Mecinus heydenii Wencker, 1866

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 heydenii Wencker, 1866

Material examined.

4 L3 larvae and 6 pupae, Serbia, Negotin, 1.07.2017, 44°16.610'N, 22°30.480'E, 71 m., ex L. vulgaris , lgt. I. Toševski. Accession numbers of sequenced specimen MN992002.

Description of mature larva

(Figures 28A-D , 29A-F ). Measurements (in mm). Body length: 2.16-2.66. Body width (metathorax or abdominal segments I-II): 0.83-1.00. Head width: 0.30-0.33.

Body (Figure 28A-D ) white-yellowish, very slender. Chaetotaxy weakly developed, setae (except pronotum and dorsal part of abdominal segment IX) extremely short, difficult to observe. Prothorax (Figure 28B ) with four medium and four very short prns, two very short ps and one very short eus. Meso- and metathorax (Figure 28B ) with one short prs, three short pds, one very short as, three minute ss, one very short eps, one very short ps and one very short eus. Pedal area with four very short pda. Abdominal segments I-VIII (Figure 28C, D ) with one very short prs, three very short pds arranged along the posterior margin, two minute ss, two very short eps, one very short ps, one very short lsts and two very short eus. Abdominal segment IX (Figure 28D ) with two ds (one medium and one 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 28A , 29A-F ) pale yellow, distinctly narrowed bilaterally. Frontal suture poorly visible. Des1-3,5 very long, equal in length; des4 four times shorter than other des1. Fs1 and fs2 absent, fs3 very short, fs4 and fs5 long. Les1 shorter than les2; two ves and four pes short (Figure 29A ). Antennae (Figure 29B ) with sensorium (Se) conical, thrice as long as wide, and three sensilla of different types: one sa and two sb. Clypeus (Figure 29C ) trapezium-shaped, anterior margin slightly concave; cls2 relatively long; clss clearly visible. Labrum (Figure 29C ) with sinuate anterior margin; lrs1 long, lrs2 slightly shorter than lrs1, lrs3 two times shorter than lrs1. Epipharynx (Figure 29D ) with three medium, finger-shaped als of almost equal length; two rod-like, different in length ams; two finger-like mes of medium length; surface smooth; labral rods close to kidney-shaped. Mandibles (Figure 29E ) conical, wide, with a small protuberance in the middle of the cutting edge; both mds capilliform, medium, equal in length, placed mediolaterally. Maxilla (Figure 29F ) with one stps and two pfs long, of equal length; mbs very short; mala with six finger-like dms different in length (dms1,2 medium, dms3-6 long to very long), five vms different in length. Maxillary palpi: basal palpomere distinctly wider than distal, both of almost equal length. Prelabium (Figure 29F ) almost rounded with one very long prms; ligula with two ligs different in length; premental sclerite clearly visible, U-shaped. Postlabium (Figure 29F ) with short pms1, long pms2, and short pms3.

Description of pupa

(Figure 30A-C ). Measurements (in mm). Head width: 0.30-0.60. Body width: 0.73-1.13. Body length: 2.33-2.93.

Body elongated, white. Rostrum slender, about five times as long as wide, but reaching up only to procoxae. Antennae slender and elongated. Pronotum 1.4 times as wide as long. Urogomphi (ur) very short, conical, with sclerotised apex, reaching outline of the body, directed downward (Figure 30A-C ).

Chaetotaxy sparse, setae short, unequal length. Head with one os. Rostrum with one rs placed medially. Setae on head and rostrum straight, as long as those on prothorax (Figure 30A ). Pronotum with two as, one ds and three pls. Dorsal parts of meso- and metathorax with three setae placed medially. Abdominal segments I-VIII with one seta laterally and three very short setae ventrally. Dorsal parts of abdominal segments I-VII with five setae (d1 placed anteromedially, d2-4 posteromedially, d5 posterolaterally); segment VIII with four setae dorsally. Abdominal segment IX with two micro-setae ventrally.

Biological notes.

This monophagous species is associated with yellow toadflax, Linaria vulgaris Mill. The adults are active from early spring, following the appearance of the first growing shoots of its host plant. The adults exhibit extreme cryptic behavior, which makes them difficult to collect. Oviposition occurs on actively growing young shoots, usually in the top or middle part of the stem. Females often lay several eggs distributed along the host plant shoot. Oviposition provokes primitive shoot swelling and hypertrophy that leads to the formation of a pseudo-gall of the young shoot. Larval development occurs inside this pseudo-gall, and pupation takes place in larval chambers prepared very close to the stem surface. Emerged adults stay inside the stem until August, when all adults leave their host plant within a two-week period. Overwintering takes place in the soil litter near the host plant.

Remarks and comparative notes.

This species is widely distributed in Europe and is the only one of its group present in northern Europe, from Germany to Sweden. The adult is distinguishable by the rostrum very strongly curved from base to apex, especially before antennal insertion, in both sexes. However, it is somewhat difficult to morphologically separate this taxon from the two cryptic species M. peterharrisi and M. laeviceps . They are well distinguishable, however, by molecular and biological data ( Toševski et al. 2014).

The study of the immatures allowed us to add numerous other interesting differences: larvae of M. heydenii differ from those of M. laeviceps by the pronotum with eight prns (instead of nine), the thoracic segments with three pds (instead of two), each pedal lobe with four pda (instead of three), pds of abdominal segments I-VIII distinctly smaller, and the head with four pes (instead of one). Both species differ from M. peterharrisi by fs1 and fs2 absent and the antennae with two sb (instead of four).

The pupae of the three species are also slightly different in the presence or lack of some setae on the rostrum and pronotum (without sls and ls in M. heydenii and M. peterharrisi , respectively) and femora (with fes in M. heydenii and M. laeviceps ), and their number in the abdominal segments.

Figures

Figure 28. Mecinus heydenii 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 29. Mecinus heydenii 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, clss - clypeal sensorium, des - dorsal epicranial, lr - labral rods, sa - sensillum ampullaceum, sb - sensillum basiconicum, Se - sensorium, st - stemmata, setae: als - anterolateral, ams - anteromedial, cls - clypeal, 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 30. Mecinus heydenii 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, pls - posterolateral, rs - rostral.