Tychius (s. str.) breviusculus 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 : 19-20

Tychius (s. str.) breviusculus Desbrochers, 1873

Caldara 1990: 182.

Material examined. 12 larvae from pods of Melilotus alba Medicus collected 30.vii.1982 at Rozzano , Milano province, Lombardia (northern Italy), leg. R. Caldara, and 11 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 to dark brown. All thoracic and abdominal segments salmon.

HEAD CAPSULE AND MOUTH PARTS. Head width: 0.40–0.42 mm (see Table. 1 ). Endocarinal line present, relatively short. Des 1 located almost in central parts of epicarnium; des 2, des 3 and des 4 located along frontal suture; des 5 located anterolaterally; des 4 4 times shorter than des 3 and des 5 ( Fig. 138 ). Fs 1 and fs 2 absent; fs 3 short, located medially; fs 4 located anteromedially (along epistoma); fs 5 located anterolaterally (along epistoma), both 3 to 4 times longer than fs 3 ( Fig. 138 ). Les almost as long as des 3. Ves 1–2 very short. Post-epicranial area with group of 3 minute pes. Antennal segment membranous, bearing conical sensorium and 3 very short, triangular, sensilla ( Fig. 141 ).

Labrum ( Fig. 142 ) approximately 3 times as wide as long; lms 1 slightly shorter than lms 2 and lms 3; anterior margin almost straight. Clypeus ( Fig. 142 ) 2.8 times as wide as long; with 2 pairs of very short cls of same length, and 1 sensillum, all posterolaterally; anterior margin slightly sinuate. Epipharynx ( Fig. 143 ) with 2 pairs of als, different in length; with 2 pairs of short and triangular ams; with 3 long finger-like mes; labral rods short, kidneyshaped, slightly converging posteriorly. Mandibles ( Fig. 140 ) with 2 short mds. Maxilla ( Fig. 139 ): stipes with 1 stps, and 2 pfs of equal length; 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 almost 1:1; basal palpomera with 1 short mpxs; distal palpomera with group of 3–4 conical, cuticular apical processes. Prementum ( Fig. 139 ) almost rounded, with 1 prms; margin of ligula slightly curved outside; ligula with 2 lig; premental sclerite distinct. Postmentum ( Fig. 139 ) with 3 pairs of pms, different in length.

THORAX AND ABDOMEN. Body length 1.8–2.5 mm (see Table 1 ), moderately elongate. Abdominal segments I–VI almost of equal length ( Fig. 144 ). Spiracles on abdomen in anteromedian parts of segments (abdominal seg. I–VIII).

Chaetotaxy of body rather reduced. Setae moderately long or short and light yellow. Thorax. Prothorax ( Fig. 145 ) with 8 prn, 6 macro- and 2 microsetae; 2 moderately long ps of same length; 1 eus. Meso- and metathorax ( Fig. 145 ) with 1 prs; 2 pds, different in length; 1 very short ss; 1 eps; 1 ps; and 1 eus. Each pedal area of thoracic segments well-separated and with 2 pda. Abdomen. Abdominal segments I–VII ( Fig. 146 ) with 1 prs; 2 pds different in length; 1 very short ss; 1 eps; 1 ps; 1 lsts; and 1 short eus. Abdominal segment VIII ( Fig. 147 ) with 1 pds; 1 ps; 1 lsts; and 2 short eus. Abdominal segment IX ( Fig. 147 ) with 1 ds; and 1 sts. Anal lobes on abdominal segment X ( Fig. 147 ) with 1 very short, feebly visible seta.

Description of pupa. COLORATION. Body salmon.

MORPHOLOGY ( Figs. 148–150 ). Body length 2.0– 2.4 mm; widest part 0.6–1.0 mm (see Table. 1 ). Body elongate, slender. Rostrum moderately long, approximately 3 times as long as wide, not reaching mesocoxae. Pronotum 1.5 times as wide as long.

CHAETOTAXY ( Figs. 148–150 ). Setae slightly distinct, short, unequal in length, light yellow; on pronotum and head placed on small protuberances. Head capsule including 1 vs, 1 os, and 1 pas. Rostrum without setae. Setae on head slightly shorter than setae on thoracic and abdominal segments. Pronotum with 2 as, 2 ls, 2 ds, and 1 pls; ds as long as 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 posteromedially and posterolaterally; all abdominal setae located on small, conical protuberances. Pseudocerci very short, slightly curved outside.

Biological observations. Pupation 8 days after the entrance of larvae into the soil. Duration of the pupal stadium was 6 days. Adults quickly emerged at the surface 2–3 days later. At the moment of the collection of the mature pods, adults were very common and several of them were in copula. In the same plant also many adults of T. meliloti were collected. 20% pods collected were infested by larvae of Tychius . This number apparently small is instead relevant since, as is well known, the number of pods in a single plant of M. alba is very high. Fortunately the living larvae of the two species are easy to distinguish since those of T. meliloti have the forehalf of the body lemon yellow in colour and the head dark brown, whereas in T. breviusculus the body is completely white and the head lighter (these differences are poorly evident in larvae preserved in alcohol). Therefore it was possible to put larvae of the two species in different container for the pupation and to establish that in our sample the larvae of T. meliloti were more numerous (15 % vs 5 %). The fact that two closely related species parasitize the same plant in the same period and apparently in the same manner is surely interesting. A careful search of galls in the flowers and on the leaves was unsuccessful.

Remarks. It was already reported that more than one species of Tychius may occur in the same plant ( Caldara 1986, 1990). In the two better studied cases, T. crassirostris Kirsch, 1871 and T. meliloti on Melilotus alba in Germany ( Mik 1885; Urban 1935), and T. medicaginis C. Brisout de Barneville, 1863 and T. aureolus Kiesenwetter, 1852 on Medicago sativa L. in France (D'Agular & Perrier 1974), it was observed that T. crassirostris and T. aureolus developed in galls and the others in pods. Sometimes T. meliloti coexists with T. breviusculus on M. alba in northern Italy, whereas the former coexists with T. bicolor C. Brisout de Barneville, 1863 in central and southern Italy (R. Caldara, pers. observ.).

However, two years after the first observation, another collection of pods was made from M. alba in the same locality and in the same period. It is noteworthy that adults of T. breviusculus were distinctly more numerous than adults of T. meliloti at a rate of 10:1 and the same rate was observed in the collection of larvae.

Figures

FIGURES 138–143. Tychius breviusculus mature larva head, antenna and mouth parts: 138—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); 139—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.); 140—right mandible (mds—mandible dorsal s.); 141—antenna; 142—labrum and clypeus (cls—clypeal s., lms—labral s.); 143—epipharynx (ams—anteromedial s., als—anteriolateral s., mes—median s., lr—labral rods).

FIGURES 144–147. Tychius breviusculus mature larva habitus: 144—lateral view, 145—lateral view of thoracic segments, 146—lateral view of abdominal segment I., 147—lateral view of abdominal segments VIII–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 148–150. Tychius breviusculus pupa habitus: 148—ventral view, 149—dorsal view, 150—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).