Four new species of Trigonopterus Fauvel from the island of New Britain (Coleoptera, Curculionidae)

Abstract The hyperdiverse genus Trigonopterus has its center of diversity in Melanesia, but only a single species is recorded from the Bismarck Archipelago to date. Here we describe four new species from the island of New Britain: Trigonopterus chewbacca sp. n., Trigonopterus obsidianus sp. n., Trigonopterus puncticollis sp. n. and Trigonopterus silaliensis sp. n. We provide cytochrome oxidase subunit I (cox1) sequences of the new species and a key to all five species known from the Bismarck Archipelago.


Introduction
Trigonopterus Fauvel is a genus of flightless weevils of the subfamily Cryptorhynchinae (Alonso-Zarazaga and Lyal 1999). It is distributed in Southeast Asia (Riedel et al. 2014), Australia (Riedel and Tänzler 2016) and Melanesia, with its center of diversity in New Guinea (Riedel et al. 2010;Tänzler et al. 2012, Riedel et al. 2013b). Despite Trigonopterus being recorded from the remote islands of Fiji (Zimmerman 1938b), Samoa (Marshall 1931) and New Caledonia (Heller 1916), only one species has been described from the Bismarck Archipelago to date, i.e. Trigonopterus pembertoni (Zimmerman 1938a) from New Ireland. Here we describe four new species from the island of New Britain. Presumably, there are many additional new species to be found on this island. Unfortunately, large expanses of low-elevation forests in New Britain have been converted to oil-palm plantations, highlighting the significance of documenting the insect fauna before the remaining forests are gone.

Materials and methods
This study is based on 18 specimens, the result of a ten-day expedition to the area east of Silali Village in the Nakanai Range of West New Britain during November of 2014 by the first two authors. Specimens were collected by beating foliage and by sifting of leaf litter with subsequent extraction of specimens using Winkler eclectors (Besuchet et al. 1987). Holotypes were selected from the ten sequenced specimens; their DNA was non-destructively extracted as described by Riedel et al. (2010). Preparation of genitalia follows the method described by Riedel et al. (2014). Illustrations of habitus and genitalia are of holotypes.
Type depositories are cited using the following codes: ANIC Australian National Insect Collection, Canberra, Australia SMNK Staatliches Museum für Naturkunde, Karlsruhe, Germany. ZSM Zoologische Staatssammlung, München, Germany. UPNG University of Papua New Guinea, Entomology Collection DNA sequencing and sequence analysis follows the method described by Riedel et al. (2010) and Tänzler et al. (2012). In the diagnostic descriptions, only the major characters are given, as in the format outlined by Riedel et al. (2013a, b).
Specimens were studied under a Leica MZ16 dissecting microscope and a fluorescent desk lamp for illumination. Measurements were taken using an ocular grid. Body length was measured in dorsal aspect from the elytral apex to the front of the pronotum, and elytral width between the humeri at their greatest extent and across both elytra. Legs were described in an idealized, laterally extended position; there is a dorsal / ventral and an anterior / posterior surface. Habitus illustrations were prepared by photographing the specimens with a DFC450 camera with L.A.S. 4.6.0 software mounted on a Z6 APO (all from Leica Microsystems, Heerbrugg, Switzerland). Photographs of the genitalia were taken under an Axio Imager M2 microscope (Carl Zeiss Microscopy) equipped with 5X or 10X A-Plan lenses and with a JVC KY70 camera (JVC Professional Products); the resulting image stacks were combined using the Helicon Focus 6.2.2 software (Helicon Soft Ltd). For this purpose the genitalia were embedded in glycerol gelatin, as described by Riedel (2005). The genitalia were photographed with their longitudinal axis somewhat raised at the posterior end, to adequately illustrate the structures of the curved apex. All photographs were enhanced using Adobe Photoshop CS2. Sequence data were submitted to the GenBank, and the accession numbers are provided under each species e.g. as "(GenBank # KU888894)".
Notes. Presumably, the species belongs in the T. basalis-group of Riedel et al. (2013b).
Notes. This species belongs to the T. politus-group of Riedel et al. (2013b) and is similar to T. politus (Faust) of the Papuan Peninsula. It can be distinguished by the symmetrical apex of the penis and the less distinct denticles of the male metatibia.

Discussion
The absence of a record of a weevil genus from a Melanesian island is often difficult to interpret, i.e. it is usually unclear whether this is based on a true absence or on a lack of records. Prior to this study, Trigonopterus was unknown from New Britain. The four species described here represent four different clades of Trigonopterus, indicating that the oceanic island of New Britain has been colonized at least four times, and T. pembertoni, which occurs on neighboring New Ireland and represents the T. oblongus-group, brings the number of colonization events of Trigonopterus in the Bismarck Archipelago to five. Given the size, mountainous topography and tropical vegetation of New Britain, it is likely that Trigonopterus has undergone some local speciation on the island, but this possibility requires further investigation. Despite many days of searching for Trigonopterus in primary forest on New Britain, the weevils were quite scarce in comparison with similar localities on the New-Guinean mainland. This scarcity may be due to the local conditions or seasonal effects, as orographic precipitation formed early in the day and continued into the evening during our stay. The specimens' habitat consisted of primary forest growing on a limestone karst.