Quadriops Hansen, 1999

Giron, Jennifer C. & Short, Andrew Edward Z., 2017, Revision of the Neotropical water scavenger beetle genus Quadriops Hansen, 1999 (Coleoptera, Hydrophilidae, Acidocerinae), ZooKeys 705, pp. 115-141 : 116-118

Quadriops Hansen, 1999

Quadriops Hansen, 1999: 131.

Type species.

Quadriops depressus Hansen, 1999 by original designation.

Differential diagnosis.

Small to very small beetles, total body length 1.6-2.6 mm, width 1.1-1.6 mm. Color yellowish to reddish to dark brown. Body shape oval in dorsal view; subhemispherical and sometimes dorsally flattened in lateral view (see Figs 1-3). Frons lateral and posteriorly expanded, forming a canthus that completely divides the eyes in dorsal and ventral portions (e.g. Fig. 1B, 3B). Antennae with nine antennomeres (e.g. Fig. 2C). Maxillary palps curved inward, rather short and stout (e.g. Figs 1C, 2G). Elytra with punctures either irregularly distributed (Fig. 1) or forming ten well defined longitudinal rows, with additional elytral ground punctures along interstriae (Figs 2, 3); elytra without sutural striae, narrowly explanate anteriorly, explanation gradually broader towards apex (see Figs 1-3). Posterior elevation of mesoventrite, usually with a well-defined transverse ridge (except in Q. dentatus which possesses an acute tooth). Posterior femora glabrous with the exception of a few very scattered small setae. Fifth abdominal ventrite apically rounded and without stout setae (e.g. Fig. 1C).

Description.

Body broadly oval, weakly convex, with dorsum distinctly flattened in some species. Head. Eyes completely divided into dorsal and ventral faces by lateral canthus of the frons; dorsal face of eye tear-drop shaped, smaller in size relative to the ventral face. Antennae (see Fig. 4A) with 9 antennomeres, usually paler than general coloration of head; antennomere 1 reaching midpoint of ventral face of eye (reaching cardo-stipes joint), nearly 1.5-times longer than antennomere 2; antennomere 3 nearly as long as antennomeres 4-5 combined; antennomere 6 forming a rather small, but well differentiated cupule, antennomeres 7-9 similar in size, slightly flattened, forming a loosely articulated, pubescent club; setae at apex of antennomere 9 longer than general pubescence of club. Temporae forming a rather flat surface behind the eyes, densely covered by setae (hydrofuge pubescence, see Fig. 4B). Frons and clypeus (see Fig. 4A, C) with ground punctures uniformly distributed over the surface, accompanied by scattered seta-bearing systematic punctures; setae particularly noticeable on frons anterior to the eye, including lateral canthus, and behind frontoclypeal suture; surface between punctures ranging from smooth to finely reticulated, especially on anterior region of clypeus; anterior corners of clypeus widely rounded; anterior margin of clypeus usually emarginate medially, with distinct bead along entire margin. Labrum reduced, paler, rather short and wide, sometimes appearing deflexed and concealed by clypeus from above (see Fig. 4C); dorsal surface convex and finely reticulated; anterior margin mesally widely emarginate and bent inwards; lateral margins bearing a row of long setae. Maxilla (see Fig. 4A) usually with sparse setae on ventral surface of cardo and stipes, with a row of stiff decumbent spiniform setae along outer dorsal margin of palpifer; maxillary palps yellowish, shorter than antennae, and somewhat stout; palpomeres similar in size; palpomere 1 shorter than stipes, with inner margin straight, and outer margin distally strongly convex; palpomere 2 conical (narrower at base), with inner margin convex at base and outer margin widely convex; palpomere 3 digitiform, rather elongate (compared to 1 and 2), apically somewhat truncate; apex of palpomere 3 bearing sensilla. Mandibles with apex bifid (examined in Q. clusia and Q. reticulatus ). Labial palps yellowish, nearly as long as mentum, dorsoventrally flattened; palpomere 2 with inner margin straight, and outer margin distally strongly convex, with a long seta on outer apical corner; palpomere 3 digitiform, usually shorter and markedly narrower than palpomere 2, with a subapical seta on outer corner. Mentum nearly 1.5-times wider than long, parallel sided, moderately to strongly depressed anteromedially; anterior margin with relatively deep median excision, limited from the ventral surface by a U to V shaped transverse carina. Submentum rather flat; ocular ridge (see Komarek 2004, Fig. 1) well developed (see Fig. 4A). Thorax. Pronotum widest at base, narrowed anteriorly, surface rather evenly convex; ground punctation uniform, moderately fine, sometimes ground punctures connected by fine lines; seta bearing systematic punctures scattered through the surface, particularly noticeable as transverse anterolateral bands. Scutellum of moderate size, triangular, nearly as long as wide. Prosternum (Fig. 5A) well developed, flat, at most only weakly convex, not carinate; anterior margin of prosternum only slightly convex mesally; intercoxal process somewhat triangular (with base facing posteriorly), with surface posteriorly bifurcated. Mesoventrite not fused to mesepisterna, narrowly reaching anterior mesothoracic margin, posteriorly widely elevated; elevation usually with a transverse ridge, variable in shape and sharpness (in Q. dentatus the ridge is produced into a blunt, vertical, median tooth); mesepisternum obliquely widely concave. Mesofurca (examined in Q. clusia and Q. reticulatus ; see Fig. 5B) with short arms, hardly as long as the length of mesocoxae; apex of arms triangular to irregularly explanate. Metaventrite weakly convex, medial posterior portion rather flat, entire metasternum very finely and densely pubescent, without median glabrous patch (reduced in Q. acroreius and Q. dentatus ). Metepisterna approximately three times longer than wide, parallel-sided. Metafurca (examined in Q. clusia and Q. reticulatus ; see Fig. 5C) short and stout, with furcal arms slightly longer than stalk; stalk somewhat triangular (wider near the crux, gradually narrowing distally); outer margins of stalk diverging from base towards midpoint of furcal arms; furcal arms somewhat rectangular, with apex (hemiductus) explanate, obliquely positioned; anterior tendons inserted near midpoint of dorsal edge of furcal arms; dorsal sheaths well developed, as wide as to slightly wider than widest point of lateral sheaths. Elytra. Surface even (without elevations or depressions), with 10 well defined longitudinal rows of serial punctures (see Fig. 6) (except in Q. acroreius and Q. dentatus which have irregularly punctate elytra; see Fig. 1), sutural series rather sharply impressed posteriorly, the remaining series slightly impressed; seta bearing systematic punctures scattered along interstriae; elytral margins slightly explanate anteriorly, increasing to more broadly explanate in posterior third. Epipleura well developed, densely covered by pubescence, rather weakly oblique, relatively wide anteriorly, gradually narrowing towards level of metacoxae, continued as a somewhat narrow stripe to apex; pseudepipleura glabrous, relatively wide throughout, only slightly narrowed posteriorly; surface of pseudepipleura smooth, undulated, anteriorly reticulate or posteriorly canaliculate. Wings (see Hansen 1999, fig. 17; Lawrence and Ślipiński 2013, fig. 23; examined in Q. clusia and Q. reticulatus ) nearly three times longer than wide; radial cell as a pigmented, somewhat triangular area at anterior margin, positioned near mid length of wing; r4, RA3+4 and RA3 reduced; RA3+4 not connected to radial cell; RP2 reduced to a pigmented wide stipe; MP3+4, CuA2 and AA3 reaching margin of wing; basal cell long, reaching a little more than halfway towards posterior wing margin; wedge cell absent; anal (jugal) lobe well developed, narrow, demarcated from remainder of wing by a sharp excision at posterior wing margin. Legs. Pro- and mesofemora with dense pubescence, at most in about basal half, remainder of surface glabrous and shiny, with subtle reticulations; posterior femora mostly glabrous on ventral face, with only scarce scattered long setae over the surface, sometimes with reduced anterobasal, pubescent patch; all femora with rather sharp tibial grooves on inner face except basally. Tibiae moderately slender, rather weakly flattened, with moderately fine and sparse spines. All tarsi with five tarsomeres, bearing 2 (tarsomeres 2-4) to a few (tarsomere 5) long apical hair-like setae on dorsal face; tarsomere 5 without setae or spines on ventral face, tarsomeres 1-4 similar in size and shape; pro- and mesotarsi similar in size and proportions, tarsomeres 1-4 with moderately long and rather dense spiniform setae on ventral face, tarsomere 5 approximately as long as tarsomeres 1-4 combined; meta tarsi 1.3 times longer than pro- and mesotarsi, with tarsomeres 1-4 with 1-2 pairs of spines on ventral face, tarsomere 5 approximately as long as tarsomeres 2-4 combined; claws rather large, moderately curved. Abdomen. Abdomen with 5 ventrites, flat or very weakly convex, all ventrites with uniform, very fine and dense pubescence; first ventrite without median carina, posterior margin of fifth ventrite simply rounded. Aedeagus (Figs 7, 8) with basal piece about half the length of parameres; median lobe wider than base of each paramere, with a narrow, triangular, longitudinal sclerite, usually extending along apical third; parameres as long as, to longer than median lobe, and nearly half as wide; gonopore preapically situated; basal piece with lateral margins straight to sinuate, apically slightly diverging

Larvae: The immature stages are unknown.

Distribution.

Costa Rica (Cartago, Heredia, Limón, Puntarenas), Panama ( Chiriquí, Darién), Ecuador (Napo), Peru (Loreto, Madre de Dios), Venezuela (Amazonas, Bolívar), Guyana, Suriname, French Guiana, Brazil (Amazonas). See Fig. 9B.

Biology.

Extensive collecting data as well as field observations confirm that the genus is terrestrial. While many specimens have been caught using flight intercept traps, many long series have been collected on decaying Clusia fruits. Additional specimens have been collected in rotten logs, sap flows on freshly cut trees, and in the refuse pile of leafcutter ants. The genus has never been collected from aquatic or semiaquatic habitats. It has been found at elevations from 30 to 1600 m. Q. acroreius , Q. dentatus and Q. similaris are not found higher than 350 m, whereas Q. reticulatus is usually found higher than 1000 m.