Mecinus circulatus (Marsham, 1802)

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 circulatus (Marsham, 1802)

Material examined.

5 L3 larvae and 10 pupae, 1.07.2017, Zemun, Serbia, GPS 44°39.030'N, 21°28.355'E, 162 m., lgt. I. Toševski. Accession number of sequenced specimen MN991999.

Description of mature larva

(Figures 10A-D , 11A-F ). Measurements (in mm). Body length: 2.33-2.73. Body width (metathorax): 0.83-1.06. Head width: 0.50-0.53.

Body (Figure 10A-D ), light yellow, slender, curved (Figure 10B ). Thoracic segments larger than abdominal segment I. Abdominal segments I-VI of almost equal length; 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, transparent, difficult to observe (Figure 10B ). Prothorax (Figure 10B ) with eight prns (six medium and two very short); two medium ps and one very short eus. Meso- and metathorax (Figure 10B ) with one very short prs, two pds (one very short, one medium), one medium as, three ss (two medium and one very short), one medium eps, one medium ps and one very short eus. Pedal area with three pda (one medium and two very short). Abdominal segments I-VIII (Figure 10C, D ) with one very short prs, three pds arranged along the posterior margin (order: very short, medium and very short), two ss different in length, two eps different in length, one medium ps, one medium lsts and two very short eus. Abdominal segment IX (Figure 10D ) with two ds (one medium and one very short), all located close to the posterior margin, one very short ps and two very short sts. Each lateral anal lobe (abd. seg. X) with one minute seta.

Head capsule (Figures 10A , 11A-F ) pale brown, narrowed bilaterally. Frontal suture poorly visible. Des1-3 very long, equal in length, des4 four times shorter than des1, des5 slightly shorter than des1. Fs1 short; fs3 short, fs4,5 long. Les1 and les2 equal in length, slightly shorter than des1; both ves short, and five short pes (Figure 11A ). Antennae (Figure 11B ) with conical sensorium (Se) four times as long as wide, and three sensilla basiconica. Clypeus (Figure 11C ) trapezium-shaped, anterior margin concave; cls1-2 relatively short; clss placed close to cls2. Labrum (Figure 11C ) with distinctly sinuate anterior margin; lrs1 very long, lrs2 slightly shorter than lrs1, lrs3 two times shorter than lrs1. Epipharynx (Figure 11D ) with three medium, finger-shaped als of almost equal length; two rod-like ams, equal in length; one finger-like mes of medium length; surface smooth; labral rods close to kidney-shaped. Mandibles (Figure 11E ) conical, wide, with a small protuberance in the middle of the cutting edge; both mds capilliform, medium, equal in length, placed mediolaterally. Maxilla (Figure 11F ) with one stps and two pfs equal length; mbs very short; mala with six finger-like dms of almost equal size; four vms different in length. Maxillary palpi: basal palpomere distinctly wider and slightly longer than distal. Prelabium (Figure 11F ) cup-like with one relatively short prms; ligula with two ligs different in length; premental sclerite well visible, cup-shaped. Postlabium (Figure 11F ) with medium pms1, long pms2, and medium pms3.

Description of pupa.

(Figure 12A-C ). Measurements (in mm). Head width: 0.46-0.50. Body width: 1.16-1.40. Body length: 2.46-3.00.

Body moderately elongated, white. Rostrum rather short, about 3.2 times as long as wide, reaching up to mesocoxae. Antennae slender and elongated. Pronotum 1.25 times as wide as long. Mesonotum slightly shorter than metanotum. Urogomphi (ur) short, slender, conical, with sclerotised, sharp apex, slightly reaching outline of the body, directed downward (Figure 12A-C ).

Chaetotaxy very sparse, setae short or minute. Head with one vs, one os and one sos. Rostrum with one rs and one pas. Setae on head and rostrum straight, as long as those on prothorax (Figure 12A ). Pronotum with one as, one ls, two sls, and two pls. Dorsal parts of meso- and metathorax with two setae placed medially. Apex of femora with one minute fes (Figure 12A-C ). Dorsal parts of each abdominal segments I-VIII with three setae placed posteromedially along margins of each segments. Abdominal segment IX with two micro-setae ventrally.

Biological notes.

This species is very common on Plantago lanceolata L., while in southeastern Europe, it is also common on some other closely related species, such as P. arenaria (sub P. psyllium L.), P. afra L. (sub P. cynops L.) and P. subulata L. ( Hoffmann 1958; Sprick 2001). The females oviposit in early spring on young growing vegetative shoot buds. Newly hatched larvae bore through the central part of the shoot bud, forming a 1-2 cm long larval channel that rarely rises above the root crown. The larvae pupate inside the larval channel, and the emerged adult leaves the pupa chamber after a short time. The adult overwinters in the soil litter near the host plant.

Remarks and comparative notes.

This is a common species in western, central and southern Europe, northern Africa and the Middle East. By the colour of the elytral integument, with black and reddish vittae, the adults differ from M. pyraster , whose integument is completely black. However, both the study of the morphological characters in adults and immatures and the preliminary molecular study (I. Toševski, unpublished data) agree with the hypothesis of close relationships between these two species.

Larvae are easily separable from those of M. pyraster : the pronotum has eight prns instead of 11, the pedal lobes has three pda instead of five, the anal lobes with one ts instead of two, the head with five pes instead of four, the mandible with two mds instead of one, the mala with four vms instead of five, and the prms are shorter.

Pupae differ from those of M. pyraster by the head with one sos and one os instead of two, the pronotum with a different number of setae in all positions, and the abdominal segments I-VII with three setae dorsally instead of five.

Figures

Figure 10. Mecinus circulatus 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 11. Mecinus circulatus 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, 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 12. Mecinus circulatus 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, fes - femoral, l, ls - lateral, os - orbital, sls - postantennal, pls - posterolateral, rs - rostral, sls - superlateral, sos - superorbital, vs - vertical.