Microchilus Blanchard, 1851

Jameson, Mary Liz, 2008, Review of the genus Microchilus Blanchard (Coleoptera: Scarabaeidae: Rutelinae: Geniatini), Insecta Mundi 2008 (25), pp. 1-14 : 6-9

Genus Microchilus Blanchard, 1851

( Fig. 1-4 , 8 -25)

Microchilus Blanchard 1851: 240 . Type species Microchilus lineatus Blanchard, 1851 (by monotypy).

Description. Scarabaeidae , Rutelinae , Geniatini . FORM ( Figs. 1-4 ): Body elongate oval, sides subparallel, dorsum convex, pygidium exposed, elytral apex broadly rounded. Surface shagreened. HEAD: Surface punctate. Frons weakly convex (not weakly concave as in Xenogeniates ). Frontoclypeal suture complete, straight. Eye canthus simple, not carinate. Clypeus with apex reflexed, lacking bead. Mandible (e.g., Fig. 12 ) with baso-external edge rounded, apical margin rounded, inner apex with 1 tooth; inner teeth lacking; molar region poorly or well defined. Labrum (e.g., Fig. 8 ) apicomedially with forward-projecting, acute tooth. Maxilla (e.g., Fig. 10 ) with baso-external edge of mala round, inner apex with 2-4 ridges; stipes with margins subparallel. Mentum (e.g., Fig. 9 ) in ventral view subhexagonal; disc greatly convex. Apex with well developed median, dorsally-produced tooth. Antenna 9-segmented with 3-segmented club, some fusion of segments 2-7 (stem); club elongate-oval in lateral view; sexual dimorphism apparent in club length (club of male longer than club of female). PRONOTUM: Widest at middle; anterior angles rounded. In frontal view, dorsal surface weakly convex. Surface variably punctate. Marginal bead incomplete at apex and base. SCUTELLUM: Parabolic, apex weakly acute, width about 1.5 times longer than length in the middle; surface variably punctate. ELYTRON: Surface with variably defined punctures and striae. Elytral suture length subequal to width of both elytra. Margins beaded; bead obscured at apex. Elytral apex weakly rounded. Epipleuron rounded in cross section; ventral side bare, lacking setose ridge or hairs, membrane present from metacoxa to apex. PYGIDIUM: Shape broadly triangular. Surface variably sculptured. Margin with sides and apex beaded. VENTER: Prosternal shield present, ventrally produced, hidden between procoxae. Mesometasternal keel lacking. Mesosternum not invaginated or forming a pit. In lateral view, male abdominal sternites flat or weakly convex, female abdominal sternites weakly or strongly convex. Terminal sternite in male with apex weakly emarginate, not emarginate in female. LEGS (e.g., Fig. 11 , 15-20 ): Protibia with 2 teeth, weak swelling occasionally present in location of third tooth; inner apex with spur (not ventrally curved); base without notch. Protarsomere I variable in length (subequal to 3 times longer than protarsomere 2). Protarsomeres II-IV dorsoventrally flattened (less so in female), moderately densely or densely setose ventrally; setae short, tawny. Protarsomere V weakly flattened, with sparse ventral pilosity, inner apex with broad longitudinal slit. Protarsus with inner and outer claws unequally incised dorsoventrally ( Fig. 11 ); unguitractor plate laterally flattened, weakly exposed beyond apex of protarsomere V, bisetose. Meso- and metatibia each expanded apically (mesotibial apex slightly more expanded in females); external edge with or without 1-2 weakly developed carinae; apex with spurs and spines; outer spur (male and female) half length or less than half length of inner spur; inner apex placed in depression. Surface variably punctate. Male meso- and metatarsomere I ventrally flattened or cylindrical, tarsomeres II-IV flattened, tarsomere V cylindrical with weakly developed sub-basal tooth, setose ventrally or not (tarsomeres I and V less setose), setae short, tawny; mesotarsus with inner and outer claws unequally incised dorso-ventrally; inner apex with weak longitudinal slit. Female meso- and metatarsomeres I-V subconical or weakly flattened ventrally, setose ventrally or not, setae short, tawny; metatarsomere V with weakly developed sub-basal tooth; mesotarsus with inner and outer claws unequally incised dorsoventrally; inner apex with weak longitudinal slit. Metafemur with dorsal, apicolateral area smooth, lacking stridulatory file. HIND WING ( Fig. 14 ): Sparse, weakly developed hooks on precostal membrane present. Anterior edge from medial fold to apex of wing lacking setae. Vein AA 1+2 about 1/3 length of vein AA 3+4. PARAMERES ( Fig. 21-24 ): Shape symmetrical, diagnostic at the species level. FEMALE GONOCOXITES ( Fig. 13 ): Shape symmetrical, not diagnostic at the species level.

Diagnosis. Within the Geniatini , members of Microchilus are diagnosed by the following characters: both claws on all legs (males and females) incised (shared only with members of the Bolax campicola group); protibia with two external teeth; protarsomeres dorsoventrally flattened, fifth protarsomere weakly flattened (most geniatines have some tarsomeres dorsoventrally flattened, but flattening of the fifth protarsomere is not commonly observed), and small size (less than 8.1 mm in length).

Distribution (Fig. 25). Central to eastern and southeastern Brazil.

Natural History. Ohaus (1908) reported that M. lineatus feeds on Aristida pallens Cav. (Poaceae) . Ohaus (1900) reported that M. lineatus is diurnal and can be found on vegetation.

Remarks. Microchilus is unusual among the Rutelinae based on its small size (less than 8.1 mm), both claws on all legs incised in males and females, fifth protarsomere weakly flattened, and protibia with two external teeth. These characters serve to diagnose the genus.

Among the Geniatini , the genus differs from members of the genus Eunanus due to form of the claws (all claws simple in Eunanus ; all claws incised in Microchilus ) and form of the mandibular apex (with a rounded, apical tooth in Eunanus ; lacking rounded, apical tooth in Microchilus ).

The genus differs from members of the genus Leucothyreus due to the form of the claws (one claw simple and one claw incised on all legs in Leucothyreus ; all claws incised in Microchilus ) and surface of pygidium (with well defined horizontal striae in Leucothyreus ; with punctures or poorly defined horizontal striae in Microchilus ).

The genus differs from members of the genus Bolax due to the form of the labrum (apex with a broad tooth in Bolax ; apex with a narrow tooth in Microchilus ), length of antennal club in the male (1.5 times length of segments 2-7 in Microchilus ; subequal to segments 2-7 in Bolax ), form of the protibial teeth (two external teeth in Microchilus ; three external teeth in Bolax ), and form of the pronotum (lacking longitudinal constrictions in Microchilus ; often with longitudinal constrictions at apex and base in Bolax ). Microchilus species share a few characters with members of the Bolax campicola group ( B. campicola Machatschke , B. flavolineata [Mannerheim], and B. saucia Ohaus ). Species in the Bolax campicola group and members of Microchilus share the unusual incised internal and external claws on all legs. Whether the character of the claws is convergent or synapomorphic in Microchilus and Bolax will require phylogenetic analyses. Based on the characters that separate the genera Bolax and Microchilus , I treat Microchilus as a valid, monophyletic genus.

Other genera of Geniatini that are easily distinguished from Microchilus . See “Taxonomic History”, “Status of Microchilus beckeri ”, and “Diagnosis” for additional discussion of the genus.

Figures

Figure 1-7. Habitus images Microchilus species and other Geniatini. 1) Microchilus lineatus, male. 2) M. lineatus, female. 3) M. rodmani, holotype male. 4) M. rodmani, allotype female. 5) Bolax foveolata Blanchard, male. 6) Leucothyreus beckeri, male. 7) Eunanus murinus Ohaus, male. Scale line = 1.0 mm.

Figure 8-14. Generic characters for members of the genus Microchilus. 8) Labrum and clypeus, frontal view of M. lineatus. 9) Mentum, ventral view of M. lineatus. 10) Right maxilla, ventral view of M. lineatus. 11) Claws, dorsal oblique view of M. lineatus. 12) Left mandible, dorsal oblique view of M. lineatus. 13) Gonocoxites, dorsal view of M. lineatus. 14) Left wing, ventral view of M. rodmani. Scale line = 0.5 mm.

Figure 15-24. Diagnostic characters of Microchilus species. 15) Right protarsomeres of male M. lineatus, dorsal view. 16) Right protarsomeres of male M. rodmani, dorsal view. 17) Right metatibia of M. lineatus, ventral view. 18) Right metatibia of M. rodmani, ventral view. 19) Right protarsomeres of female M. lineatus, ventral view. 20) Right protarsomeres of female M. rodmani, ventral view. 21-22) Parameres of M. lineatus, dorsal view and lateral view, respectively. 23-24) Parameres of M. rodmani, dorsal view and lateral view, respectively. Scale line = 0.5 mm.