Lixus (Dilixellus) neglectus Fremuth, 1983

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 : 94-100

Taxon classification Animalia Coleoptera Curculionidae

Lixus (Dilixellus) neglectus Fremuth, 1983

Description of mature larva.

Measurements (in mm). Body length: 10.5-13.5 (mean 12.5). The widest part of the body (metathorax and abdominal segments I–II) measuring up to 3.3. Head width: 1.8-2.1 (mean 2.0).

General. Body stocky, slightly curved, rounded in cross section (Fig. 28), densely covered by distinct asperities (mainly dorsal and ventral parts). Cuticle finely spiculate.

Colouration. Head light brown or brown (Figs 28, 38). All thoracic and abdominal segments are white with a light brown elongate stripe on the dorsum of the pronotum (Fig. 28).

Vestiture. Setae on body thin, relatively long to very long, light yellow or orange.

Head capsule (Fig. 22). 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 the 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. 22). Fs1 and fs2 placed medially, fs3 located anteromedially, fs4 located anterolaterally, and fs5 located laterally, close to the epistoma; all setae long to extremely long, fs1 extremely long, fs4 and fs5 very long, distinctly longer than fs2 and fs3, but shorter than fs1 (Fig. 22). 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 3 sensilla different in both shape and length (Fig. 25).

Clypeus (Fig. 23) approximately 2.5 times as wide as long with 2 long cls, almost equal in length, localized posterolaterally and 1 sensillum; anterior margin rounded to the inside; median part covered by thorn-shaped asperities.

Mouth parts. Labrum (Fig. 23) approximately 3 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 placed close to the margin with clypeus, lms2 located anteromedially and lms3 located anterolaterally; anterior margin double sinuate. Epipharynx (Fig. 24) with 4 pairs of blunt, finger-like als, unequal in length, als1-2 distinctly shorter than als3-4; 3 pairs of ams, ams1 and ams3 distinctly shorter than ams2, ams1 and ams3 piliform, and ams2 blunt, finger-like; 2 pairs of short, blunt mes and one sensilla close to mes2; labral rods (lr) elongated, converging anteriorly, distinctly pigmented. Mandibles (Fig. 26) relatively broad, bifid, teeth of unequal height; slightly truncate; mds1 very long, mds2 distinctly short, piliform. Maxilla (Fig. 27) stipes with 1 stps, 2 pfs and 1 mbs; stps and pfs1-2 very long, almost equal in length, mbs very short; mala with 14 bacilliform dms in two different lengths (1-4 long, blunt and 5-14 very long and blunt, with a tendency to be longer and less blunt); 5 relatively long 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: 1:0.8; distal palpomere with one sensillum and a group of conical, apical sensorial papillae. Praelabium (Fig. 27) 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 the basal and distal palpomeres: 1:0.6; distal palpomere with one one sensillum and short, apical sensorial papillae; basal palpomere with 1 ventral sensillum, and pigmented in the basal part, and the connection with the premental sclerite seems as next palpomere. Postlabium (Fig. 27) with 3 pms, pms1 located anteriorly, remaining two pairs laterally; 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. 29) with 10 prns unequal in length, of which 8 on distinctly pigmented dorsal sclerite that is subdivided medially into two triangular plates, next two prns placed below; 2 long ps located on pigmented sclerite, and 1 eus. Mesothorax (Fig. 29) with 1 long prs; 4 long to very long pds, pds2 distinctly shorter than the remaining three setae (both on weakly pigmented sclerites); 1 very short as; 2 short ss; 1 eps; 1 ps (eps and ps on weakly pigmented sclerites) and 1 eus. Chaetotaxy of metathorax (Fig. 29) identical to that of mesothorax. Each pedal area of the thoracic segments well separated and pigmented, with 7 long pda, of which 4-6 on distinctly pigmented area, unequal in length.

Abdomen. Abdominal segments I–V of almost equal length and 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 30-31) with 1 prs; 5 relatively short pds, pds2 and pds4 on abdominal segment VII less than half of length of the three remaining setae which are twice as long as pds on the previous six abdominal segments; 2 ss of unequal length, ss1 very short, ss2 as long as pds5; 2 eps of unequal length; 2 relatively short ps of equal length; 1 long lsts (eps, ps and lsts on weakly pigmented sclerites) and 2 relatively long eus. Abdominal segment VIII (Fig. 31) with 1 relatively long prs; 2 long to very long pds, pds1-2 and pds4 lacking; 2 ss of unequal length, ss1 very short, ss2 as long as prs; 2 eps of unequal length, eps1 relatively long, eps2 long to very long; 2 relatively short ps of equal length; 1 relatively long lsts (eps, ps and lsts on weakly pigmented sclerites) and 2 relatively long eus. Abdominal segment IX (Fig. 31) with 3 ds (ds1-2 long, ds3 short); 2 very short ps and 2 very short to micro sts. Abdominal segment X (Fig. 31) with 2 microsetae (ts), on each lateral lobe.

Description of pupa.

Measurements (in mm). Body length: 9.4-12.7 (♂ 9.4-12.7; ♀ 10.0) and the widest part of the body, commonly between the apex of the meso- or metafemora: 2.8-3.8.

Colouration. Body yellow (Fig. 39).

Morphology (Figs 32-34, 39). Body stocky, elongated, white or yellowish. Cuticle smooth. Rostrum relatively long, approximately 3.1 to 3.5 times as long as wide and extending beyond the mesocoxae. 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–V of almost equal length; abdominal segment VI semicircular and subsequent abdominal segments diminish gradually to the end of the body. Ab dominal segments VII–IX distinctly smaller than other abdominal segments. Gonotheca (abdominal segment IX) in females (1 specimen) bilobed.

Chaetotaxy (Figs 32-34). 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 placed below antenna, rs2 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, and 1 short seta on ventral side (probably pls5). Dorsal parts of mesothorax with 1 seta located posteromedially, 1 seta located posterolaterally and 4 setae located along the anterior margin. Chaetotaxy of metathorax identical to that of mesothorax. Coxa with 1 very short cs. 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 the anterior margins. Setae d2-7 (on abdominal segments III–V) and setae d2-5 and d7 (on abdominal segments VI–VII) short, thorn-like, located on protuberances. Protuberances on abdominal segment VII distinctly prolongated. Remaining setae relatively short, 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; d7 thorn-like, located on protuberances; remaining setae short. 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 distinctly elongated, hooked, triangular.

Biology and ecology

Habitats. Adults live in dry grasslands and meadows with sandy substrates (wind-blown river sand) (Fig. 41).The meadows are often managed for hay production. Numerous specimens were also found on grassy embankments along roads.

Adult behaviour. Adult beetles (Fig. 35) exhibit diurnal as well as nocturnal activity. During sunny days, they spend almost all of their time hiding among the leaves of the host plant near the ground (Figs 36, 42) and rarely climb to the higher parts of the plant.

Host plants. Adults and their immature stages were observed exclusively on dock, Rumex thyrsiflorus Fingerh. ( Polygonaceae ) (Figs 41-42), in all of our localities. In the past, this species was only recorded from garden sorrel ( Rumex acetosa ) L. (e.g., Fremuth 1983).

Life cycle. Lixus neglectus is an univoltine species. Adults feed on leaves, and larvae are stem and root borers (Fig. 38). Females of Lixus neglectus bite the lower part of the stem and lay one egg in the hole (Fig. 37). Larvae feeding in the root produce orange feeding frass (Fig. 37), which is thrown out of the host plant, and its presence is a reliable indication that the plant root is occupied by a larva. One plant is most likely occupied by only one larva. Mature larvae were found from July to August. Pupation takes place in the root neck (Fig. 39), and freshly hatched individuals can be found (inside plants) beginning in the middle of August (Fig. 40). Adults do not hibernate in the host plants, so hibernation most likely occurs in the leaf litter, among dry plant debris or in the topsoil.

Rearing of the larvae. For laboratory breeding, 15 mature larvae were collected on July 13th, 2014, but only two of them pupated in our laboratory conditions. The remaining larvae died primarily due to drying of the host plants. Both of the adults hatched on July 30th.