Tychius (s. str.) pusillus Germar, 1842

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 : 23-24

Tychius (s. str.) pusillus Germar, 1842

Caldara 1990: 191.

Material examined. 29 larvae from pods of Trifolium resupinatum L. collected 28.v.1979 at Posada, Nuoro province, Sardinia ( Italy), leg. R. Caldara, and 6 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 yellow. All thoracic and abdominal segments white to whitish yellow.

HEAD CAPSULE AND MOUTH PARTS. Head width: 0.17–0.30 mm (see Table. 1 ). Endocarinal line present, exceeding middle of frons. Des 1 located almost in central parts of epicranium; des 2 located very near frontal suture, near des 3; des 4 absent; des 5 located anterolaterally; des 2 4 times shorter than des 3 and des 5 ( Fig. 190 ). Fs 1 and fs 3 located along frontal suture; fs 2 absent; fs 4 located anteromedially (along epistoma); fs 5 located anterolaterally (along epistoma), 5 times longer than fs 1 and fs 3 and 2 times longer than fs 4 ( Fig. 190 ). Les almost as long as des 3. Ves very short. Post-epicranial area without seta. Antennal segment membranous, bearing conical sensorium and 2 finger-like, sensilla ( Fig. 193 ).

Labrum ( Fig. 194 ) approximately 2.4 times as wide as long; lms 1 3 times longer than lms 3, lms 2 distinctly longer than lms 3; anterior margin doubly sinuate. Clypeus ( Fig. 194 ) 2.5 times as wide as long; with 2 pairs of very short cls of same length, and 1 sensillum, all posterolaterally; anterior margin slightly rounded inside. Epipharynx ( Fig. 195 ) with 2 pairs of als, almost of equal length; with 2 pairs of short and triangular ams; with 2 long fingerlike and 1 short mes; labral rods relatively long, elongate, converging posteriorly. Mandibles ( Fig. 192 ) with 2 short mds, different in length. Maxilla ( Fig. 191 ): stipes with 1 stps, and 2 pfs of equal length; mala with 3 slightly curved dms, different in length; with 2 vms, short 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 3–4 conical, cuticular apical processes. Prementum ( Fig. 191 ) triangular, with 1 prms; margin of ligula slightly rounded, ligula with 1 lig; premental sclerite feebly visible. Postmentum ( Fig. 191 ) with 3 pairs of pms, different in length.

THORAX AND ABDOMEN. Body length 1.3–1.8 mm (see Table. 1 ), elongate. Abdominal segments I–V almost of equal length, slightly larger than abdominal segments VI and VII ( Fig. 196 ). Spiracles on abdomen in median parts of segments (abdominal seg. I–VIII).

Chaetotaxy of body rather reduced. Setae moderately long or short and light yellow. Thorax. Prothorax ( Fig. 197 ) with 7 prn, 6 macro- and 1 microsetae; 2 moderately long ps of same length; 1 eus. Meso- and metathorax ( Fig. 197 ) with 1 prs; 2 pds, different in length; alar area with 1 short as; 1 short 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. 198 ) with 1 prs; 2 pds different in length; 1 ss; 1 eps; 1 ps; 1 lsts; and 2 short eus. Abdominal segment VIII ( Fig. 199 ) with 1 pds; 1 ss; 1 eps; 1 ps; 1 lsts; and 2 short eus. Abdominal segment IX ( Fig. 199 ) with 2 ds of different length; 1 ps; and 2 sts of different length. Anal lobes on abdominal segment X ( Fig. 199 ) with 1 very short, feebly visible seta.

Description of pupa. COLORATION. Body whitish yellow.

MORPHOLOGY ( Figs. 200–202 ). Body length 1.3–1.8 mm; widest part 0.7–0.9 mm (see Table. 1 ). Body rather stocky. Rostrum long, almost reaching metacoxae. Pronotum 1.8 times as wide as long.

CHAETOTAXY ( Figs. 200–202 ). Setae distinct, moderately long, or short, unequal in length, light yellow; on pronotum and head placed on conical protuberances. Head capsule including 1 vs, 2 os of different length, and 1 pas. Rostrum with 1 rs located medially. Vs and os 1 as long as setae on pronotum, distinctly longer than os 2, pas and rs. 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 2 setae. Each apex of femora without seta. Setae on abdominal segments I–VIII placed medially and laterally; all abdominal setae located on small, conical protuberance. Pseudocerci very short, in size as protuberances of other setae, slightly curved outside.

Biological observations. Pupae were found in the cells 9 days later the entrance of larvae into the soil. The duration of the pupal stage was 8 days. Adults emerged at the surface 2–3 days later.

Remarks. The same pods parasitized by T. pusillus were less intensively parasitized by Apion trifolii . In the same field also T. decretus was collected on Trifolium resupinatum . Tychius pusillus is known from central and southern Europe and northwestern Africa. It is noteworthy that in Sardinia the specimens of this species have the elytral integument almost completely reddish instead of black ( Caldara 1990).

Figures

FIGURES 190–195. Tychius pusillus mature larva head, antenna and mouth parts: 190—dorsal view (des—dorsal epicranial s., fs—frontal epicranial s., les—lateral epicranial s., ves—ventral epicranial s., st—stemmata, at—antenna); 191—right maxilla, dorsal view (dms—dorsal malar s., vms—ventral malar s., mpxs—maxillary palps s., pfs—palpiferal s., stps—stipital s.), prementum and postmentum, ventral view (prms—premental s., pms—postmental s., ligs—ligular s.); 192—right mandible (mds—mandible dorsal s.); 193—antenna; 194—labrum and clypeus (cls—clypeal s., lms—labral s.); 195—epipharynx (ams—anteromedial s., als—anteriolateral s., mes—median s., lr—labral rods).

FIGURES 196–199. Tychius pusillus mature larva habitus: 196—lateral view, 197—lateral view of thoracic segments, 198—lateral view of abdominal segment I., 199—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 200–202. Tychius pusillus pupa habitus: 200—ventral view, 201—dorsal view, 202—lateral view (vs—vertical s., os—orbital s., pas—postantennal s., rs—rostral s., as—apical s., ls—lateral s., ds—discal s., pls—posterolateral s., pc—pseudocerci).