Parallelodemas Faust

Prena, Jens & Zhang, Runzhi, 2014, A taxonomic revision of Parallelodemas Faust from South China (Coleoptera, Curculionidae, Baridinae), with notes on sexually dimorphic characters, Deutsche Entomologische Zeitschrift 61 (2), pp. 105-119 : 105-108

Genus Parallelodemas Faust

Parallelodemas Faust, 1894: 306. Type species Parallelodemas perfectum Faust, by subsequent designation ( Morimoto and Yoshihara 1996). Gender originally female, changed to neuter because of the grammatical gender of the Ancient Greek base word δέμας ( Alonso-Zarazaga and Lyal 1999).

Diagnosis.

Species of Parallelodemas can be recognized by characteristically elongate body (Fig. 1), medially notched epistome (which often is worn in females) and exodontous mandibles with evenly convex inner face (Fig. 3). Superficially, they resemble species of the conoderine subtribe Phaenomerina (see Morimoto 1961), but those have incrassate, ventrally dentate femora and larger eyes. The characters on the mandible and epistome separate Parallelodemas from certain grass- and sedge-associated, primarily Palaeotropical Baridinae with similarly slender rostrum and elongate body. The latter complex includes Eumycterus Schönherr, 1838; Trephognathus Marshall, 1945; Neosharpia Hoffmann, 1956; Caenobaris Nasreddinov, 1980; Lepidomyctides Yoshihara & Morimoto, 1994 and several species currently placed in other genera.

Misplaced species.

Yoshihara and Morimoto (1994) recognized that Parallelodemas tarsale Voss, 1937 is a species near Eumycterus and Lepidomyctides but they had very little material of those genera. We studied five Oriental species near Parallelodemas tarsale (BPBM, IZCAS, SNSD, ZIN) and several species of Caenobaris , Eumycterus , Neosharpia and Trephognathus Marshall from Africa, Central Asia and India. While Eumycterus and its probable synonym Trephognathus can be distinguished by vertically moving mandibles ( Marshall 1945; Korotyaev 2002), we were unable to recognize or to confirm the generic limits of the remaining species. We transfer here Parallelodemas tarsale to Lepidomyctides in the widest sense, as Lepidomyctides tarsalis (Voss), new combination.

Redescription.

Habitus: Total length 3.0-7.8 mm, width 0.8-2.2 mm; body slender subcylindrical (Fig. 1); integument black or brown, appendages and ventrites sometimes rufous; vestiture uniform or locally condensed to short vittae, setae either simple, squamiform, scalloped, deeply split or plumose. Head: Subspherical, contour often slightly warped at rostral base; eyes large, slightly encroaching on rostrum, bulging or flush with head contour, dorsally separated by width of rostrum at base; frontal fovea small to moderate; rostrum moderately elongate and slender, slightly curved, female with apical portion slightly inflated (Fig. 2); epistome produced and more or less notched, often worn off in females (Fig. 3); scrobe laterally descending, antenna inserted between midlength and apical fourth; funicle with 7 desmomeres; club compact, spindle-shaped, basal article approximately as long as remainder of club, not annexed to distal desmomere; mandibles with apparently abducent movement (away from center line and slightly ventrad), outer face with 1 large and 1-2 small secondary teeth, inner face convex and without teeth (Fig. 3). Prothorax: Barrel-shaped, elongate, nearly as wide as elytra. Anterior margin of pronotum not projected over frons, subapical constriction absent; basal margin bisinuous to accommodate projecting base of elytron; postoccular lobe feeble or absent. Prosternum without median channel, rarely slightly depressed in front of coxae; subapical constriction slight to moderate; basal lobe partially projected over mesosternum, with basal margin bifurcate or (rarely) truncate. Pterothorax: Mesoscutellum visible, trapezoid to subquadrate. Mesosternum unmodified. Mesepimeron smaller and narrower than mesepisternum, ascending between pronotum and elytron and visible in dorsal view. Metasternum medially depressed in male, flat or convex in female. Elytra: Elongate, sides subparallel, apices rounded individually, humerus developed, subapical callus feeble or absent, base at interstriae 3-6 slightly depressed and somewhat projected; striae 10, narrow but distinct, strial punctures not or slightly affecting edge of interstriae, strial setae absent; interstriae flat, punctate to transversely rugose, interstrial setae uniform or heterogeneous, modified setae restricted to basal and submedian vittae if present. Hindwings: Fully developed, length-width ratio 3.4-3.7, fore margin basally concave, anal lobe moderate, hind margin with setal fringe; venation agreeing with modal arrangement of subfamily ( Zherikhin and Gratshev 1995). Abdomen: Ventrites unmodified, not or indistinctly sexually dimorphic. Sclerolepidia small to medium-sized, densely packed, digitate. Stridulatory devices absent. Male genitalia and associated structures: Tergite VII without plectra for stridulation; tergite VIII shorter than wide, distally without transverse carina; sternite VIII laterally with sclerotized pyriform area, medially desclerotized; sternite IX variously strongly curved, distal prongs narrowly to widely diverging but always symmetrical; penis dorsoventrally depressed, longer than basal apodemes; internal sac extending approximately to midlength of apodemes when inverted, with sclerite at insertion of duct or with pigmented flagellum; tegmen with ring dorsally closed, basal apodeme obsolete, parameroidal lobes developed. Female genitalia and associated structures: Tergite VII longer than wide, without transverse carina, setal vestiture squamiform basally and piliform distally, plectra for stridulation absent; sternite VIII distally forked into weakly sclerotized, widely dilated, U-shaped arms; hemisternite pigmented, stylus 1.9 –2.2× as long as wide, distal setae half as long as stylus; bursa pouch-like, half as long as vagina; spermatheca sclerotized, collum short, often somewhat bulbous, ramus inserted on outer face of collum (facing away from cornu), rudimentary to long; spermathecal duct unpigmented, at most slightly longer than spermatheca, inserted distally in bursa. Legs: Procoxae separated by less than 1/3 diameter of coxa; pro- and mesofemora clavate, hindfemur less expanded and often partially sulcate ventrally; tibiae straight to curved (depending on ventral profile of femur), ventrodistal spine spiniform, robust and large on pro- and mesotibiae but somewhat smaller on metatibia; tarsus with 5 segments, third with anterior margin faintly to deeply excised, fifth long to greatly reduced, claws flat and basally fused, or miniaturized and medially fused to single blade.

Diversity and distribution.

With the six new species described in this study, Parallelodemas includes now a total of twelve. The scarce material gives an unrepresentative picture of the distributional ranges of individual species. Species of Parallelodemas have been found in China, India, Laos, Malaysia, Myanmar, Taiwan and Vietnam. Their distribution is primarily Oriental but several reach the Palaeartic part of China, northward up to Shaanxi and Zhejiang.

Biology.

The host plant of Parallelodemas apparently is unknown. One specimen of Parallelodemas docile is labeled as being taken from Buttontree, Anogeissus acuminata (Roxburgh ex Candolle) Guillemin et al. ( Combretaceae ). Other specimens were swept from low vegetation. Females with fully developed eggs occur from late April to early June.

Sexual dimorphism.

Rostrum. Species of Parallelodemas exhibit marked sexual dimorphism of characters on the rostrum. Females generally have a longer and smoother rostrum than males, with a more basally inserted antenna and slightly inflated apical portion (Fig. 2). Gender-related differences in the basal width of the rostrum (Fig. 8) are apparent but often inconspicuous. The ventral side of the rostrum is setose in male Parallelodemas impar , Parallelodemas petilum and Parallelodemas plumosum . However, the most striking difference, the length and shape of the epistome, may be acquired secondarily rather than being truly sexually dimorphic. Nearly all examined males have a projected, medially notched epistome, whereas it is almost always short and truncate in females (Fig. 3). However, the presence of projected epistomes in some female Parallelodemas feae , Parallelodemas impar , Parallelodemas imperfectum and Parallelodemas setifrons suggests a secondary loss, probably through abrasion during the preparation of oviposition sites, because the distally divergent mandibles afford no protection of the epistome as in other weevils. However, this needs to be confirmed with freshly emerged specimens and field observations.

Antenna. Males generally have a longer scape than females (usually as long as the funicle). The distal margins of the male scape can be setose, such as in Parallelodemas impar (Fig. 2).

Mandible. At a first glance, it appears as if Parallelodemas has swapped the left with the right mandible or rotated them by 180 degrees (Fig. 3). The inner face not only lacks any trace of incisors, it also is evenly convex from base to apex and seems therefore dysfunctional. Moreover, the outer face is concave and armed with two apparently ordinary incisors, just like the inner mandibular face of most baridine weevils. However, three landmarks on the mandible leave no doubt that the seemingly abducent mandibular movement evolved by reversing the function of the abductor and adductor tendons rather than by rotating the mandible, a trend seen in some weevils with a very slender rostrum ( Marshall 1945): (1) The dorsal and ventral mandibular sockets (preartis and postartis) are formed and located as in other Baridinae; (2) the mandibular setae are located on the outer face (between the basal incisors); and (3) the pharyngeal process is attached to the inner basal angle of the mandible. From this it follows that the incisors on the outer face are secondarily evolved structures and analogous to the inner incisors of other weevils. Morimoto and Yoshihara (1996) suggested an inversion of the mandibular movement from adducent to abducent. The laterally deeply excised mandibular articulation and widely divergent mandibles in many mounted specimens support this conclusion. Unfortunately, we could obtain neither direct field observations nor fresh specimens for scanning the abductor and adductor tendons.

Eye. While almost all Baridinae have eyes that are flush with the head contour, they are protruded in several Parallelodemas species. The eyes of male Parallelodemas setifrons protrude more than those of females (Fig. 8), but the dorsal and ventral distance between them and their circumference are not affected. The increased eye surface affords more facets in the male but facet diameter is the same.

Leg. Several Parallelodemas species have large, deviant setae on the mesotarsus which crowd toward the distal (outer) half. These setae are arranged asymmetrically on the fifth (claw-bearing) tarsite and are much larger and more numerous in males than in females (Figs 6, 7). The individual tarsites, in particular the fifth, are often more elongate in males than in females. Males often have faintly thicker pro- and mesofemora than females.

Tergites. Like in other Baridinae, the eighth tergite is developed in males but internalized in females. Because the distal external tergite protrudes beyond the elytral apex well enough to expose the suture between the seventh and eighth tergites in males, this character is very useful for sexing specimens.

Ventrites. The male metaventrite is medially depressed and, together with the first abdominal ventrite, may have less setae than the female’s. Voss (1941) mentioned a sexually dimorphic basal process on the prosternum of Parallelodemas impar , but he either had a mixed series or his observation was incorrect.

Key to the species of Parallelodemas found in China