Xystosomus gruti Bates 1871
Creators: name: Erwin, Terry L.
Publisher: name: Zenodo
Year: 1973
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Carabidae
Xystosomus
Xystosomus gruti

description: <i>FIGURES</i> 3, <i>22 a-c,</i> 23 24, 36, 69 <i>Xystosomus</i> grutii Bates, 1871a:248. [Lectotype, female, in <b>MHNP,</b> here selected. Type-locality: Rio de Janeiro, Brazil. <b>]</b> <i>Xystosomus</i> hilaris Bates, 1871b:266. [Holotype, male, in MHNP (<i>a</i> specimen mentioned by Bates). Type-locality: <i>Ega</i> (Teffe), Brazil. New synonymy.] Xystosomus belti Bates, 1878:601. [Lectotype, male, in MHNP, here selected. Type-locality: Chontales, Nicaragua. New synonymy.] <i>Xystosomus</i> olivaceus Bates, 1878:601. [Holotype, female, in <b>MHNP</b>, a specimen mentioned by Bates, 1882:147, where <b>he</b> recognized his species as a color aberration of <i>X. belti</i> Bates. Type-locality: Chontales, Nicaragua.] DESCRIPTION.—Form (Figure 3): Large, broad, moderately convex (much less so than members of <i>laevis</i> group) with large head, narrow pronotum (compared with members of <i>laevis group</i>), <i>and</i> fully striate elytra. A variable species (see below) and easily distinguished from the similar <i>X</i>. ampliatus by the deeper lateral striae and the green metallic luster of the entire dorsal surface of the pronotum and elytra. <i>Color:</i> Head and venter rufopiceous; pronotum and elytra dorsally with metallic green luster; appendages testaceous or partly infuscated. <i>Head:</i> Broad between eyes; frontal furrows moderately impressed; eyes very large and prominent. <i>Pronotum</i> (Figure 3): <i>Transverse</i> (W/ <i>L</i>, x 1.60; range, 1.41-1.85; 69 specimens); lateral setigerous pores present just anterior to middle and at hind angles; laterobasal carina well developed; hind angles about 90° and sharp; side margins broadly explanate and more or less straight to apical third. <i>Elytra:</i> Striae 1-8 of each elytron well impressed and punctulate, sutural stria and lateral four striae more deeply impressed and more coarsely punctulate than striae 2-4; side margins broadly explanate; humeral projection well developed, blunt; chaetotaxy formula Eo-la, 2b, 3b, 4c, 5a, 6a, 7, 8a, and <i>Ed-</i> 1, 7b, 8; plica well developed externally. <i>Microsculpture:</i> Frons (Figure 22 <i>a</i>) with wellimpressed, nearly isodiametric reticulation; pronotum (Figure <i>22b</i>) and elytra (Figure 22 <i>c</i>) with fine transverse lines which fork but do not form meshes. <i>Secondary sexual characters:</i> Male genitalia characteristic of the species group (Figure 23). Female genitalia characteristic of the species group (Figure 36). <i>Size:</i> Sixty-nine specimens: length, 3.7-5.2 mm; width, 1.9-2.5 mm. VARIATION.—The depth of the elytral striae varies from deep to shallow. Northern South America (Peru) is a center for specimens with deep striae. To the north of this center, shallow or deep striae are found on Central American specimens, but only shallow striae are found on the Mexican specimens. To the south, either shallow or deep striae are found on the Brazilian specimens. Many more samples are needed to accurately assess this characteristic, but from preliminary data it appears that depth of striae is bimodal with shallower striae in the more temperate climates of the species' range. Slight variation occurs in the shape of the apex of the male median lobe of the genitalia (Figures 23, 24). This variation appears within population samples, however, and is not correlated with <b>geographical</b> area. The great difference in size (see above) is also independent of geographical area. Both large and small individuals were collected in Costa Rica <b>and</b> Panama. All specimens from Brazil are large, but this may be sample bias, <b>as</b> there <b>are</b> only nine specimens. <i>NATURAL</i> HISTORY.— <i>In</i> August, in Mexico, George Ball and I collected a male specimen that we saw running on the sun-lit bark of a fallen and partially burnt "buttress tree" after we <b>disturbed</b> some bracket fungi. On <b>Barro</b> Colorado Island, in December, my wife and I collected a female specimen in a pile of deep loose leaves under the crown of a recently fallen tree. The latter beetle was in the company of X. nigripalpis (see below for details). <i>F</i>. Nevermann's excellent collecting records pinned with each specimen give the following data (translated from <b>German</b>): "on leaf pile in sawmill, June," 2 <i>specimens</i>; "on leaves of <i>Cedrela</i> mexicana, May" (Meliaceae), 4 <b>specimens</b>; "on wilted foliage of <i>Quararibae</i> turbinata, October" (Bombacaceae), 10 specimens; "on dry wood of <i>Pentaclethra filamentosa,</i> March" (Leguminosae), 1 specimen; "on dry wood of <i>Virola</i> war- <i>burgii,</i> February" (Myristicaceae), 2 specimens; "under loose bark, November and June," 4 specimens; "wilted leaf of <i>Acanthorhiza sp</i>., June" (Phoenicaceae), 1 specimen; "at fermenting plant juice on freshly cut wood, August," 5 specimens; "at light, <i>July</i>," 1 <i>specimen</i>. I have observed a captive female from Barro Colorado Island in flight. Further records indicate specimens were collected in September in Brazil, but no teneral specimens were seen to indicate at what season immatures might be discovered. The altitudinal range of <i>X</i>. gruti is from near sea level on Barro Colorado Island to about 4,000 feet (1,219 m) on Volcan de Chiriquf, with most intermediate elevations represented on specimen labels. In summary, this is a widespread and variable species <i>occurring</i> at low and medium elevations. In habits, it is probably arboreal, or at least subarboreal, and <i>is</i> capable of flight. Adults were collected in every month except January and April. It is probable that adults and immatures overlap. BEHAVIOR.—The specimen from Barro Colorado Island was collected alive and was returned to Washington for further study (it is still alive at this writing). With only one individual, intraspecific reactions are not possible, but when this specimen and X. nigripalpis specimens are placed together in the same petri dish both demonstrate fierce aggressiveness. This reaction also occurs between members of <i>X</i>. nigripalpis and happens when two beetles come within "setal range" of each other (the elytral "Eo" setae on these beetles are very long). <i>The</i> result of contact is several quick lunges with the mandibles directed toward the other beetle. <i>Many</i> of my living <i>specimens</i> of <i>X</i>. nigripalpis are missing the apical articles of the antennae. DISTRIBUTION (<i>Figure</i> 69).—The range of this species extends from <i>Vera</i> Cruz, <i>Mexico</i>, to <i>Rio <i>de</i> Janeiro, <i>Brazil</i>. <i>Throughout</i> the range these beetles are distributed both at lower and middle elevations and in lowland tropical forests and cloud forests.</i> LOCALITY RECORDS (Figure 69).—I have seen at least 74 specimens (old cotypes in BMNH and MHNP not counted) from the following localities: <i>MEXICO</i>: VERACRUZ: 2.5 miles west of Sontecomapan <b>(</b> UASM <b>); C</b> 6rdoba <b>(MHNP).</b> CENTRAL <b>AMERICA:</b> BRITISH HONDURAS: Toledo District <b>(</b> MCZ <b>).</b> COSTA RICA: Hamburg Farm at Reventaz6 <b>n</b> <b>(</b> USNM <b>);</b> Iberia Farm in Santa Clara Province <b>(</b> USNM <b>);</b> Las Mercedes <b>(</b> USNM <b>).</b> <i>NICARAGUA</i>: Chontales <b>(</b> MHNP <b>).</b> PANAMA: <b>Barro</b> Colorado <b>Island</b> in Canal Zone <b>(</b> USNM <b>);</b> Bugaba <b>(</b> BMNH, MHNP <b>);</b> Cabima <b>(</b> USNM <b>);</b> Volcan de Chiriqui <b>(</b> BMNH, MHNP <b>).</b> SOUTH <i>AMERICA</i>: BRAZIL: Amazonas Province: Teffe <b>(</b> MHNP <b>);</b> Itaituba <b>(</b> MHNP <b>).</b> Para Province: Para <b>(</b> MHNP <b>).</b> Rio de Janeiro Province: Lagoa de Saquarema <b>(</b> MHNP <b>); "</b> Rio Janeiro <b>" (</b> MHNP <b>);</b> Rio Parahyba <b>(</b> MHNP <b>).</b> Santa Catarina Province: Hansa <b>(</b> MHNP <b>).</b> FRENCH <i>GUIANA</i>: Gourdonville <b>(</b> MHNP <b>).</b> PERU: Monson Valley at Tingo Maria <b>(</b> <i>CAS</i> <b>).</b>
description: Published as part of <i>Erwin, Terry L., 1973, Studies of the subtribe Tachyina (Coleoptera: Carabidae: Bembidiini), Part I: A revision of the Neotropical genus Xystosomus Schaum, pp. 1-39 in Smithsonian Contributions to Zoology 140</i> on pages 8-9, DOI: 10.5479/si.00810282.140, http://zenodo.org/record/3828531