Mecinus pirazzolii (Stierlin, 1867)

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 pirazzolii (Stierlin, 1867)

Material examined.

20 L3 larvae and 10 pupae, Serbia, Veliko Gradište, 14.07.2017, 44°45.039'N, 21°31.426'E, 86 m., ex Plantago arenaria , lgt. I. Toševski. Accession numbers of sequenced specimens MN992011 (larva), MN992012 (pupa).

Description of mature larva

(Figures 7A-D , 8A-F ). Measurements (in mm). Body length: 1.40-2.00. Body width (metathorax): 0.73-1.00. Head width: 0.36-0.40.

Body (Figure 7A-D ) white, slender, curved. Chaetotaxy of thoracic segments relatively well developed, setae capilliform, different in length, light yellow; on abdominal segments almost invisible (except dorsal parts of abdominal segments IX and X). Prothorax (Figure 7B ) with eight prns of unequal length (seven relatively long and one medium), two relatively long ps and one short eus. Meso- and metathorax (Figure 7B ) with one medium prs, two long pds, equal in length, one long as, three ss different in length (two relatively long, one short), one long eps, one long ps and one short eus. Pedal area with five long pda, equal in length. Abdominal segments I-VIII (Figure 7C, D ) with one very short prs, three short pds (on segment VIII medium, equal in length), arranged along posterior margin, two minute ss, one short eps, one short ps, one short lsts and two short eus. Abdominal segment IX (Figure 7D ) with three medium ds, all located close to posterior margin, one short ps and two short sts. Each of anal lobes with one minute seta.

Head capsule (Figures 7A , 8A-C ) light white, almost rounded. Des1,3,5 long; des2 two times shorter than des1; des4 three times shorter than des1. Fs4,5 equal in length, almost as long as des1. Les1 medium, les2 long; one very short ves, and one pes (Figure 8A ). Antennae (Figure 8B ) with conical, elongated sensorium (Se), four times as long as wide, and three sensilla basiconica. Clypeus (Figure 8C ) trapezium-shaped, anterior margin slightly concave; cls2 short; clss situated close to cls2. Labrum (Figure 8C ) narrow, trapezium-shaped, anterior margin slightly sinuate; lrs1 long, lrs2 medium lrs3 short. Epipharynx (Figure 8D ) with three finger-like als of almost equal length; two medium finger-like ams; two short finger-like mes; surface smooth; labral rods very short, rounded. Mandibles (Figure 8E ) conical, rather wide, with a small protuberance in the middle of the cutting edge; both mds capilliform, medium, equal in length, placed transversely. Maxilla (Figure 8F ) with one stps and two pfs of equal length; mbs short; mala with six long rod-like dms of almost equal size, five vms different in length. Maxillary palpi: basal palpomere distinctly wider and longer than distal. Prelabium (Figure 8F ) cup-like with one long prms; ligula with two short ligs; premental sclerite clearly visible, cup-shaped, posterior extension with acute apex. Postlabium (Figure 8F ) with medium pms1, medium pms2, and short pms3.

Description of pupa

(Figure 9A-C ). Measurements (in mm). Head width: 0.33-0.40. Body width: 0.93-1.16. Body length: 1.63-2.10.

Body stout, slightly curved, white. Rostrum slender, very short, tapering to its top. Antennae moderately elongated. Pronotum 2.0 times as wide as long. Urogomorpi (ur) very short, conical, not reaching outline of the body (Figure 9A-C ).

Chaetotaxy almost invisible, all setae minute, possible to observation only under higher magnification. Head with one os. Rostrum with one rs placed medially (Figure 9B ). Pronotum with two as, one ls, one ds and three pls. Dorsal parts of meso- and metathorax with two setae placed laterally. Dorsal parts of abdominal segments I-VIII with three setae situated posterolaterally and one seta laterally. Abdominal segment IX without setae.

Biological notes.

This species is associated with the annual plant Plantago arenaria Waldst. & Kit. The adult aggregation on plants is followed by the appearance of flowering stems with spikes in late spring. The females lay one egg onto the base of the pistil or the initialised seed. The act of oviposition is followed by proliferative growth of the ovarian tissue in the form of gall but without changes in the external morphology of the pyxidium. During development, the larvae consume all the tissue inside the pyxidium, leaving only the fruit shell intact. The larvae pupate inside the fruit shell, from which adults emerge after being completely sclerotised. Overwintering takes place in the soil litter near the host plant (I. Toševski, pers. obs.). Sympatric occurrence with M. ictericus is common ( Caldara and Fogato 2013).

Remarks and comparative notes.

This species is distributed in eastern Central Europe, southeastern Europe and Turkey. In our keys, this species is closer to the species of the M. pascuorum group than to others, as already discussed in the Remarks for the group.

Figures

Figure 7. Mecinus pirazzolii 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 8. Mecinus pirazzolii 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, des - dorsal epicranial, lr - labral rods, 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 9. Mecinus pirazzolii 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.