Tychius (s. str.) decretus Tournier 1874

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 : 21-22

Tychius (s. str.) decretus Tournier 1874

Caldara 1990: 193.

Material examined. 1 larva from pods of Trifolium resupinatum L. collected 28.v.1979 at Posada , Nuoro province, Sardinia ( Italy), leg. R. Caldara, and 8 pupae reared 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 or dark yellow. All thoracic and abdominal segments light yellow.

HEAD CAPSULE AND MOUTH PARTS. Head width: 0.38 mm (see Table. 1 ). Endocarinal line present, reaching middle of frons. Des 1 located very near frontal suture; des 2 located mediolaterally; des 3 located along frontal suture; des 4 very short located along frontal suture; des 5 located anterolaterally; des 4 7 times shorter than des 3 and des 5 ( Fig. 164 ). 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. 164 ). Les distinctly shorter than des 3. Ves short. Postepicranial area with group of 4 minute pes. Antennal segment membranous, bearing conical sensorium and without sensillum ( Fig. 167 ).

Labrum ( Fig. 168 ) approximately 2 times as wide as long; lms 1 4–5 times shorter than lms 2, lms 3 some shorter than lms 2; anterior margin doubly sinuate. Clypeus ( Fig. 168 ) 2 times as wide as long; with 1 short cls located posterolaterally; anterior margin slightly rounded. Epipharynx ( Fig. 169 ) with 2 pairs of als, different in length; with 2 pairs of short and triangular ams; with 2 pairs of relatively short and finger-like mes; labral rods relatively long, elongate, strongly converging posteriorly. Mandibles ( Fig. 166 ) with 2 short mds, different in length. Maxilla ( Fig. 165 ): stipes with 1 stps, 2 pfs of different length, pfs 1 distinctly shorter than pfs 2, and 1 mbs, distinctly shorter than pfs 2, and 2 sensilla; mala with 4 straight dms, different in length; with 3 vms, short and almost of equal length. Maxillary palpi: length ratio of basal and distal palpomeres 1:1; basal palpomera with 1 short mpxs; distal palpomera with group of 4 conical, cuticular apical processes. Prementum ( Fig. 165 ) heart-shaped, with 1 prms; margin of ligula rounded, ligula with 1 lig; premental sclerite distinct. Postmentum ( Fig. 165 ) with 3 pairs of pms, almost of equal length.

THORAX AND ABDOMEN. Body length 1.8 mm (see Table. 1 ), moderately elongate. Abdominal segments I–III slightly smaller than abdominal segments IV–VI ( Fig. 170 ). 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. 171 ) with 6 prn; all macrosetae of equal length; 1 moderately long ps; 1 eus. Meso- and metathorax ( Fig. 171 ) with 1 prs; 2 pds, almost of same length; 1 ss; 1 eps; 1 ps; and 1 short eus. Each pedal area of thoracic segments well-separated and with 2 pda. Abdomen. Abdominal segments I–VII ( Fig. 172 ) with 1 prs; 2 pds of different length; 3 very short ss; 1 eps; 1 ps; 1 lsts; and 2 short eus. Abdominal segment VIII ( Fig. 173 ) with 1 prs; 2 pds; 3 very short ss; 1 eps; 1 ps; 1 lsts; and 2 short eus. Abdominal segment IX ( Fig. 173 ) with 1 ds; 1 ps; and 1 sts. Anal lobes on abdominal segment X ( Fig. 173 ) with 1 very short, feebly visible seta.

Description of pupa. COLORATION. Body whitish yellow.

MORPHOLOGY ( Figs. 174–176 ). Body length 1.4–2.4 mm; widest part 0.6–1.1 mm (see Table. 1 ). Body elongate. Rostrum very long, approximately 7 times as long as wide, almost reaching metacoxae. Pronotum 1.4 times as wide as long.

CHAETOTAXY ( Figs. 174–176 ). Setae distinct, short, 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 and os as long as setae on pronotum, distinctly longer than pas. Pronotum with 2 as, 2 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 2 fes. Setae on abdominal segments I–VIII placed medially and laterally; all abdominal setae located on small, conical protuberances. Pseudocerci very short, slightly curved inside.

Biological observations. Pupae were found in the cell 7 days later the larvae entered the soil. The duration of the pupal stage was 12 days. Adults were found walking on the surface 3 days later.

Remarks. The same pods, where larvae of T. decretus were collected, were more extensively parasitized also by larvae of Apion trifolii (Linnaeus, 1758) . In the same field the closely related species T. pusillus was also collected, but living on Trifolium resupinatum (see above).

Figures

FIGURES 164–169. Tychius decretus mature larva head, antenna and mouth parts: 164—dorsal view (des—dorsal epicranial s., fs—frontal epicranial s., les—lateral epicranial s., pes—posterior epicranial s., st—stemmata, at—antenna); 165—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.); 166—right mandible (mds—mandible dorsal s.); 167—antenna; 168—labrum and clypeus (cls—clypeal s.,

FIGURES 170–173. Tychius decretus mature larva habitus: 170—lateral view, 171—lateral view of thoracic segments, 172—lateral view of abdominal segment I., 173—lateral view of abdominal segments VII–X (prns—pronotal s., prs—prodorsal s., pds—postdorsal 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 174–176. Tychius decretus pupa habitus: 174—ventral view, 175—dorsal view, 176—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).