Lankaphthona Medvedev, 2001

Ruan, Yongying, Konstantinov, Alexander S., Prathapan, Kaniyarikkal D., Zhang, Mengna & Yang, Xingke, 2019, A review of the genus Lankaphthona Medvedev, 2001, with comments on the modified phallobase and the unique abdominal appendage of L. binotata (Baly) (Coleoptera, Chrysomelidae, Galerucinae, Alticini), ZooKeys 857, pp. 29-58 : 29

Genus Lankaphthona Medvedev, 2001

Lankaphthona Medvedev, 2001: 162-163. Type species: Lankaphthona micheli Medvedev, by original designation.

Philotarsa Medvedev, 2009:147. Type species: Philotarsa laosica Medvedev, 2009:147, by original designation. New Synonym.

Longitarsella Medvedev, 2009: 202 (originally as a subgenus of Trachyaphthona ). Type species: Philotarsa laosica Medvedev misidentified as Lankaphthona binotata (Baly, 1876) (originally as Thyamis binotata Baly, 1876), by original designation. New Synonym.

Distribution.

China, Vietnam, Thailand, India, Sri Lanka .

Statistics.

8 species.

Host plants.

Adults of L. nigronotatus , (Jacoby, 1896) feed on the leaves of Menispermaceae . This is the first report of the host plants of the genus.

Diagnosis.

The relationships between the flea beetle genera with subparallel ridges on the first abdominal ventrite are in need of comprehensive reevaluation with a rigorous morphological and molecular phylogenetic study. Lankaphthona closely resembles Tegyrius and Parategyrius based on preliminary external morphological characters. These three genera share an overall body shape, long first metatarsomere and similar structure of the head. Tegyrius can be separated from Lankaphthona by a very narrow orbit (orbit is generally wider in Lankaphthona ), anteromesal ends of antennal calli acutely narrowed and slightly entering into the interantennal space (in Lankaphthona anteromesal ends of antennal calli reach interantennal space, however, does not enter as deep as in the type species of Tegyrius , T. metallicus Jacoby. This character is difficult to use consistently to separate all known species of Lankaphthona and Tegyrius ); deep sulci delimiting antennal calli (sulci delimiting antennal calli are shallow in Lankaphthona ); and four labral setae (number of labral setae vary in Lankaphthona from 4 to 14). Lanka can be distinguished from Lankaphthona by the depressed antennal calli separated from each other by the frontal ridge (antennal calli are neither depressed nor separated from each other by the frontal ridge in Lankaphthona ). In Philogeus , antennal calli are separated from each other by the frontal ridge and the bifid claws (in Lankaphthona , the antennal calli are not separated completely from each other, and the claws are appendiculate). In Neorthana , the frontal ridge is almost rectangular in frontal view and forms an abrupt angle with anterofrontal ridge in lateral view (frontal ridge forms a triangular ridge with anterofrontal ridge and never forms an abrupt angle with anterofrontal ridge in lateral view in Lankaphthona ). In Bikasha , the frontal ridge is narrowed anteriorly above the anterofrontal ridge, the elytral punctures are regularly arranged and the first metatarsomere is shorter (frontal ridge is broadened anteriorly forming a triangular ridge with anterofrontal ridge, elytral punctures confused and the first metatarsomere is longer in Lankaphthona ). Type material of Parategyrius was not available for our study, but specimens identified as congeneric, examined by us, resemble Lankaphthona and hence the former is likely to be a senior synonym of Lankaphthona .

Lankaphthona can be easily separated from Trachytetra by the following characters: 1) first metatarsomere almost as long as, or longer than, half of metatibia (first metatarsomere much shorter than half of metatibia in Trachytetra ); 2) longitudinal subparallel ridges present on first abdominal ventrite (absent in Trachytetra ); 3) antennal calli moderately developed, indistinctly enter into the interantennal space (antennal calli strongly developed, distinctly enter into the interantennal space in Trachytetra ). Characters separating Lankaphthona and Lankanella are a few: frontal and anterofrontal ridges merging into each other forming more or less well-defined Y-shaped structure and confused elytral punctures in Lankaphthona and arranged in regular rows in Lankanella . In Lankanella , frontal and anterofrontal ridges more clearly separated from each other forming more or less well-defined T-shaped structure and the elytral punctures are regularly arranged.

Lankaphthona superficially resembles Aphthona Chevrolat in having similar characters of head and body shape. However, Lankaphthona can be easily differentiated from Aphthona by the longer first metatarsomere, presence of antebasal transverse impression on pronotum and the subparallel ridges on first abdominal ventrite. Lankaphthona can be confused with Longitarsus Latreille due to the general body shape and the elongate first metatarsomere, and there are also several species of Longitarsus having black maculation on elytra (e.g. Longitarsus transversalis Chen, 1935 from Northern India, Longitarsus bimaculatus (Baly, 1874) from China and Japan). However, Lankaphthona can be separated from Longitarsus by the shape of the frontal ridge and antennal calli, the presence of the antebasal transverse impression on the pronotum and paired intercoxal subparallel ridges on the first abdominal ventrite (both the antebasal transverse impression on the pronotum and the subparallel intercoxal ridges or the appendage on first abdominal ventrite are absent in Longitarsus ).

Among other Oriental genera, Doeberlnotus Prathapan, Konstantinov & Ruan, 2017 and Sanckia Duvivier, 1891 have elongate first metatarsomere. Lankaphthona can be differentiated from Doeberlnotus by the smooth pronotum and body color without metallic luster (pronotum bumpy and body color metallic in Doeberlnotus ); from Sanckia by the glabrous body surface, presence of antebasal groove on pronotum and confused elytral punctation (in Sanckia , body surface is covered with dense hair, antebasal transverse impression of pronotum is absent and the elytral punctures are arranged in regular lines.

Description.

Small, oblong to oval, convex in lateral view; length 1.5-2.4 mm; 1.6-1.9 times longer than wide, width 0.8-1.3 mm. Color non-metallic, straw brown to red-brown to black.

Head hypognathous. In lateral view, vertex and antennal calli as well as frontal ridge separately form convex lines, meeting point of frontal ridge and antennal calli concave in lateral view. In frontal view, vertex moderately convex, minutely punctate, with obtusely angulate anterior margin. Supraorbital pore situated adjacent to orbital sulcus, with adjacent minute setiferous pores. Antennal callus transverse to oblique, 1-2 times wider than long, separated from vertex. Antennal callus as high as vertex or lower; often a little lower near supracallinal sulcus, much lower near antennal socket than near supracallinal sulcus. Supracallinal sulci distinct, not deep, shallower than orbital sulcus. Anteromesal ends of antennal calli not distinctly angulate, reach up to or slightly entering into interantennal space; antennal calli separated by dorsal end of frontal ridge or narrowly to broadly connected to each other. Supracallinal sulcus transverse to oblique, mostly convex, rarely concave. Midcranial suture absent. Orbit well differentiated from antennal callus by supraorbital sulcus. Subgenal suture well developed along base of mandible. Eye anterolateral, inner margin weakly concave near antennal socket, gently diverging ventrad, vertical diameter 1.2-1.4 times transverse diameter. Distance between eyes 3.0-4.0 times diameter of a socket, 0.9-1.4 times transverse diameter of one eye. Diameter of antennal socket 2.3-4.5 times distance between eye and adjacent socket. Distance between antennal sockets 0.8-1.0 times diameter of a socket. Frontal ridge and anterofrontal ridge together form a triangular ridge, flat anteriorly. Frontoclypeal suture with a row of setae. Antenna filiform, reaching beyond middle of elytra or longer. First and second antennomeres thick, next four or five thin, distal ones slightly thickened. First antennomere longer than second or third separately, little shorter than second and third combined. Labrum with 4-14 setiferous pores arranged irregularly or regularly in transverse row. Maxilla with apical plapomere pointed, shorter or longer than penultimate palpomere. Penultimate palpomere distinctly widened.

Pronotum 1.1-1.6 times wider than long. Antebasal transverse impression sinuate in middle, merge with posterior margin laterally. Almost absent in Lankaphthona micheli Medvedev, however, traces of antebasal transverse impression evident laterally. Width of pronotum anteriorly subequal to width posteriorly. Lateral margin evenly and gently curved. Anterolateral callosity about two times longer than wide, convex and oblique in dorsal view, forms obtuse denticle at pore, pore situated at posterodorsal face of callosity. Posterolateral callosity slightly or strongly protruding, with pore situated laterally. Posterior margin weakly, but distinctly bisinuate, forming lobe in middle. Pronotal punctures minute to small, apparently greater than those on vertex. Anterior coxal cavities open behind. Intercoxal prosternal process extending beyond coxa, apical margin convex, convexly raised along top; apex widened, often with preapical depressions. Shortest width of intercoxal prosternal process more than shortest distance between anterior margin of prosternum and coxal cavity. Prosternum 1.5-1.6 times as long as mesosternum, 0.6 times as long as metasternum. Distance between anterior margin of prosternum to end of prosternal intercoxal process 2.8-6.3 times width of prosternal intercoxal process; width of prosternal intercoxal process 1.2-2.7 times minimum distance between anterior margin of mesosternum to coxal cavity.

Elytra basally wider than pronotum, with basal callus not distinct, without depression posteriorly; humeral callus with or without depression mesally. Elytral punctures confused, fine yet stronger than those on pronotum. Elytral epipleuron extending beyond 3/4 of elytron, hardly reaching apex, subhorizontal to outwardly oblique with maximum width subequal to that of midfemur. Hind wings fully developed. Visible part of mesoscutellum flat, triangular with broadly rounded apex. Mesosternal intercoxal process depressed anteriorly, raised in posterior half. Distance between anterior margin of mesosternum to end of intercoxal mesosternal process 0.8-1.2 times width of mesosternal intercoxal process; width of mesosternal intercoxal process 2.6-4.0 times minimum distance between anterior margin of mesosternum to coxal cavity. Metasternum with anterior margin strongly convexly arched, convexly raised posteriorly, forming paired protuberances raised much above level of metacoxa, as is typical in other genera of the group.

Pro- and mesotibiae dorsally convex, without apical spine. Metafemur robust with anterior margin strongly convex, posterior margin weakly convex. Metatibia in dorsal view distinctly, but weakly curved, with apex directed outwardly. Metatibia almost straight or weakly curved in lateral view; in dorsal view gradually widening from proximal end till it narrows preapically; dorsally convex proximally, turning flat beyond proximal 1/3; distinctly margined both mesally and laterally. Lateral margin with row of pointed bristles, absent proximally up to 2/3 length or less. Mesal margin apically with row of pointed bristles, row of bristles being much shorter than that on lateral margin. Spinules absent on both lateral and mesal margins. Metatibial spine positioned at middle of apex, pointed, shorter than width of metatibial apex. Tarsal articulation on metatibia visible in lateral view, on callosity flanked by flat sclerite on either side. First metatarsomere as long as or longer than half of metatibia, subequal to or longer than next three combined, ventral side densely covered with dense capitate setae. Second metatarsomere apparently longer than third. Third metatarsomere deeply bilobed. Claw appendiculate, apparently shorter than metabitial spine.

Intercoxal part of first abdominal ventrite raised, subparallel ridges on first abdominal ventrite weakly to well developed. Apical tergite of female without longitudinal groove along middle.

Spermatheca with distinct pump, receptacle and duct. Duct not coiled. Receptacle cylindrical, longer than wide, longer than pump.

Sexual dimorphism.

In Lankaphthona , males can be differentiated from females by the apex of the last abdominal ventrite tri-lobed and incised (evenly convex in female). In L. nigronotata (see Fig. 8H) and L. micheli , males have much longer antennae than females. A spoon like appendage arising from the first abdominal ventrite in males of L. binotata (Fig. 3 B–E), is absent in females.

One of the most common characters to separate males and females in flea beetles is the enlarged first protarsomere in males. However, the first protarsomere is not sexually dimorphic in Lankaphthona , as males and females have more or less the same sized first protarsomere.

Variation.

The maculation on elytra is highly variable in most species of Lankaphthona . It could be indistinct or entirely absent in some cases. The color of maculation varies from brown to black in different individuals of the same species. The body color also varies from pale yellow to light brown in some species.

Remarks.

Trachyaphthona Heikertinger, 1924 was synonymized with Trachytetra Sharp, 1886 by Konstantinov and Prathapan (2008: 413). However, Medvedev (2009) treated Trachyaphthona as a valid genus name without justification. Here we consider it as a junior synonym of Trachytetra .

In most flea beetle genera, the number of labral setae is usually conservative and considered as a more or less reliable generic character. In most cases, there are four (e.g., Lanka , Tegyrius ) or six (e.g., Chaetocnema Stephens, Bikasha ) labral setae. However, the number of labral setae varies greatly in Lankaphthona . For instance, there are seven pairs of setae in Lankaphthona nironotata , five pairs in L. micheli and two pairs in L. yunnantarsella sp. nov.