellow to dark yellow head, medial parts of epicranium less sclerotised (Fig. 26B ). All thoracic and abdominal segments whitish (Fig. 26A ). Cuticle covered with asperities.

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

Head capsule (Figs 26B , 27A ). Head wide, endocarinal line present, reaching to 2/3 length of frons. Frontal sutures on head indistinct, very wide. Single pair of stemmata in the form of small black spots (st) close to the end of the frontal suture. Des1 short, located in middle part of epicranium; medium des2; long des3 located anteriorly on epicranium close to the border with the frontal suture; des4 minute; and des5 long, located anterolaterally above stemma (Fig. 27A ). Fs1 and fs2 absent; fs3 minute; fs4 medium, located anteriorly; and long fs5 located anterolaterally, close to antenna (Fig. 27A ). Les1 and les2 medium; single short ves. Epicranial area with a single pes.

Antennae placed distally of the frontal suture, on the inside; membranous and distinctly convex basal article bearing one conical relatively short sensorium, plus three sensilla basiconica (Fig. 27B ).

Clypeus and labrum (Fig. 27C ) completely fused, trapezoidal, 3 × as wide as long, with two short cls, localised posteriorly three medium piliform lrs, located anteromedially. Epipharynx (Fig. 27C ) with two finger-like elongated als; and two piliform ams, variable in length; labral rods (lr) indistinct, close to oval-shape; anterior border almost straight.

Mouth parts. Mandibles (Fig. 27D ) bifid, cutting edge with blunt additional teeth; two short piliform mds, close to lateral border. Maxillolabial complex: maxilla more sclerotised than labium (Fig. 27E ) stipes with one stps, two pfs and one very short mbs and one sensillum, stps and both pfs1-2 relatively short; mala with four finger-like dms variable in length; four piliform vms, medium to short in length. Maxillary palpi two-segmented; basal palpomere distinctly wider than distal one; length ratio of basal and distal palpomeres almost 1:2; basal palpomere with short mpxs and two sensilla, distal palpomere with a group of five apical sensilla in terminal receptive area. Prementum (Fig. 27E ) oval-shaped, with one short prms; ligula with round margin and two minute ligs; premental sclerite vestigial, only lateral parts highly sclerotised, posterior extension absent. Labial palpi one-segmented; palpi very small, with a single pore, and a group of three or four apical sensilla (ampullacea) on terminal receptive area; surface of labium smooth. Postmentum (Fig. 27E ) with three pms, short pms1 located posteromedially, medium pms2 located mediolaterally, and short pms3 located anterolaterally; membranous area smooth.

Thorax. Prothorax (Fig. 28A ) with seven elongated to medium prns; two medium ps; and single short eus. Mesothorax (Fig. 28A ) without prs; with two medium pds; one medium as; three ss (two medium and one short); one medium eps; one medium ps; and single minute eus. Chaetotaxy of metathorax (Fig. 28A ) almost identical to that of mesothorax. Each pedal area of thoracic segments with five pda of various length.

Abdomen. Segments I-VIII (Fig. 28B, C ) without prs; with two medium pds; one minute and one medium ss; one medium eps; one medium ps; one short lsts; and two minute eus. Abdominal segment IX (Fig. 28C ) with two minute ds; one minute ps; and two minute sts.

Description of pupa

(Figs 29A-C , 30A-C ). Measurements (in mm). Body length: 2.86-3.75 (avg. 3.25); body width: 1.90-2.25 (avg. 2.00); thorax width: 1.10-1.35 (avg. 1.25); rostrum length: up to 0.40 ♂, ♀.

Body. Integument white, with some parts dark sclerotised; moderately elongated, curved. Head protuberances (h-pr) elongated. Rostrum rather stout, on both sexes almost 2.3 × as long as wide, extended only to procoxae. Pronotum trapezoidal 3 × as wide as long. Pronotal protuberances (p-pr) absent. Meso- and metanotum similar in size. Abdominal segments I-VI almost identical in size; segment VII semicircular; segment VIII narrow; segment IX reduced. Abdominal protuberances (a-pr) absent. Urogomphi (ur) medium-sized, ending with sclerotised, sharp apexes (Fig. 29A-C ).

Chaetotaxy. Well developed, setae minute to elongated. Minute and medium setae transparent, elongated setae basally brown, apically transparent. Head with one minute os (Fig. 30A ). Rostrum with a single minute pas. Pronotum with three as, single ls, and two pls; all pronotal setae almost equally in length, prominent, basally brownish, apically transparent. Dorsal parts of meso- and metathorax with two identical in length setae, placed medially. Setae of mesothorax as long as those on pronotum. Apex of femora with a single long fes (Fig. 30A-C ). Abdominal segments I-VI with three setae: first and second minute placed anteromedially, third medium placed below stigma. Abdominal segments VII with three elongated setae dorsally and segment VIII with two elongated setae dorsally. Each lateral part of abdominal segments I-VII with a single medium seta. Ventral parts of abdominal segments I-VIII with two minute setae. Abdominal segment IX with two minute setae ventrally (Fig. 30A-C ).

Remarks and comparative notes.

This species is distributed in northern and central Europe and in the Balkans ( Alonso-Zarazaga et al. 2023). It is distinguishable from other species of the R. pilosa group by the rostrum being markedly bent at the level of antennal insertion in both sexes. It is a unique species in the group in being distributed northwards in the western Palaearctic, associated only with L. vulgaris as a host plant. All three species of this group differ from the other species of Rhinusa by the very long, hair-like scales of the dorsal vestiture.

Biological notes.

Rhinusa pilosa is a shoot-galling weevil associated with L. vulgaris for larval development. Adults become active in early spring, and their appearance after winter hibernation coincides with the intensive shoot growth of their host plant. Females oviposit in the upper part of the young, growing shoots of L. vulgaris . Females oviposit three to six eggs, but the number of ovipositions has been observed to exceed 17 per shoot. Oviposition provokes the induction of a globose or elyptical gall on the apical part of the stem. Larvae feed and complete development within the induced galls. Pupation is also completed within the gall. Eclosed adults intensively feed on gall tissue, after which they leave the gall and enter into summer aestivation within the soil litter or soil cracks. In late autumn, adults are briefly active, feeding on young L. vulgaris shoots before entering diapause, sheltering close to the host plant. The biology of R. pilosa is described in detail by Gassmann et al. (2014).

Figures

Figure 26. Rhinusa pilosa (Gyllenhal, 1838) mature larva A habitus B head, frontal view.

Figure 27. Rhinusa pilosa (Gyllenhal, 1838) mature larva, head and mouth parts A head B antenna C clypeus and labrum (left side), epipharynx (right side) D left mandible E maxillolabial complex (schemes). Abbreviations: at-antenna, lr-labral rods, sb-sensillum basiconicum, Se-sensorium, st-stemmata, setae: als - anterolateral, ams - anteromedial, cls - clypeal, des - dorsal epicranial, dms - dorsal malar, fs - frontal epicranial, les - lateral epicranial, ligs - ligular, lrs - labral, mbs - malar basiventral, mds - mandibular dorsal, mpxs - maxillary palp, pes - postepicranial, pfs - palpiferal, pms - postmental, prms - premental, stps - stipital, ves - ventral, vms - ventral malar.

Figure 28. Rhinusa pilosa (Gyllenhal, 1838) mature larva, habitus A lateral view of thoracic segments B lateral view of abdominal segment I C lateral view of abdominal segments VII-X (schemes). Abbreviations: Th. 1 - 3 - number of thoracic segments, Abd. 1 - 10 - number of abdominal seg, setae: as - alar, ds - dorsal, eps - epipleural, eus - eusternal, lsts - laterosternal, pda - pedal, pds - postdorsal, prns - pronotal, ss - spiracular, ps - pleural, sts - sternal.

Figure 29. Rhinusa pilosa (Gyllenhal, 1838) pupa habitus A ventral view B lateral view C dorsal view.

Figure 30. Rhinusa pilosa (Gyllenhal, 1838) pupa habitus A ventral view B dorsal view C lateral view (schemes). Abbreviations: h-pr-head protuberances, ur-urogomphi, setae: as - apical, d - dorsal, fes - femoral, l, ls - lateral, os - orbital, pas - postantennal, pls - posterolateral, v - ventral.