Lixus (Ortholixus) bituberculatus Smreczynski , 1968

Trnka, Filip, Stejskal, Robert & Skuhrovec, Jiri, 2016, The morphology of the immature stages of two rare Lixus species (Coleoptera, Curculionidae, Lixinae) and notes on their biology, ZooKeys 604, pp. 87-116 : 89-94

Taxon classification Animalia Coleoptera Curculionidae

Lixus (Ortholixus) bituberculatus Smreczynski, 1968

Description of mature larva.

Measurements (in mm). Body length: 6.5-10.4 (mean 9.2). The widest part of the body (metathorax and abdominal segments I–II) measuring up to 2.8. Head width: 1.4-1.7 (mean 1.5).

General. Body stocky, slightly curved, rounded in cross section (Fig. 7). Cuticle finely spiculate.

Colouration. Head light brown or brown with a distinct pale pattern around the frontal suture (Figs 7, 19). All thoracic and abdominal segments are white with a light brown, elongate stripe on the dorsum of the pronotum (Fig. 7).

Vestiture. Setae on body thin, relatively short, light yellow or orange.

Head capsule (Fig. 1). Head suboval, flattened laterally, endocarinal line long more than half length of frons. Frontal sutures distinct, extended to the antennae. Single stemma (st) in the form of a slightly pigmented spot located anterolaterally on each side. Des1 and des2 located in the upper part of the central part of the epicranium, des1 near the middle part of epicranium, and des2 near the side of the epicranium, des3 located anteriorly near the frontal suture, des4 located in the central part of the epicranium, des5 located anterolaterally; all des long, subequal in length (Fig. 1). Fs1 and fs2 placed medially, fs3 located anteromedially, fs4 located anterolaterally, and fs5 located laterally, close to the epistoma; all setae relatively long, fs4 slightly longer than fs1-3 and fs5 distinctly longer than fs4 (Fig. 1). Les1-2 as long as des1; ves1-2 as long as fs3. Epicranial area with sensilla undistinct.

Antennae located at the end of the frontal suture on each side, membranous and slightly convex basal article bearing one conical triangular sensorium, relatively long; basal membranous article with 5 sensilla different in both shape and length (Fig. 4).

Clypeus (Fig. 2) approximately 2.1 times as wide as long with 2 relatively long cls, almost equal in length, localized posterolaterally and 1 sensillum; anterior margin rounded to the inside.

Mouth parts. Labrum (Fig. 2) approximately 2 times as wide as long, with 3 pairs of piliform lms, of different lengths; lms3 distinctly shorter than very long lms1 and long lms2; lms1 located close to the margin with clypeus, lms2 located anteromedially and lms3 located anterolaterally; anterior margin double sinuate. Epipharynx (Fig. 3) with 4 pairs of blunt, finger-like als, unequal in length, als1-2 distinctly shorter than als3-4; 3 pairs of ams, ams1 and ams2 distinctly shorter than ams3, ams1 and ams2 piliform, and ams3 blunt, finger-like; 2 pairs of short, blunt mes and one sensilla close to mes2, located close to lr; labral rods (lr) elongated, converging anteriorly. Mandibles (Fig. 5) relatively broad, bifid, teeth of unequal height; slightly truncate; both mds relatively long, piliform. Maxilla (Fig. 6) stipes with 1 stps, 2 pfs and 1 mbs; very long stps distinctly longer than long pfs1-2, mbs very short; mala with 12 bacilliform dms of 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 sensilla; length ratio of basal and distal palpomeres: 1:0.7; distal palpomere with one sensillum and a group of conical, apical sensorial papillae. Praelabium (Fig. 6) heart-shaped and distinctly elongated, with 1 relatively long prms; ligula with sinuate margin and 3 piliform micro ligs, unequal in length; premental sclerite well visible. Labial palpi with two palpomeres; length ratio of basal and distal palpomeres: 1:0.7; distal palpomere with one sensillum and short, apical sensorial papillae; basal palpomere with 1 ventral sensillum. Postlabium (Fig. 6) with 3 pms, pms1 located anteriorly, remaining two pairs laterally; relatively long, almost of equal length, pms3 distinctly shorter than pms1 and pms2; surface of postlabium densely covered by distinct asperities.

Thorax. Prothorax distinctly smaller than meso- and metathorax. Metathorax almost of equal length as abdominal segments I–IV. Spiracle bicameral. Prothorax (Fig. 8) with 10 prns unequal in length, 8 of them on weakly pigmented premental sclerite, which is subdivided medially into two triangular plates, next two prns placed below; 2 ps and 2 eus. Mesothorax (Fig. 8) with 1 prs; 4 pds unequal in length, pds2 distinctly shorter than the remaining three setae; 1 short as; 2 short to very short ss; 1 eps; 1 ps and 2 eus. Chaetotaxy of metathorax (Fig. 8) identical to that of mesothorax. Each pedal area of the thoracic segments well separated and pigmented, with 7 long pda, 6 of which on pigmented area, unequal in length.

Abdomen. Abdominal segments I–IV of almost equal length, subsequent abdominal segments decreasing gradually to the terminal parts of the body. Abdominal segment X reduced to four anal lobes of unequal size, the dorsal being distinctly the largest, the lateral pair equal in size, and the ventral lobe very small. Anus located terminally. Spiracles bicameral, the eight abdominal spiracles located laterally, close to the anterior margin of abdominal segments I–VIII. Abdominal segments I–VII (Figs 9-10) with 1 prs; 6 pds, pds3 and pds5 the longest one; 2 ss of unequal length, ss1 very short, ss2 as long as pds6; 2 eps of almost equal length; 2 relatively short ps of unequal length, ps1 very short to minute, ps2 short; 1 lsts and 2 eus. Abdominal segment VIII (Fig. 10) with 1 prs; 4 pds, pds1 and pds6 lacking, pds3 and pds5 less than half of length of the two remaining setae; 2 ss of unequal length, ss1 very short, ss2 long as pds6; 2 eps of almost equal length; 2 short ps of equal length; 1 lsts and 2 eus. Abdominal segment IX (Fig. 10) with 4 ds (ds1 and ds3 very short, ds 2 and ds4 long); 2 short and 1 very short ps and 2 very short to micro sts. Abdominal segment X (Fig. 10) with 2 microsetae and 1 seta (ts) on each lateral anal lobe.

Description of pupa.

Measurements (in mm). Body length: 8.0-10.4 (♂ 8.0-10.4; ♀ 9.8). The widest part of the body, commonly between the apex of the meso- or metafemora: 2.6-3.5.

Colouration. Body white to yellowish (Fig. 20).

Morphology (Figs 11-13, 20). Body stocky, elongated, white or yellowish. Cuticle smooth. Rostrum relatively long, approximately 2.7 to 3.0 times as long as wide, extending beyond the mesocoxae; females with slightly thinner rostrum than males. Antennae relatively long and stout. Pronotum from 1.2 to 1.3 times as wide as long. Mesonotum and metanotum of almost equal length. Abdominal segments I–III of almost equal length; abdominal segment VI semicircular and subsequent 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 (1 specimen) bilobed.

Chaetotaxy (Figs 11-13). Setae relatively short, unequal in length, light yellow or orange, some setae on abdominal segments III–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, rs1 located below antenna, rs2 placed on the anterior margin. Setae on head capsule and rostrum straight, both 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. 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 that of mesothorax. Each femoral apex with 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 their anterior margins. Setae d2-3, d5 and d7 (on abdominal segments IV–VIII) short, thorn-like, located on protuberances; on abdominal segment III only setae d3 and d5. Remaining setae short to very short, hair-like; all setae very short on abdominal segments I–II. 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 7 pairs (d2-8) 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. Urogomphi elongated, triangular.

Biology and ecology.

Habitats. Adults (Fig. 14) prefer dry and sunny habitats such as dry grasslands, meadows often with grazing or mowing (Fig. 21), and road margins with specific disturbance regimes (trampling by movement of cattle or vehicles, etc.).

Adult behaviour. During the day, adults stay among the rosette leaves of the host plant (Fig. 15) near the stem base. Adults were usually observed by sweeping the host plants at night. Data were collected from April to September with the exception of July. The maximum number of records occurred in late summer.

Host plants. Adults and larvae were observed feeding on chicory Cichorium intybus L. ( Asteraceae ), in the studied localities (Fig. 21). Nevertheless, J. Krátký and J. Pelikán (in litt.) also found adult Lixus bituberculatus on Crepis sp. and Picris sp. during night sweeping and a pupa in the root of Picris sp. in Slovakia ( Hajnáčka env. and Bajtava env.).

Life cycle. Lixus bituberculatus is an univoltine species. Adults feed on leaves, but larval development occurs in the basal part of the stem and in the root (Figs 18-19). Females of Lixus bituberculatus bite the lower part of the stem of the host plant near the ground and lay one egg in the hole (Figs 16-17). Usually, only one larva was found to occupy a plant, but rarely, there were two (one in the stem and another in the root crown). Mature larvae were found from July to August. Pupation occurs in the root neck or root (Fig. 20), and fresh adults can be found (inside plants) from middle of August. The exit hole is situated in the upper part of the pupation cell. Adults do not hibernate in the host plants. Most likely, hibernation occurs in the leaf litter, among dry plant debris or in the topsoil.

Rearing of the larvae. For laboratory breeding, 10 mature larvae were collected on August 8th, 2014, but only three pupated under our laboratory conditions. The remaining seven larvae primarily died due to drying of the host plants. The first fresh adult hatched on September 12th and the other two on September 15th, 2014.