Tychius (s. str.) depressus Desbrochers, 1873

Skuhrovec, Jiří, Gosik, Rafał & Caldara, Roberto, 2014, Immatures of Palaearctic species of the weevil genus Tychius (Coleoptera, Curculionidae): new descriptions and new bionomic data with an evaluation of their value in a phylogenetic reconstruction of the genus, Zootaxa 3839 (1), pp. 1-83 : 12-13

Tychius (s. str.) depressus Desbrochers, 1873

Caldara 1990: 147.

Material examined. 2 larvae from pods of Medicago polymorpha collected 20.v.1979 at Fertilia , Sassari, Sardinia ( Italy), leg. R. Caldara, and 2 pupae obtained from larvae collected contemporaneously together with the others, all determined by association with reared adults.

Differential diagnosis. See Tables 2 and 3 .

Description of mature larva. COLORATION. Head brown to dark yellow. All thoracic and abdominal segments light yellow.

HEAD CAPSULE AND MOUTH PARTS. Head width: 0.44–0.48 mm (see Table. 1 ). Endocarinal line present, relatively short. Des 1 located almost in central parts of epicarnium; des 2 located very near frontal suture, near des 3; des 3 located along frontal suture; des 4 absent; des 5 located anterolaterally; des 2 4 times shorter than others (des 1, des 3, des 5) ( Fig. 60 ). Fs 1 and fs 2 absent; fs 3 short, located posteromedially; fs 4 located anteromedially (along epistoma); fs 5 located anterolaterally (along epistoma), 3 to 4 times longer than fs 3 ( Fig. 60 ). Les almost equal in length as des 3. Ves very short. Post-epicranial area with 2 minute pes. Antennal segment membranous, bearing conical sensorium and 4 very short, conical, sensilla ( Fig. 63 ).

Labrum ( Fig. 64 ) approximately 3 times as wide as long; lms 1 and lms 2 longer than lms 3; anterior margin slightly curved inside. Clypeus ( Fig. 64 ) 3.5 times as wide as long; with 2 pairs of short cls different in length, and 1 sensillum, all located posterolaterally; anterior margin slightly rounded. Epipharynx ( Fig. 65 ) with 2 pairs of als, almost of equal length; with 2 pairs of short ams, ams 1 distinctly longer than ams 2, with 2 long finger-like and 1 short mes; labral rods relatively long, kidney-shaped, converging posteriorly. Mandibles ( Fig. 62 ) with 2 short mds, almost of equal length. Maxilla ( Fig. 61 ): stipes with 1 stps, with 2 pfs of equal length, and 1 mbs, distinctly shorter than pfs, and 1 sensillum; mala with 4 slightly curved dms, different in length; with 3 vms, short and almost of equal length. Maxillary palpi: length ratio of basal and distal palpomeres 1:1.6; basal palpomera with 1 short mpxs; distal palpomera with group of 3–4 conical, cuticular apical processes. Prementum ( Fig. 61 ) almost rounded, with 1 prms; margin of ligula rounded; ligula with 1 lig; premental sclerite distinct. Postmentum ( Fig. 61 ) with 3 pairs of pms, almost of equal length.

THORAX AND ABDOMEN. Body length 3.7–4.3 mm (see Table. 1 ), elongate. Abdominal segments I–VI almost of equal length ( Fig. 66 ). Spiracles on abdomen in anteromedian parts of segments (abdominal segments I–VIII).

Chaetotaxy of body reduced. Setae moderately short or very short, and light yellow. Thorax. Prothorax ( Fig. 67 ) with 9 prn, 6 macro- and 3 microsetae; 2 moderately long ps of same length; 1 eus. Meso- and metathorax ( Fig. 67 ) with 1 prs; 3 pds, different in length; alar area with 1 as; 1 ss; 1 eps; 1 ps; and 1 short eus. Each pedal area of thoracic segments well-separated and with 3 pda, different in length (long, moderately long, short). Abdomen. Abdominal segments I–VII ( Fig. 68 ) with 1 prs; 2 pds of different length; 2 ss of different length; 1 eps; 1 ps; 1 lsts; and 2 short eus. Abdominal segment VIII ( Fig. 69 ) with 1 prs; 1 pds;. 2 ss of different length; 1 eps; 1 ps; 1 lsts; and 2 short eus. Abdominal segment IX ( Fig. 69 ) with 1 ds; 1 ps; and 1 sts. Each anal lobe on abdominal segment X ( Fig. 69 ) with 1 very short, feebly visible seta.

Description of pupa. COLORATION. Body salmon.

MORPHOLOGY ( Figs 70–72 ). Body length 2.4–2.6 mm; widest part 1.2–1.3 mm (see Table. 1 ). Body rather stocky. Rostrum moderately long, approximately 4 times as long as wide, reaching mesocoxae. Pronotum 1.8 times as wide as long.

CHAETOTAXY ( Figs 70–72 ). Setae distinct, moderately long, unequal in length, light brown; on pronotum and head placed on small protuberances. Head capsule including 1 vs, 1 os, and 1 pas. Rostrum without setae. Vs as long as setae on pronotum, distinctly longer than os and pas. Pronotum with 2 as, 1 ls, 1 ds, and 1 pls; ds distinctly smaller than other setae on pronotum. Dorsal parts of meso- and metathorax with 1 seta. Each apex of femora with 1 fes. Setae on abdominal segments I–VIII placed medially and laterally; all abdominal setae located on small, conical protuberances. Pseudocerci short, slightly curved inside.

Biological observations. Only 5 % of collected pods were infested by larvae. Also the adults were not numerous on the flowering plants. Pupation was observed 8 days after the introduction of the larvae in the soil. Adults were observed in the cells 10 days later and emerged after a few days.

Remarks. Tychius depressus is an uncommon species known from central and southern Italy, Sicily, Sardinia, Corsica and northern Africa. It seems monophagous on Medicago polymorpha L. since it was collected on the same plant also in central Italy ( Caldara 1990). The T. depressus group is composed of six species distributed in the eastern Mediterranean region and in Southwestern Asia. There are no biological data on the other five species of the group.

Figures

FIGURES 60–65. Tychius depressus mature larva head, antenna and mouth parts: 60—dorsal view (des—dorsal epicranial s., fs—frontal epicranial s., les—lateral epicranial s., ves—ventral epicranial s., pes—posterior epicranial s., st—stemmata, at—antenna); 61—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.); 62—right mandible (mds—mandible dorsal s.); 63—antenna; 64—labrum and clypeus (cls—clypeal s., lms—labral s.); 65—epipharynx (ams—anteromedial s., als—anteriolateral s., mes—median s., lr—labral

FIGURES 66–69. Tychius depressus mature larva habitus: 66—lateral view, 67—lateral view of thoracic segments, 68—lateral view of abdominal segment I., 69—lateral view of abdominal segments VIII–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.).

FIGURES 70–72. Tychius depressus pupa habitus: 70—ventral view, 71—dorsal view, 72—lateral view (vs—vertical s., os—orbital s., pas—postantennal s., as—apical s., ls—lateral s., ds—discal s., pls—posterolateral s., fes—femoral s., pc—pseudocerci).