Lixus (Eulixus) canescens Steven, 1829

Skuhrovec, Jiří & Volovnik, Semyon, 2015, Biology and morphology of immature stages of Lixus canescens (Coleoptera: Curculionidae: Lixinae), Zootaxa 4033 (3), pp. 350-362 : 352-356

Lixus (Eulixus) canescens Steven, 1829

Material examined. UKRAINE: SE of Fedotova Spit located between Sea of Azov and Utlyuk Estuary (46°17'53"N, 35°18'13"E); part of Priazovskyi National Nature Park, 11.v.2014, 2.vii.2014, 10.viii.2014, 15.viii.2014 (9 larvae, 15 pupae (8 ♂, 7 ♀), leg. S. Volovnik.

Description of mature larva. COLOURATION. Head light brown or brown with a pale distinct pattern around the frontal suture (Fig. 5C). All thoracic and abdominal segments are white, only the dorsum of the pronotum with light brown elongate stripe (Fig. 5C). Cuticle finely spiculate.

HEAD CAPSULE AND MOUTH PARTS. Head width: 2.2–2.7 mm (mean 2.5 mm), suboval, flattened laterally, endocarinal line long exceeded to half of frons. Frontal sutures distinct, extended to antennae. Single stemma (st), in the form of a dark pigmented spot, located on each side anterolaterally. Des1 and des2 located in upper part of the central part of epicranium, des1 near to the middle part of epicranium, and des2 near to side of epicranium, des3 located anterially near to frontal suture, des4 located in the central part of epicranium, des5 located anterolaterally; all des long, almost all equal in length ( Fig. 1 A). Fs1 and fs2 placed medially, fs3 located anteriomedially, fs4 located anterolaterally, and fs5 located laterally, close to the epistoma; all setae relatively long, fs4 slightly longer than the remaining three setae and fs5 slightly longer than fs4 ( Fig. 1 A). Les1–2 as long as des1; and ves1–2 as long as fs3. Epicranial area without pores. Antennae located at the end of the frontal suture on each side, membranous and slightly convex basal article bearing conical triangular sensorium, relatively long; basal membranous article with 3 sensillae different in both shape and length ( Fig. 1 D).

Clypeus ( Fig. 1 E) approx. 2.5 times as wide as long with 2 relatively long cls, almost equal in length, localized posteriolaterally and 1 sensillum; anterior margin rounded to the inside; median part covered by thorn-shaped cuticular processes. Labrum ( Fig. 1 E) approximately 3 times as wide as long, with 3 pairs of hairform lms, of different length; lms3 distinctly shorter than very long lms1 and lms2; lms1 placed close to the margin with clypeus, lms2 located anteriomedially and lms3 located anterolaterally; anterior margin double sinuate. Epipharynx ( Fig. 1 F) with 3 pairs of blunt, finger-like als, unequal in length; 3 pairs of ams, ams1 and ams2 distinctly shorter than ams3, ams1 and ams3 hair-form, and ams2 blunt, finger-like; 2 pairs of short, blunt mes; labral rods (lr) elongated, converging anterially. Mandibles ( Fig. 1 C) relatively broad, bifid, tooth of unequal height; slightly truncate; both mds relatively short, hairform. Maxilla ( Fig. 1 B) stipes with 1 stps, 2 pfs and 1 mbs, stps and pfs1–2 very long, equal in length, mbs very short; mala with 12 bacilliform dms in two different lengths (6 very long and 6 relatively long); 5 short vms, almost equal in length; vms distinctly shorter than dms. Maxillary palpi with two palpomeres; basal palpomere with 1 very short mxps and two pores; length ratio of basal and distal palpomeres: 1:0.8; distal palpomere with one pore and a group of conical, cuticular apical processes. Praelabium ( Fig. 1 B) heart-shaped and distinctly elongated, with 1 relatively short prms; ligula with sinuate margin and 3 hairform micro ligs, unequal in length; premental sclerite well visible. Labial palpi with two palpomeres; length ratio of basal and distal palpomeres: 1:0.6; distal palpomere with one pore and short, cuticular apical processes; basal palpomere with 1 dorsal pore. Postlabium ( Fig. 1 B) with 3 pms, pms1 located anteriorly, remaining two pairs laterally; very long, almost of equal length, pms3 slightly shorter than pms1 and pms2; surface of postlabium densely covered by distinct cuticular processes.

THORAX AND ABDOMEN. Body length: 12.0–16.0 mm (mean 14.5 mm) stocky, slightly curved, rounded in cross section ( Fig. 2 A). The widest place in the body (metathorax and abdominal segments I–II) measuring up to 5.5 mm. Prothorax distinctly smaller than meso- and metathorax. Metathorax and abdominal segments I–III of almost equal length, next abdominal segments decreasing gradually to the terminal parts of the body. Abdominal segment X reduced to four anal lobes of unequal size, the dorsal lobe being distinctly the largest, the lateral pair equal in size, and the ventral lobe very small. Anus located terminally. Spiracles (9 pairs) bicameral, the first placed between the pro- and mesothorax (see Material and methods), the abdominal spiracles located laterally, close to the anterior margin of abdominal segments I–VIII.

Chaetotaxy of mature larva. Setae thin, relatively long, light yellow or orange. Thorax. Prothorax ( Fig. 2 B) with 10 prns unequal in length, 7 of them on weakly pigmented dorsal sclerite, this sclerite subdivided in two triangular plates medially; 2 ps and 1 eus. Mesothorax ( Fig. 2 B) with 1 prs; 4 pds almost of equal length; 1 short as; 2 short ss; 1 eps; 1 ps and 1 eus. Chaetotaxy of metathorax ( Fig. 2 B) identical to mesothorax. Each pedal area of thoracic segments well separated, with 7 long pda, 4 of them on pigmented pedal area, unequal in length. Abdomen. Abdominal segments I–VII ( Figs 2 C–D) with 1 prs; 6 pds, pds5–6 the longest one, pds3 and pds5 on abdominal segment VII less than half of length of the four remaining setae which are twice as long as pds on the previous six abdominal segments; 2 ss of unequal length, ss1 very short, ss2 long as pds6; 2 eps of almost equal length; 2 relatively short ps of equal length; 1 lsts and 2 eus. Abdominal segment VIII ( Fig. 2 D) with 1 prs; 5 pds, pds1 lacking, pds3 and pds5 less than half of length of the three remaining setae; 2 ss of unequal length, ss1 very short, ss2 long as pds6; 2 eps of almost equal length, 2 relatively short ps of equal length, 1 lsts and 2 eus. Abdominal segment IX ( Fig. 2 D) with 4 ds (ds1–2 and ds4 long, ds3 short); 3 very short ps and 2 very short to micro sts. Each anal lobe on abdominal segment X ( Fig. 2 D) with 1 microseta (ts).

Description of pupa. COLOURATION. Body yellow. MORPHOLOGY ( Figs 3 A–C, 5D–E). Body length: 14.5– 17.3 mm (♂ 14.5–16.0 mm; ♀ 15.5–17.3 mm), at the widest region: 3.9–4.5 mm. The widest place in the body is commonly between the apex of the meso- or metafemora. Body stocky, elongated, white or yellowish. Cuticle smooth. Rostrum relatively short, approximately 2.4 to 3.3 times as long as wide, extended beyond mesocoxae; females with thiner rostrum than males. Antennae relatively long and stout. Pronotum from 1.3 to 1.5 times as wide as long. Mesonotum and metanotum of almost equal length. Abdominal segments I–V of almost equal length; abdominal segment VI semicircular, next abdominal segments diminish gradually to the end of the body. Abdominal segments VII–IX distinctly smaller than other abdominal segments. Gonotheca (abdominal segment IX) in females (7 specimens) divided. Sexual dimorphism in weevils visible mainly in length of rostrum and structure of abdominal segment IX: gonotheca of ♂ undivided, of ♀ divided.

CHAETOTAXY ( Figs 3 A–C). Setae relatively long, unequal in length, light yellow or orange, some setae on abdominal segments II–VIII distinctly stronger and located on protuberances. Setae well visible. Head capsule includes 1 vs, 3 sos, 1 os and 4 pas. Rostrum with 2 rs, located on the anterior margin. Setae on head capsule and rostrum straight, rs and all pas distinctly shorter than the remaining setae on head, thoracic and abdominal segments. Pronotum with 2 as, 2 ds, 2 ls and 4 pls, and 1 short seta on ventral side. Dorsal parts of mesothorax with 1 seta located posteromedially, 1 seta located posterolaterally and 4 setae located along its anterior margin. Chaetotaxy of metathorax identical to mesothoracal. Coxa with 1 very short seta. Each apex of femora with groups of 2 fes. Dorsal parts of abdominal segments I–VIII each with 2 pairs of setae located posteriorly (d1, d9) and 7 pairs (d2–8) located along theirs anterior margins. Setae d2–3, d5 and d7 (on abdominal segments III–VII) short, thorn-like, located on protuberances. Remaining setae relatively long, hair-like. Abdominal segments I–VII with groups of 2 lateral setae and 5 pairs of ventral setae. Dorsal part of abdominal segment VIII with 1 seta located posteriorly (d9) and 5 pairs (d3–7) located along its anterior margin; d3, d5 and d7 thorn-like, located on protuberances; remaining setae elongated. Abdominal segment VIII with groups of 2 lateral setae and 5 short ventral setae. Abdominal segment IX with 2 pairs of ventral microsetae and 1 pair of short, thin setae. Pseudocerci short, triangular.

Comparison with larvae of other Lixus species. Larvae of 19 Lixus and two Hypolixus species have been described so far ( Scherf 1964; Lee & Morimoto 1988; Nikulina 2001, 2007; Zotov 2009a, b; Nikulina & Gültekin 2011; Gosik & Wanat 2014), but a detailed description of the pupa is known for only 7 Lixus species ( Scherf 1964; Zotov 2009a, b; Nikulina & Gültekin 2011; Gosik & Wanat 2014).

At this time, Nikulina (2001) has presented the most precise general larval description of the genus Lixus , which can be summarised by 19 character sets (for details see Nikulina 2001 or Gosik & Wanat 2014). The larva of L. canescens fits all of these characters, with just a few exceptions, partly resulting from differences in terminology (for details see Gosik & Wanat 2014). Nikulina (2001) also published the only comprehensive and known larval key available in this genus. The larva of L. canescens fits most affinities to the larva of L. linnei Faust, 1888 (abdominal segment X with only one seta on dorsal side, mainly on lateral lobes). The differences are as follows: prothoracic tergite with only 7 prn on sclerotised area (vs. 8 prn); clypeus less than twice as wide as labrum; maxilla stipes with short 1 mbs (vs. without mbs (it could be also easily overlooked because it very often minute); prodorsum on abdominal segment IX with only 4 ds (vs. 5 ds), and 3 very short ps (vs. 1 long ps). The precise key and detailed subgeneric study in the genus Lixus is currently not possible because our knowledge of the immature stages is scarce.

May (1993) considered the increased number of pds on meso- and metathorax and abdominal segments I–VII, and the increased number of epipharyngeal lining setae (als) (i.e., higher than the most frequent number of setae in weevils) as diagnostic for the mature larva of the subfamily Lixinae . Descriptions of mature larvae from the tribe Lixini ( Larinus species: Zotov 2009a, 2010; Gosik & Skuhrovec 2011; Lixus species: Scherf 1964; Lee & Morimoto 1988; Nikulina 2001, 2007; Zotov 2009a, b; Nikulina & Gültekin 2011; Gosik & Wanat 2014; Rhinocyllus conicus: May 1994 ) fit this diagnosis, as do all known species from the tribe Cleonini ( Stejskal et al. 2014, Trnka et al. 2015). Gosik & Wanat (2014) compared the larva and pupa of the genera Lixus and Larinus and determined their differential characters. Currently, the comparison of both tribes including key and detailed generic studies are impossible because of our limited knowledge of immature stages. The main problem is that we are unable to divide the morphological characteristics in this group into (i) characteristics useful for phylogenetics and (ii) characteristics useful for species identification. Once this categorisation is complete, it will be possible to use it for future phylogenetic studies.

Figures

FIGURE 1. Lixus canescens mature larva head, antenna and mouth parts: A—dorsal view (des — dorsal epicranial s., fs — frontal epicranial s., les — lateral epicranial s., ves — ventral epicranial s., st—stemmata, at—antenna); B—right maxilla, dorsal view (dms — dorsal malar s., vms — ventral malar s., mpxs — maxillary palps s., mbs — basioventral s., pfs — palpiferal s., stps — stipital s.), prementum and postmentum, ventral view (prms — premental s., pms — postmental s., ligs — ligular s.); C—right mandible (mds — mandible dorsal s.); D—antenna; E—labrum and clypeus (cls — clypeal s., lms — labral s.); F—epipharynx (ams — anteromedial s., als — anterolateral s., mes — median s., lr—labral rods).

FIGURE 2. Lixus canescens mature larva habitus: A—shape of the body (lateral view), B – lateral view of thoracic segments, C—lateral view of abdominal segment II., D—lateral view of abdominal segments VII – X (prns — pronotal s., prs — prodorsal s., pds — postdorsal s., as — alar s., ss — spiracular s., eps — epipleural s., ps — pleural s., pda — pedal s., lsts — laterosternal s., eus — eusternal s., ds — dorsal s., sts — sternal s., ts — terminal s., Th 1 – 3, Ab 1 – 10 — number of segments).

FIGURE 3. Lixus canescens pupa habitus: A—ventral view, B—dorsal view, C—lateral view (vs — vertical s., sos — superorbital s., os — orbital s., pas — postantennal s., rs — rostral s., as — apical s., ls — lateral s., ds — discal s., pls — posterolateral s., cs — coxal s., fes — femoral s., d — dorsal s., l — lateral s., v — ventral s., Th 1 – 3, Ab 1 – 9 — number of segments, pcpseudocerci).