Larinus (Larinus) vulpes (Olivier, 1807)

Skuhrovec, Jiri, Volovnik, Semyon & Gosik, Rafal, 2017, Description of the immature stages of Larinusvulpes and notes on its biology (Coleoptera, Curculionidae, Lixinae), ZooKeys 679, pp. 107-137 : 110-117

Larinus (Larinus) vulpes (Olivier, 1807)

Material examined.

UKRAINE: Cyrilivska Spit (locality 3 in Materials and methods), 12-29.viii.2015, 15 larvae, 16 pupae (5♂♂, 11♀♀), leg. S Volovnik.

Description of mature larva.

Measurements (in mm, n = 15). Body length: 13.4-21.2 (mean 18.1). Body width: (meso- and metathorax) 4.03-5.01 (mean 4.46). Head width: 1.99-2.29 (mean 2.14).

General. Body stocky, slightly curved, rounded in cross section (Fig. 7). Cuticle densely spiculate (Figs 8-9).

Colouration. Head light brown or brown with a distinct pale pattern around the frontal and epicranial sutures (Fig. 7). All thoracic and abdominal segments are dark yellow with a light brown, elongate stripe on the dorsum of the pronotum (Fig. 7).

Vestiture. Setae on body thin, short, light yellow or orange (Figs 7-9).

Head capsule (Fig. 1). Head suboval, slightly longer than wide, endocarinal line weak, but long as a half-length of frons. Frontal sutures distinct, wide, and extended to the antennae. Single anterior stemma (st) distinct, in the form of a slightly pigmented spot. 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, nearly subequal in length, except des4 distinctly shorter (Fig. 1). Fs1, fs2 and fs3 placed medially, fs4 located anteromedially, fs4b located laterally close to fs4; and fs5 located anterolaterally, close to the epistoma; all setae very long to long, only fs4b and fs5 medium, distinctly shorter than very long fs1-4 (Fig. 1). Les1-2 and ves1-2 very long, as long as des5. Epicranial area with two sensilla, one upper des1 and the second in upper part of posterior; and also with 3 pes in line with upper des2.

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

Clypeus (Fig. 2) trapezoid-shaped, approximately twice as wide as long, with two relatively long cls, cls2 slightly shorter than cls1, localized posterolaterally and 1 sensillum located close to cls1; anterior margin concave.

Mouth parts. Labrum (Fig. 2) approximately twice 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 bisinuate. Epipharynx (Fig. 3) with 4 blunt, finger-like als, unequal in length, als1-2 shorter than als3-4; 3 ams: ams1 and ams2 distinctly thinner than ams3; ams1 and ams2 piliform, ams3 blunt, finger-like; 2 mes and one sensillum close to mes2; mes1 distinctly smaller than mes2, both located close to lr; labral rods (lr) elongated, slightly diverging on distal half. Mandibles (Fig. 5) relatively broad, bifid, teeth of unequal height; slightly truncate; both mds relatively long, piliform. Maxilla (Fig. 6) stipes with 2 stps, 2 pfs, and 1 mbs; both stps and pfs2 very long and 1.5 times longer than long pfs1, mbs very short; mala with 9 bacilliform dms1-9; 5 short vms1-5, in two sizes: 2 vms short, and 3 very short; all vms distinctly shorter than dms. Maxillary palpi with two palpomeres; basal palpomere with 1 short mxps and two sensilla; length ratio of basal and distal palpomeres: 1:0.9; distal palpomere with one sensillum and a group of conical, apical sensorial papillae. Praelabium (Fig. 6) heart-shaped, with 1 relatively long prms; ligula with sinuate margin and 2 piliform very short ligs, unequal in length; premental sclerite V-shaped clearly visible. Labial palpi with two palpomeres; length ratio of basal and distal palpomeres: 1:0.9; distal palpomere with one sensillum and short, apical sensorial papillae; basal palpomere with 1 ventral sensillum. Postlabium (Fig. 6) with 4 pms, 1 pms located anteriorly, and 3 pms laterally; very long, almost of equal length; surface of postlabium densely covered by distinct asperities.

Thorax. Prothorax larger than meso- and metathorax. Meso- and metathorax distinctly wider than abdominal segments I–IV. Spiracle unicameral. Cuticle densely spiculate and with distinct thorn-like cuticular processes, primarily on dorsal parts but also on pleural parts (Fig. 7). Prothorax (Fig. 10) with ca. 30-35 relatively long to short prns unequal in length, 25 on pigmented pronotal sclerite, which is subdivided medially into two triangular plates, next 5-10 prns placed below; 20 relatively long ps also on pigmented sclerite, and 12 relatively long eus. Mesothorax (Fig. 10) with 3 short prs; 13 relatively long to short pds; 6-7 relatively long to short as; 6 relatively long to short ss on pigmented sclerite; 6-9 relatively long to short eps on pigmented sclerite; 14 relatively long to short ps on pigmented sclerite and 12 relatively long to long eus. Chaetotaxy of meso- and metathorax (Fig. 10) almost identical, but some specimens partly variable in the exact count of setae. Each pedal area of the thoracic segments well separated and pigmented, with 10 long pda on pigmented sclerite, 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 unicameral, the eight abdominal spiracles located laterally, close to the anterior margin of abdominal segments I–VIII. Cuticle also densely spiculate and with distinct thorn-like cuticular processes, primarily on dorsal parts but also on pleural parts (Figs 8-9). Abdominal segments I–VII (Figs 11-12) with 2 relatively long to short prs; 13 relatively long to short pds, 10 pds in line, and 3 pds in the below part partly anteriorly; 7 relatively long to short ss, 5 ss under pds (abdominal segment VII only with 3 setae), and 2 ss in below part of dorsal lobe; 13 (10-14) relatively long to short eps on pigmented sclerite (only on abdominal segments I–II); 9 relatively long ps of unequal length; 2 short lsts and 2 short eus. Abdominal segment VIII (Fig. 12) with 2 relatively long prs; 10 relatively long to long pds in line; 2 relatively long ss in below part of dorsal lobe; 13 relatively long to short eps; 9 relatively long ps of unequal length; 2 short lsts and 2 short eus. Abdominal segment IX (Fig. 12) with 7 ds (6 long ds near posterior margin, and 1 short ds medially); 13 relatively long to long ps; and 2 relatively long and 2 short sts. Abdominal segment X (Fig. 12) with 2 very short setae (ts) on each lateral anal lobe, and 1 very short seta (ts) on dorsal anal lobe.

Description of pupa.

Measurements (in mm; 5 ♂♂, 11 ♀♀). Body length: ♂ 11.8-13.2 (mean 12.5), ♀ 12.6-15.2 (mean 14.0). Body width: ♂ 6.5-7.8 (mean 6.8), ♀ 7.0-8.20 (mean 7.5). Thorax width: ♂ 4.6-4.9 (mean 4.7), ♀ 4.8-5.1 (mean 4.9). Head width: ♂ 1.8-2.0, ♀ 1.9-2.2.

Colouration. All thoracic and abdominal segments light yellow or greenish-white. Cuticle smooth, except thorn-like processes on abdominal segments III–VIII.

Morphology (Figs 13-20). Body moderately slender and elongated. Rostrum long, approximately 2.5 times as long as wide, extended to mesocoxae. Antennae relatively long and slender. Pronotum 2.5 times as wide as long. Meso- and metanotum of equal length. Abdominal segments I–V of equal length, abdominal segments V–VII diminish gradually, abdominal segment VIII almost semi-circular, and abdominal segment IX distinctly smaller than other segments. Urogomphi very short, almond-shaped with acute sclerotised apexes. Spiracles placed dorso-laterally; 5 pairs functional on abdominal segments I–V and one atrophied on abdominal segment VI, on next abdominal segments spiracles invisible. Sexual dimorphism visible in the structure of abdominal segment IX: gonotheca of ♀ divided (Fig. 19), ♂ undivided (Fig. 20).

Chaetotaxy (Figs 13-20). Setae distinct, of different length, light brown. Head capsule includes 1 vertical seta (vs); 3 super-orbital setae (sos1-3) (equal in length); 1 orbital seta (os) and 4 post-antennal setae (pas1-4) (equal in length). Rostrum with 8 rostral setae (rs1-8) (different in length); rs1-4 located apically, rs5-7 latero-apically, and rs8 latero-medially. Mandibular theca with 1 epistomal seta (es). Setae on head capsule and rostrum straight or slightly curved, shorter than setae on pronotum. Pronotum with many setae, which created a characteristic pattern that consisted of: 1 super apical seta (sas), 4 super lateral setae (sls1-4) (equal in length), distributed along a horizontal line, 3 discal setae (ds1-3) equal in length, forming a group medially, and 21 posterolateral setae (pls1-21) (different in length) of which: pls1-11 located along posterior margin of pronotum and next 10 setae (pls12-21) form groups ventrally. Lateral setae in two groups; ls1-5 located more or less along margin of pronotum, next five (ls6-10) form a group (sometimes covered by antennae). Setae on pronotum different in length: pls1-11 the longest, ds1-3 the shortest (Fig. 16). Prolegs with 5 trochanter setae (trs1-5). Mesonotum with 14 setae (d1-14): d1-3 located anteromedially, d4 posteromedially and d5-14 mediolaterally. Metanotum with 14 setae (d1-14): d1-3 located anteromedially, d4-14 form a line medially (Fig. 16). Apex of femora with 3 or 4 long femoral setae (fes) (Fig. 18). Setae on abdominal segments various in size, sometimes replaced by thorn-like cuticu lar processes; a reason the exact number of setae remained difficult to precisely determine. Approximately 40 setae are on dorsal parts of each of abdominal segments I and II, and approximately 30 on each of abdominal segments III–VIII. Generally: 4-6 very short setae placed along anterior margin of each segment, next 20 long and short setae (or ca. 10 long setae and ca. 10 thorn-like cuticular processes) form a regular, horizontal line on median parts; next approximately 15 thin setae form groups dorsolaterally on each segment. Some small setae are replaced by thorn-like cuticular processes, which increase gradually from abdominal segment III to VII. Cuticular processes on abdominal segment VIII distinctly smaller than those on abdominal segments VI and VII. Abdominal segment VIII with 5 small setae along anterior margin, 6 medium size setae and some small cuticular processes medially. Abdominal segments I–VIII with approximately 20 thin setae (l1-20) laterally (Fig. 18); ventral parts of abdominal segments I–VIII with 3 setae located medially or medio-laterally. Abdominal segment IX with 5 short setae, located ventrally along anterior margin of segment, and next single seta on gonothecae. External parts of urogomphi are densely covered by thin setae.

Comparison with larvae of other Larinus species.

To date, larvae of 16 Larinus species have been described ( Gardner 1934; Scherf 1964; Lee and Morimoto 1988; Nikulina et al. 2004; Zotov 2009a, 2010; Gosik and Skuhrovec 2011; Nikulina and Gültekin 2014), while detailed descriptions of the pupae are known for only 8 Larinus species ( Zotov 2009a, 2010; Gosik and Skuhrovec 2011; Nikulina and Gültekin 2014). The comparison with previously described immatures of some other species, primarily of L. (Phyllonomeus) saussureae Marshall, 1924 ( Gardner 1934), L. (Phyllonomeus) carlinae (Olivier, 1807) (as L. planus F.) and L. (Phyllonomeus) iaceae (Fabricius, 1775) (both in Scherf 1964), was somewhat problematic because of missing details of chaetotaxy and/or absence of quality drawings; therefore, a comparison of these three species with other known Larinus species was not possible to the level of detail required to incorporate them in the key (see Key to the immature stages of the Larinus ). Lee and Morimoto (1988) provide a general larval description of the genus Larinus based on two species: L. (Phyllonomeus) latissimus Roelofs, 1873 and L. (Phyllonomeus) meleagris Petri, 1907. However, they did not present any differences between these two species (see aggregation of both species in the key at dichotomy 12).

According to May (1993), the increased number of pds on the meso- and metathorax and abdominal segments I–VII and of setae on the epipharyngeal lining (als) (i.e., more than the most frequent number of setae in weevils) are diagnostic of the mature larva of the subfamily Lixinae. The following descriptions of mature larvae from the tribe Lixini confirmed this diagnosis: genus Larinus ( Scherf 1964; Lee and Morimoto 1988; Nikulina et al. 2004; Zotov 2009a, 2010; Gosik and Skuhrovec 2011; Nikulina and Gültekin 2014); genus Lixus ( Scherf 1964; Lee and Morimoto 1988; May 1994; Nikulina 2001, 2007; Zotov 2009a, b; Nikulina and Gültekin 2011; Gosik and Wanat 2014; Skuhrovec and Volovnik 2015; Trnka et al. 2016); and Rhinocyllus conicus ( May 1994), in addition to descriptions of all known species from the tribe Cleonini ( Zotov 2011; Stejskal et al. 2014; Trnka et al. 2015). For a proper comparison of both tribes, including a key and detailed generic studies, further descriptions of immature stages of several Cleonini would be required.

Gosik and Wanat (2014), in a precise general description of the larvae of the tribe Lixini , summarized the tribe by 16 character sets (for details, see Gosik and Wanat 2014), but some of these characters (primarily chaetotaxy on the body) do not correspond exactly with most Larinus species from the nominotypical subgenus, including the recently described L. vulpes . The species from the subgenus Larinus (except L. idoneus Gyllenhal, 1835 and L. latus (Herbst, 1783)) had very high counts of larval body setae; e.g., pronotum with more than 25 setae and postdorsum on meso- and metathorax and also on abdominal segments I–VII with more than 12 setae (see details in Key to the immature stages of the Larinus and Table 1). The pupal number of setae was identical to that of all known pupae of species from the subgenus Larinus (except L. idoneus ) with a pronotum with 25 or even more setae (see details in Key to the immature stages of the Larinus and Table 2). Morphological characters of larvae and pupae distinctly separated the subgenus Larinus from the other subgenera Phyllonomeus Gistel, 1856 and Larinomesius Reitter, 1924. Only two species ( L. idoneus and L. latus ) from the nominotypical subgenus did not correspond with the described chaetotaxy, which could be explained considering three hypotheses: (1) the nominotypical subgenus can be divided into two distinct groups, (2) these two species do not belong in this subgenus, or (3) these species show a peculiar autapomorphy; a change in a setal number can be a mere convergence (or coincidence). To solve this problem further morphological and molecular studies would be necessary.

The immature stages of L. vulpes had the closest affinity to the larvae of L. (L.) inaequalicollis Capiomont, 1874 and L. (L.) capsulatus Gültekin, 2008 based on five larval morphological characters: (1) frons with 6 or 7 fs; (2) postlabium with 4 or 5 setae; (3) stipes with 2 long sts; (4) prodorsum on meso- and metathorax with 3 prs; and (5) dorsal part of body distinctly spiculate; and two pupal morphological characters: (6) cuticle around setae dark-pigmented, visible spots formed; and (7) rostrum with 3 pas and only 1 rs. The primary differences between L. vulpes and L. inaequalicollis were as follow (see key to the immature stages of the Larinus ): postepicranial setae pes1-pes2 distinct (versus L. inaequalicollis very small, indistinct); frons with 6 fs (versus with 7 fs); endocarina not distinct, its length is as half-length of frons or less (versus distinct, massive, approximately 2/3 the length of frons), and ligula with 2 very thin ligs (versus with 1 micro ligs and two sensillae). The primary differences between L. vulpes and L. capsulatus were are as follows (see key to the immature stages of the Larinus ): postlabium with 4 setae (versus L. capsulatus with 5 setae); meso- and metathorax with 6-7 as, 6 ss and 6-9 eps (versus with 4 as, 4 ss and 5 eps); abdominal segments I–VII with fewer than 14 pds and more than 10 eps (versus more than 15 pds and 8 or fewer eps); and lateral lobe of abdominal segment X with 2 setae (versus 3 setae).

Moreover, detailed descriptions of immature stages of Larinus species are also important for further studies on generic and evidently also subgeneric taxonomic relationships within Lixini and to effectively protect endangered species and promote the use of larvae of Larinus species as potential biological control agents against weeds (e.g., Carduus , Cirsium , Echinops ). Species identification of larvae with morphological evidence is relatively easy, and it is generally much cheaper than identification by molecular methods ( Hirsch et al. 2010). The largest problem in the identification of the immature stages is the relatively low number of available larval descriptions in comparison to the many species only known at the adult stage. However, the problem is not exclusive to Curculionidae , being common to many other beetle groups.