Tychius (s. str.) striatulus Gyllenhal, 1836

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 : 8

Tychius (s. str.) striatulus Gyllenhal, 1836

Caldara 1990: 89.

Material examined. 6 larvae which emerged from pods of Ononis natrix L., collected 3.viii.1992, at Parodi Ligure , Alessandria province, Piemonte (northern Italy), leg. R. Caldara, and one larva which emerged from pods of O. natrix , collected 25.v.1979, on sand dunes at Baratz lake , Sassari province, Sardinia ( Italy), leg. R. Caldara, all determined by association with adults collected on the same plant .

Differential diagnosis. See Table. 2 .

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

HEAD CAPSULE AND MOUTH PARTS. Head width: 0.60–0.75 mm (see Table. 1 ). Endocarinal line present, exceeding middle of frons. Des 1 located almost in central parts of epicarnium; des 2 absent; des 3 located along frontal suture; des 4 absent; des 5 located anterolaterally; all of equal length ( Fig. 11 ). Fs 1 and fs 2 absent; fs 3 short, located medially; fs 4 located anteromedially (along epistoma); fs 5 located anterolaterally (along epistoma), 4 times longer than fs 3 ( Fig. 11 ). Les clearly shorter than des 3. Ves very short. Postepicranial area with group of 3 minute pes. Antennal segment membranous, bearing conical sensorium and 2 finger-like, sensilla ( Fig. 14 ).

Labrum ( Fig. 15 ) approximately 3.5 times as wide as long; lms 1 2 times longer than lms 3, lms 2 distinctly longer than lms 3; anterior margin double sinuate. Clypeus ( Fig. 15 ) 3.2 times as wide as long; with 2 pairs of short cls of same length, and 1 sensillum, all located posterolaterally; anterior margin slightly rounded. Epipharynx ( Fig. 16 ) with 2 pairs of als, different in length; with 2 pairs of short and triangular ams; with 3 relatively short and fingerlike mes; labral rods short, kidney-shaped, slightly converging posteriorly. Mandibles ( Fig. 13 ) with 2 short mds, different in length. Maxilla ( Fig. 12 ): stipes with 1 stps, 2 pfs of different length, and 1 mbs, distinctly shorter than pfs; mala with 4 straight dms, different in length; with 3 vms, moderately long and almost of equal length. Maxillary palpi: length ratio of basal and distal palpomeres 1:1.25; basal palpomera with 1 short mpxs; distal palpomera with group of 2–3 conical, cuticular apical processes. Prementum ( Fig. 12 ) heart-shaped, with 1 prms; margin of ligula slightly rounded, ligula with 1 lig; premental sclerite distinct. Postmentum ( Fig. 12 ) with 3 pairs of pms different in length.

THORAX AND ABDOMEN. Body length 3.4–4.1 mm (see Table. 1 ), elongate. Abdominal segments I–III slightly smaller than abdominal segments IV–VI ( Fig. 17 ). Spiracles on abdomen in anteromedian parts of segments (abdominal seg. I–VIII).

Chaetotaxy of body rather reduced. Setae moderately short or very short and light yellow. Thorax. Prothorax ( Fig. 18 ) with 6 prn; all macrosetae of equal length; 2 moderately long ps of same length; 1 eus. Meso- and metathorax ( Fig. 18 ) with 1 prs; 3 pds, different in length; alar area with 1 very short as; 1 very short ss; 1 eps; 1 ps; and 1 short eus. Each pedal area of thoracic segments well-separated and with 3 pda, equal in length (moderately long). Abdomen. Abdominal segments I–VII ( Fig. 19 ) with 1 prs; 3 pds of different length; 2 ss of different length; 2 eps of different length; 2 ps; 1 lsts; and 2 short eus. Abdominal segment VIII ( Fig. 20 ) with 1 prs; 1 pds; 2 ss of different length; 2 eps of different length; 2 ps; 1 lsts; and 2 short eus. Abdominal segment IX ( Fig. 20 ) with 2 ds of different length; 2 short ps; and 1 sts. Anal lobes on abdominal segment X ( Fig. 20 ) with 3 setae, 2 moderately long and 1 very short, feebly visible seta.

Biological observations. In both localities the collection of the pods was made when only a few of them were ripe and the adults of the species were very numerous on the flowers of the plants and most of them in copula. However after 7–9 days larvae emerged from the pods, that show only a small hole but no other signs of damage. After 12–14 days from collection, the remaining pods were artificially opened and in a few of them died small larvae at first and second instar were found (per cent of collected pods infested 0.5).

Remarks. We did not observe differences in larvae between the specimens from northern Italy and those from Sardinia. It is noteworthy that this species in Sardinia is present in one of the several multicoloured varieties known for the species, the so called variety deliciosus Perris, 1869 that apparently seems to completely replace the unicolorous typical form which similarly lives on O. natrix in the Mediterranean region. Tychius striatulus belongs to a group of four very closely related species, all of which live on Ononis .

Figures

FIGURES 11–16. Tychius striatulus mature larva head, antenna and mouth parts: 11—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); 12—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.); 13—right mandible (mds—mandible dorsal s.); 14—antenna; 15—labrum and clypeus (cls—clypeal s., lms—labral s.); 16—epipharynx (ams—anteromedial s., als—anteriolateral s., mes—median s., lr—labral rods).

FIGURES 17–20. Tychius striatulus mature larva habitus: 17—lateral view, 18—lateral view of thoracic segments, 19—lateral view of abdominal segment I., 20—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.).