Phrixosoma concavifrons Jordal

Jordal, Bjarte H., 2012, Phrixosoma concavifrons – a sexually dimorphic Phrixosomatini (Coleoptera: Curculionidae) from the Udzungwa mountains in Tanzania, Zootaxa 3255, pp. 52-56 : 53-56

Phrixosoma concavifrons Jordal , sp. nov.

( Figs. 1 , 2 )

Diagnosis: This is a unique species in Phrixosoma due to the strongly concave female frons with a long tuft of golden setae along the upper margin of the concavity.

Description: Length 1.85–2.10 mm, 2.0–2.1 times longer than wide. Head. Female frons broadly concave from well above upper level of eyes to epistoma, surface strongly reticulated, dull; vestiture consisting of long protruding golden setae along upper rim of frontal concavity down to upper level of eyes, continuing along lateral margin to epistoma as much shorter erect setae. Female eyes separated above by 3.1–3.2 times their width. Male frons weakly flattened, with a distinct narrow median carina from vertex to epistoma; vestiture modest, consisting of short hair-like setae. Male eyes separated above by 2.4–2.5 times their width. Antennal club flat, three sutures clearly marked by setae, first and second suture slightly angulate, first suture marked by a partial septum running two-thirds the length of entire suture; scapus with few setae, about three-quarter the length of club and funiculus combined. Pronotum 0.7–0.8 times as long as wide, broadest at base, curved anteriorly to a distinct constriction at anterior third; surface rugosely granulated, punctures absent; vestiture consisting of erect bristle-like setae which are longer towards the centre of notum. Elytra 1.4–1.5 times longer than wide, 2.0–2.2 times longer than pronotum, sides slightly oval, broadest at middle, narrowly rounded behind. Striae narrow, deeply impressed forming a sharp line, punctures elongated, irregular in size and depth. Interstriae 3–4 times wider than striae, flat, rugosely granulated, granules increasing in size posteriorly. Interstriae 10 elevated to the level of metacoxae. Vestiture consisting of three interstrial rows of curved pointed setae, setae in mid-row three times longer and uniseriate; strial setae present, very thin. Hind wing (see Jordal, 2009; Kukalova-Peck and Lawrence, 1993) on costa close to wing base with two short and closely placed setae, stigmal patch without setae; hind margin from level of CuA to tip with fine short setae. Legs. Mesocoxae separated by three times the width of scapus. Metacoxae separated by 1.5 times the width of scapus. Protibiae armed by four socketed teeth at expanded lateroapical angle; on anterior side a deep groove for retraction of tarsus. Mesotibiae with 5 socketed teeth along its lateral distal half, 4–6 smaller spines on remaining proximal half. Metatibiae with a pointed lateral extension on apical one-fifth armed by 2–3 socketed teeth, apically armed by 5–7 socketed teeth in a transverse row on the outer edge; apex concave with a sharp longitudinal flange separating tarsal socket and outer fringe of socketed teeth forming a corbel-like structure. Vestiture on ventral sclerites. Setae on metanepimeron trifid; on metasternum fine long setae, on venter consisting of transverse rows of long erect bristle-like setae on ventrites I–IV, with ground vestiture consisting of fine tri- to pentafid setae. Proventriculus as in P. m i n or ( Lopez-Buenfil et al., 2001). Terminalia. Aedeagus 5.1 times longer than wide, apex incised as a cleft, aedeagal body with a raised spiral shaped sclerite close to apex; apophyses very short, 0.15 as long as aedeagal body. Tegmen a closed ring, with distinct anterior strut (manubrium) slightly shorter than the apophyses. Spiculum gastrale as long as aedeagus, gently curved from apex towards level of tegmen, continue in straight line to anterior end of apohyses. Spermatheca with collum protruded, wrinkled, broadly separated from ramus; cornu apically broadly rounded, curved about 90 degrees from corpus.

Material examined. Holotype female: “ TANZANIA, Morogoro prov., Sanje, GIS: −7.767, 36.868, ex fallen tree [6vii- 2], 6. July 2010, B. Jordal, leg”. Allotype male, 2 male and 3 female paratypes: same label as holotype. Two additional badly preserved specimens (1 male, 1 female) with the following label: “ TANZANIA, Morogoro prov., Sanje, GIS: −7.767, 36.868, ex old log [5vii- 4], 5. July 2010, B. Jordal, leg”. The holotype and all other material are deposited at the entomological collection, University Museum of Bergen.

Etymology: named by the strongly concave frons in the female.

Discussion: The new species has been compared to all African species of the genus ( P. fuscovillosa , P. garciniae , P. sinuosa , P. dubiosa , P. quadrioculata , P. uniseriata , P. major , P. nigra , P. psaltes , P. costata ) and four Neotropical species (P. m i n o r, P. r u d e, P. o b e s a, P. c l u s i a e), from which it clearly differ by the strongly concave female frons and by the longer middle row of interstrial setae. This is the first observation of such strong sexual dimorphism in the genus ( Wood, 2007). It is nevertheless a typical Phrixosoma by all other morphological features: the male has a longitudinal carina in frons as most other species of the genus, the antennal funicle is 6-segmented, the club has a partial septum at the first suture, the eyes are divided, the interstriae has the typical flat and granulated structure with an abrupt transition to the narrow striae, and the metatibiae bears the characteristic incision between a lateral bundle of closely set lateral teeth and the distal row of smaller socketed teeth. The corbel-like apex of the metatibiae is a quite unique feature for Phrixosoma , only seen in Hylastini and a few other groups. Internal characters such as the male genitalia and the proventriculus are very similar to other species of Phrixosoma such as the Neotropical P. minor and the West African P. uniseriata . The male genitalia are particularly informative, as the very short apophyses are unique in Scolytinae . Furthermore, genetic data from four nuclear and one mitochondrial gene show that P. concavifrons is nested within the genus (Jordal & Cognato, unpublished manuscript).

Biology and distribution: This species is known only from two nearby localities at 1700 m altitude in the Udzungwa Mountains of Tanzania. Specimens were taken from very thick bark of a densely colonised host tree of diameter 15–30 cm, and were collected together with a small species of Polygraphus . Males and females join as monogamous pairs in a mating niche (nuptial chamber) with the female subsequently laying eggs in pits along a transversely cut biramous tunnel system which was 1–2 cm long. The male apparently stays with the female during egg laying, and probably stay longer such as in the males of P. uniseriata , which stay at least to late larval stage (unpublished data). Brood size ranged from 30– 50 larvae (n=9). The larvae make regular mines more or less perpendicular to the egg gallery.

Figures

FIGURE 1. Dorsal, frontal and lateral views of Phrixosoma concavifrons sp. n. female (A – C) and male (D), and P. uniseriata (Eggers) (E – G).

FIGURE 2. A, Phrixosoma uniseriata male genitalia, dorsal and lateral view. B – J, P. concavifrons sp. n: B, male genitalia, dorsal and lateral view; C, spermatheca; D, labium, dorsal (inner) and lateral view; E, antenna; F, protibia; G, mesotibia; H, metatibia; I, apical view of metatibia; J, mesosternal process.