Phaeoxantha Chaudoir 1850

Genus Phaeoxantha Chaudoir, 1850

Phaeoxantha Chaudoir, 1850: 7.

Type species. Megacephala laminata Perty, 1830: 2 – subsequent type designation by Horn (1915: 433).

Megacephala Latreille, 1802 (partim) – Dejean 1825: 14.

Phoeoxantha (sic!): Lucas 1859: (wrong spelling of the genus-group name).

Megacephala (Phaeoxantha): Horn 1910: 137.

Phaeoxantha: Wiesner 2020: 30.

Ammosia Westwood [in Bates & Westwood], 1852: 51, 57 – synonymy by Chaudoir (1865: 41).

Type species of Ammosia. Megacephala bifasciata Brullé, 1837 – first type designation by Westwood (1853: 218) [the inappropriate subsequent type designation by Horn (1926), choosing M. testudinea Klug, 1834 as a type species of Ammosia, is unavailable].

Note. Phaeoxantha limata (Perty, 1833), based on Megacephala limata, is an unjustified emendation for M. laminata Perty, 1830. Consequently, despite the fact that Horn (1915) used the name M. limata Perty for his subsequent type designation, according to the Articles 67.6 and 69.2, 1 of the ICZN (1999), the type species must be cited in its correct original spelling, thus M. laminata Perty, 1830.

Differential diagnosis. Due to their pale ivory-yellow (sometimes partly almost translucent), ochraceous, cinnamon-ochre to rusty-brownish basic body coloration (mostly with more or less expanded dark brown or black elytral areas) and absence of any metallic-green-blue coloration, the 12 species and one subspecies of the genus immediately differ from all other genera of the tribe Megacephalini Laporte de Castelnau, 1834. Legs mostly concolorous with body. Buccal appendages, particularly both maxillary and labial palpi very long, ivory-yellow to ochraceous.

The genus is here subdivided into two distinctly differentiated subgenera (which due to their distinct differentiating characters may alternatively be treated as two separate genera).

Distribution, ecology and biology. Species of the genus Phaeoxantha are widely distributed in most countries of South America (none of the species penetrates from Colombia to Central America through the Panamanian Isthmus); the countries of their occurrence are mentioned in each individual species below. Majority of them occur throughout the large Amazon Basin and partly also in the area of the Rio de la Plata Basin. Both adults and larvae prefer sandy beaches, semidry or dry riverbeds, but also marshlands. Adults are nocturnal, some of them flightless, several others with only restricted flight ability due to sexually dimorphic development of flight muscle in some species, as observed by Zerm & Adis (2002). Life cycles of adults and larvae of species occurring in open areas of Brazilian Central Amazonian floodplains in the region of Manaus, including larval development (also reared in the laboratory), were presented by Adis et al. (1998), Zerm & Adis (2001a, b, c) and Zerm et al. (2001). Their biotopes in Bolivia were described by Pearson et al. (1999a), and examined species from Bolivia preferred the same biotopes, mostly open sandy beaches or riverbeds of periodical rivers which are usually dry during the day because of strong evaporation in hot sunny days (Ondřej Šafranek. pers. com.). For details see under individual species below. The larvae were partly or with more characters described and illustrated by Arndt et al. (1996), with a key to larvae by Adis et al. (1998) and Arndt et al. (2002) yet no entire habitus of a larval instar was illustrated in the cited papers. Pupal morphology was presented by Cárdenas et al. (2005).

Zerm et al. (2007), in their phylogenetic analysis, based on the nuclear 18S and the mitochondrial 16S and cytochrome oxidase III genes, have concluded that Phaeoxantha species form a monophyletic group of three distinct clades: 1) aequinoctialis – cruciata; 2) limata; 3) klugii – lindemannae – wimmeri. This is in accordance with our concept based on morphology, as well as with our division into the two subgenera as presented here. It must be, however, mentioned here that under the name aequinoctialis the authors studied in fact P. (P.) bifasciata, and under the name limata studied either P. (P.) nocturna or P. (P.) laminata , which were confused at the time of their study.

Key to the two subgenera.

1 Labrum with lateral margins arcuate (Figs 4–7). Mandibles normally shaped in both sexes (Figs 1–3). Body small to medium-sized (length 8.3–19 mm)........................................... Phaeoxantha (Phaeoxantha) Chaudoir, 1850

– Labrum with lateral margins dorsally excised in either side, forming large lateral teeth (Figs 10–12). Male mandibles abnormally shaped, particularly right mandible conspicuously aberrant (Figs 8–9). Body large to very large and mostly robust (length 20–27 mm)........................................................ Phaeoxantha (Euphaeoxantha) subgen nov.