Acratheus, DISTANT, 1910

Tatarnic, Nikolai J. & Cassis, Gerasimos, 2012, The Halticini of the world (Insecta: Heteroptera: Miridae: Orthotylinae): generic reclassification, phylogeny, and host plant associations, Zoological Journal of the Linnean Society 164 (3), pp. 558-658 : 571-573

ACRATHEUS DISTANT ( FIGS 3 , 5–6 )

Acratheus Distant, 1910a: 16 (gen. nov. type species: Acratheus nocturnus Distant, 1910 by monotypy); Distant, 1910b: 284 ( India); Reuter, 1910: 161 (cat.); Carvalho, 1952: 73 (list); Carvalho, 1955: 67 (key); Carvalho, 1958: 6 (cat.), Linnavuori, 1994: 7 [diagnosis (diag.), key to spp.]; Schuh, 1995: 45 (cat.)

Diagnosis: Acratheus is distinguished from other Halticini except Nanniella by the densely punctate scutellum, pronotum, and thoracic pleura. It differs from Nanniella by the lack of deep punctures on the frons and vertex and the shape of the left paramere, which in Nanniella is more elongate and apically barbed.

Redescription: Macropterous, body length 2–3 mm. Coloration ( Fig. 3 ): mostly dark brown to black, with yellow or yellow-brown markings. Surface and vestiture ( Figs 3 , 5A–H ): head mostly smooth with shallow punctures limited to genae ( Fig. 5A–C ). Pronotum, scutellum, and thoracic pleura densely punctate ( Figs 3 , 5A–C, E–F ) Hemelytra densely punctate, less so towards apex of corium ( Figs 3 , 5A ); cuneus punctate. Abdominal sternites with few punctures laterally ( Fig. 5H ). Thorax and abdomen sparsely covered with longish, brown, decumbent setae ( Fig. 5B, E, H ). Structure: body elongate and slightly ovate. Head ( Figs 3 , 5A–C ): transverse, short, taller than wide; eyes large, height of gena slightly greater than eye height; posterior margin of vertex carinate, sublinear with eyes not touching pronotum; vertex convex; clypeus not distinctly projecting forward; maxillary plate long and vertical; bucculae small, narrow. Antennae ( Figs 3 , 5A–C ): insertion in line with midpoint of eye; elongate, narrow, AI only slightly thicker than AII. Labium ( Fig. 5B ): extending beyond metacoxae, LI somewhat swollen and elongate; thorax ( Figs 3 , 5B, D–F ): pronotum trapezoidal, steeply inclined, collar flat, visible from above, posthumeral angles distinctly depressed, posterior margin carinate, medially concave; mesoscutum visible; scutellum medially raised, basally depressed, laterally declivent; metathoracic spiracle exposed, operculum large, without evaporative bodies; MTG external efferent system reduced, tongue-like, peritreme located along posterior margin of metepisternum, narrow strip of evaporative areas anteriad to peritreme. Hemelytra ( Figs 3 , 5A ): Laterally declivent at corial fracture, lateral margin slightly flared apically; membrane extending beyond abdomen. Legs ( Figs 3 , 5G ): elongate, narrow; metafemora not incrassate; pretarsi without pulvilli. Abdomen: elongate-ovoid. Male genitalia ( Figs 6A–C , 5H ): pygophore conical, simple, without modifications or processes; parameres subequal in length, both with elongate sensory lobe; left paramere broad, with thin, strongly arcuate distal arm; right paramere spoon-shaped with thin apical apophysis, projecting beyond genital opening of pygophore; phallotheca simple, elongate, abruptly narrowing from midpoint to apex; ductus seminis short, with irregular U-shaped sclerotized secondary gonopore, opening into a conical sclerotized tube running length of phallotheca. Female genitalia ( Fig. 6D, E ): sclerotized rings minute, thin, lateral margins and adjacent portion of DLP weakly upturned; posterior wall membranous, with very weak lateral swellings; margins of vestibulum symmetrical with medial margins of first gonapophyses forming slightly tumescent, weakly sclerotized plates.

Diversity and distribution: Acratheus has four species, two in India and two in equatorial Africa. Lack of records despite intensive sampling in Middle Asia by Linnavuori (1975, 1984, 1986, 1992) suggests this apparent geographical disjunction is real.

Included species: Acratheus albipes ( Motschulsky, 1863) India

Acratheus nocturnus Distant, 1910 India

Acratheus ocellaris Linnavuori, 1994 * Benin; Ivory Coast; Nigeria; Togo

Acratheus punctiger ( Linnavuori, 1975) * Benin; Nigeria; Sudan; Upper Volta

Biology and host plant associations: Acratheus is found on undergrowth in savannah and rain forests ( Linnavuori, 1994). No host plants have been recorded for this genus.

Remarks: Acratheus is one of only two halticine genera characterized by deep punctations on the head, pronotum, thoracic pleura, and hemelyra, the other being the endemic African genus Nanniella . Schuh (1974) first proposed a close relationship between these genera. In contrast, Linnavuori (1994) stressed that Nanniella ‘undoubtedly represents a separate evolutionary lineage’, and posited that Acratheus and Halticus are closely related, based on the following shared similarities: an elongate head, swollen first labial segment (LI), and halticine-type parameres. He also noted that in Nanniella the head is notably shorter and LI is only slightly thicker than LII.

Based on our observations and phylogenetic results ( Figs 1 , 2 ), we concur with Schuh (1974) that Acratheus and Nanniella are closely related, and do not see the differences suggested by Linnavuori. The head projects forward only a little more and the first labial segment is only slightly less thick in Nanniella than in Acratheus . Conversely, both genera share many characters, with the following significant similarities: the posterior margin of the pronotum is concave; the configuration of the external efferent system of the metathoracic gland; the secondary gonopore is wide and distally modified into a sclerotized tube running the length of the phallotheca; the shape of the parameres; the posterior wall of the bursa copulatrix is membranous to weakly sclerotized, bearing two minor lateral swellings; and the sclerotized rings of the female dorsal labiate plate are weakly sclerotized and upturned laterally.

This redescription of Acratheus is based on examination of the African species ( Ac. ocellaris and Ac. punctiger ) and the literature ( Linnavuori, 1994). We did not have access to the Indian species Ac. albipes and Ac. nocturnus ; however, Linnavuori (1994) described the parameres of the former species, which are very similar to the African species.

Figures

Figure 1. Strict consensus of three equally parsimonious trees under equal weighting. Numbers above branches are jackknife support (36% removal probability, values below 50% not shown); numbers below are Bremer support values.

Figure 2. Implied weighting phylogeny (k = 3). Unambiguous character optimizations are indicated by circles: filled circles indicate synapomorphies, white circles indicate homoplasies. Numbers above and below circles indicate character number and state, respectively. Large red numbers above branches indicate jackknife support (values below 50% not reported).

Figure 3. Photographs of Halticini genera: Acratheus–Halticus. Abbreviations: F, female; M, male.

Figure 5. Scanning electron micrograph images of Acratheus ocellaris. A, dorsum; B, head and thorax, lateral view; C, head, dorsal view; D, detail of evaporative bodies; E, thoracic pleura; F, external efferent system of the metathoracic scent gland; G, tarsus; H, pygophore.

Figure 6. Male and female genitalia of Acratheus ocellaris. A, aedeagus; B, left paramere; C, right paramere; D, bursa copulatrix, dorsal view; E, first gonapophyses; F, posterior wall. Abbreviations: DS, ductus seminis; PB, phallobase; PT, phallotheca; SG, secondary gonopore; SR, sclerotized ring.