Mecinus pyraster (Herbst, 1795)

Gosik, Rafal, Skuhrovec, Jiri, Caldara, Roberto & Tosevski, Ivo, 2020, Immature stages of Palearctic Mecinus species (Coleoptera, Curculionidae, Curculioninae): morphological characters diagnostic at genus and species levels, ZooKeys 939, pp. 87-165 : 87

Mecinus pyraster (Herbst, 1795)

Material examined.

4 L3 larvae and 5 pupae, Serbia, Zemun, 1.07.2017, GPS 44°39.030'N, 21°28.355'E, 162 m., ex l., ex Plantago lanceolata , lgt. I. Toševski. Accession number of sequenced specimen MN992000.

Description of mature larva

(Figures 13A-D , 14A-F ). Measurements (in mm). Body length: 2.00-2.83. Body width (metathorax or abdominal segments I-II): 0.83-1.00. Head width: 0.53-0.56.

Body (Figure 13A-D ) yellowish, slender, curved, densely covered with asperities. Metathorax as large as abdominal segment I. Abdominal segments I-VI of almost equal length, abdominal segments VII-IX decreasing gradually to the terminal body part, segment X reduced to three anal lobes of those lateral are the largest, and dorsal the smallest (sometimes absent). Chaetotaxy weakly developed, setae short or medium. Prothorax (Figure 13B ) with eleven prns (eight medium and three very short); two medium ps and one very short eus. Meso- and metathorax (Figure 13B ) with one very short prs, two very short pds, one very short as, three ss (two medium and one very short), one medium eps, one medium ps and one very short eus. Pedal area with five pda (three medium and two very short). Abdominal segments I-VIII (Figure 13C, D ) with one very short prs, three very short pds arranged along the posterior margin, two very short ss, two eps different in length, one medium ps, one medium lsts and two very short eus. Abdominal segment IX (Figure 13D ) with three ds (one medium and two very short), all located close to the posterior margin, one medium ps and two very short sts. Each lateral anal lobe with two minute setae.

Head capsule (Figures 13A , 14A-F ) dark brown, narrowed bilaterally. Frontal suture visible. Des1-3,5 very long, equal in length; des4 three times shorter than des1. Fs1,4,5 long; fs3 very short. Les1 and les2 equal in length, slightly shorter than des1; ves1-2 short; pes1-2 short (Figure 14A ). Antennae (Figure 14B ) with sensorium (Se) slender, four times as long as wide, and three sensilla basiconica. Clypeus (Figure 14C ) trapezium-shaped, anterior margin distinctly sinuated; both cls relatively long, clss absent. Labrum (Figure 14C ) with slightly sinuate anterior margin; lrs1 long, lrs2 and lrs3 medium. Epipharynx (Figure 14D ) with three medium, finger-shaped als of almost equal length; two rod-like ams different in length; two finger-like mes of medium length; surface smooth; labral rods close to kidney-shaped. Mandibles (Figure 14E ) conical, wide, with small protuberance in the middle of the cutting edge; one capilliform mds, medium, placed mediolaterally. Maxilla (Figure 14F ) with one stps and two pfs equal in length; mbs very short; mala with six finger-like dms of different size (dms1-2 medium, dms3-6 long to very long), five vms different in length. Maxillary palpi: basal palpomere slightly wider than distal, both palpomeres almost equal in length. Prelabium (Figure 14F ) cup-like with one relatively long prms; ligula with two ligs different in length; premental sclerite well visible, cup-shaped. Labial palpi elongated, one-segmented. Postlabium (Figure 14F ) with medium pms1, long pms2, and medium pms3.

Description of pupa

(Figure 15A-C ). Measurements (in mm). Head width: 0.53-0.63. Body width: 1.40-1.73. Body length: 3.33-4.26.

Body elongated, white. Rostrum rather slender, about three times as long as wide, reaching almost up to mesocoxae. Antennae slender and elongated. Pronotum 1.8 times as wide as long. Urogomphi (ur) slender and rather elongated, conical, with sclerotised apex, reaching outline of the body, directed downward (Figure 14A-C ).

Chaetotaxy well developed, setae rather short. Head capsule with one vs, two sos equal in length, two os equal in length. Rostrum with one rs and one sls (Figure 14A ). Pronotum with two as, one ds, two sls, two ls, and three pls (Figure 14A-C ); equal in length (Figure 14B ). Setae on head and rostrum as long as those on prothorax. Dorsal parts of meso- and metathorax with two setae different in length placed medially. Abdominal segments I-VIII with two medium setae laterally and three medium setae ventrally, distributed in regular lines. Dorsal parts of abdominal segments I-VII with five setae (d1 placed anteromedially, d2-4 posteromedially and d5 located posterolaterally); abdominal segment VIII with only four very long setae dorsally. Abdominal segment IX with two micro-setae ventrally.

Biological notes.

This species is associated with some Plantago species ( P. lanceolata L., P. lagopus L., P. media L.) ( Hoffmann 1958; Sprick 2001). In west Palearctic larvae are most frequently found in the roots of P. lanceolata , boring channels in upper part of the root crown. Larger roots may inhabit several larvae. Pupation takes place during early summer in the pupal chamber situated in the upper part of larval channel. After emergence, adults overwinter in the soil litter nearby host plant.

Remarks and comparative notes.

This species is very common and widespread in the Palearctic region. It was also reported in North America ( O’Brien and Wibmer 1982). The adult is distinctly variable in the size and shape of the body and vestiture within the same population. It differs from M. circulatus by the black integument and ventrite 5 in the male bearing a median tuft of hair. In larvae, the pronotum has eleven prns instead of eight, the pedal lobes have five pda instead of three, the anal lobes with two ts instead of one, the head with four pes instead of five, the mandible with one mds instead of two, the mala with five vms instead of four, and the prms are longer. The pupae also differ from those of M. circulatus by a different number of setae on head, pronotum and abdominal segments I-VII (see key to the pupae). However, morphological and molecular studies (I. Toševski, unpublished data) demonstrate a clear relationship between M. pyraster and M. circulatus .

Figures

Figure 13. Mecinus pyraster mature larva, habitus and chaetotaxy A habitus of the body and frontal view of the head B lateral view of thoracic segments C lateral view of abdominal segment I D lateral view of abdominal segments VII-X. Abbreviations: Th. I-III - number of thoracic segments, Abd. I-X - number of abominal segments, setae: as - alar, ds - dorsal, eps - epipleural, eus - eusternal, lsts - laterosternal, pda - pedal, pds - postdorsal, prns - pronotal, prs - prodorsal, ps - pleural, ss - spiracular, sts - sternal, ts - terminal.

Figure 14. Mecinus pyraster mature larva, head and mouth parts A head, frontal view B antenna C clypeus and labrum, dorsal view D epipharynx E left mandible F maxillolabial complex, ventral aspect. 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, ligs - ligular, lrs - labral, ls - lateral epicranial, mbs - malar basiventral, mds - mandibular, mes - median, mxps - maxillary palp, pes - postepicranial, ves - ventral, pfs - palpiferal, pms - postlabial, prms - prelabial, stps - stipal, vms - ventral malar.

Figure 15. Mecinus pyraster pupa habitus and chaetotaxy A ventral view B lateral view C dorsal view. Abbreviations: Th. I-III - number of thoracic segments, Abd. I-IX - number of abdominal segments, ur - urogomphi, setae: as - apical, d - dorsal, ds - discal, fes - femoral, l, ls - lateral, os - orbital, sls - postantennal, pls - posterolateral, rs - rostral, sls - superlateral, sos - superorbital, vs - vertical.