﻿A remarkable new species of the genus Psammoecus Latreille (Coleoptera, Silvanidae) from Lord Howe Island, Australia

﻿Abstract A new species, Psammoecuslordhowensissp. nov., is described from Lord Howe Island, Australia. The new species is brachypterous and most likely endemic to the island. This species is distinct and can be distinguished by the following morphological characters: body rounded and convex; eyes small; temples well developed; lateral pronotal teeth absent; and hind wing strongly reduced.


Introduction
Lord Howe Island is a small volcanic island (1455 ha) situated in the temperate zone of the Tasman Sea, about 600 km from the east sea coast of Australia (Hutton et al. 2007). It was formed about 6.9 million years ago (McDougall et al. 1981). The native biota of this island is diverse with a high degree of endemism (Hutton et al. 2007). Several endemic genera are present on the island, for example the palms Howea Becc., Hedyscepe H. Wendl. & Drude and Lepidorrhachis (H. Wendl. & Drude) O. F. Cook, a woody composite Lordhowea B. Nord., the tree Negria F. Muell., the leech Quantenobdella Richardson, three annelid genera (Paraplutellus Jamieson, Pericryptodrilus Jamieson and Eastoniella Jamieson), an isopod Stigmops Lillemets & Wilson, a hemipteran bug Howeria Evans and a cricket Howeta Otte & Rentz (Hutton et al. 2007). The native flora includes 241 species, of which 43.6% are endemic (Green 1994). Although over 50% of the terrestrial invertebrates of Lord Howe are probably endemic species (Recher and Ponder 1981), many species still have not been described or recorded (Hutton et al. 2007).
Silvanidae are generally small, cryptic, detritivores, feeding on dead plant material and fungi in closed forests (Lawrence and Ślipiński 2013). The Australian fauna has not been revised, but is known to include about 75 species, many of which are undescribed (Lawrence and Ślipiński 2013). Two Silvanidae are recorded from Lord Howe, Australodendrophagus australis (Erichson) and the cosmopolitan species Cryptamorpha desjardinsii (Guérin-Menéville) (Olliff 1889). Here we describe a third, new species, in Psammoecus Latreille. Psammoecus includes 84 species and is characterized by the securiform distal maxillary palpomere, the simple scutellary shield, lack of a scutellary striole, and the bilobed third tarsomere (Thomas 1984;Thomas and Nearns 2008;McElrath et al. 2023). Although the distribution of most species is restricted to the Old World, two Old World Psammoecus species have been found in the New World: P. trimaculatus Motschulsky from Brazil and P. simonis Grouvelle from the airport of Minnesota, United States (Thomas and Yamamoto 2007;Ouellette 2018). Some Psammoecus species show an extremely wide distribution, which seems to be sometimes caused by human activity (Karner 2020) and several intercepted records at ports or airports with imported materials have been published (e.g., Lu and Han 2006;Ouellette 2018;Yoshida 2020). Seven Psammoecus species are known from Australia, three of which are endemic, but the others may be accidental introductions (Karner 2020). The distinctive new species described here is flightless and almost certainly endemic to Lord Howe Island.

Observation, dissection and photographic techniques
Observations and dissections were performed under a stereomicroscope (Olympus SZX10 or Nikon SMZ1270). Male genital structures were placed on a cavity slide glass with Euparal for observation under an optical microscope (Nikon Eclipse E400). Measurements were made using a digital microscope (Olympus DSX110) with an integrated measuring function and read up to three decimal places in millimeters.
The abdomens of some specimens were removed and soaked in a 10% potassium hydroxide solution at room temperature overnight. After rinsing in water, the soaked abdomen was dissected under a stereomicroscope (Nikon SMZ1270) using fine insect pins, and the genital organs were detached for observation. After observations were completed, the dissected parts were mounted in Euparal on cover glasses which were glued to a piece of cardboard, and pinned with the relevant specimen (Maruyama 2004).
Photographs were taken with a digital camera (Canon EOS 7D) fitted with a macro lens (Canon MP-E 65 mm). Composite images were produced using Affinity Photo version 1.10.6 (Serif Europe Ltd.). Images were retouched using the same software.

Terminology, abbreviations and specimen deposition
Morphological terminology follows Lawrence et al. (2010) and Lawrence et al. (2011). Abbreviations and measurements are as follows:

BL
HL + PL + EL; HL length from anterior margin of clypeus to imaginary line between posterior margins of temples in dorsal view measured along the median line; HW greatest width of head across eyes; IE narrowest width of interspace between eyes; PL length of pronotum measured along the median line; PW greatest width of pronotum, excluding teeth; EL length of elytra measured along suture plus length of scutellar shield; EW greatest combined width of elytra.
Depositories of the examined specimens are as follows:

ANIC
Australian National Insect Collection, CSIRO, Canberra, Australia; AM Australian Museum, Sydney, Australia. Diagnosis. This new species is distinguished from other Psammoecus species by the rounded and convex body shape, small eyes, well-developed temples, the pronotum with irregular crenulation of obtuse tubercles (shorter than wide) not forming obvious teeth, and the extremely reduced hindwing and the male genital morphology. Description. BL: 2.79-3.50 mm (n = 20). Coloration (Fig. 1). Head and pronotum reddish brown. Elytra reddish brown or somewhat lighter colored, with a quadrate or triangular black macula on each elytron at middle, narrowly darkened around humeri and apex of elytra; middle macula and apical darkened area connected by darkened area along lateral margin, also connected by darkened area along suture in darker colored specimens (Fig. 1C). Mouthparts and legs yellowish brown. Antennae reddish brown or somewhat lighter colored, 7 th antennomere dark brown, 8 th to 10 th black, 11 th white; setae golden.
Habitat. Psammoecus lordhowensis is endemic to the Lord Howe main island, where it is widespread in closed temperate rainforest, from the northern (Malabar Ridge) to the southern (Little Slope) end of the island, and from sea level to 530 m elevation. It does not appear to occur in the cloud forest on the summit of Mount Gower (above 700 m). This species is mostly collected by sieving leaf litter, but one specimen was collected in a pitfall trap and another under bark.
Etymology. The specific name of this new species is derived from the type locality, as a noun in genitive case.

Hindwing reduction in the tribe Telephanini
The hindwing of this new species is extremely reduced (brachypterous), which means that it cannot fly. In Psammoecus, brachypterous or apterous species have not been recorded previously. In related genera, four apterous species are known in Telephanus from Jamaica (2 spp.), Reunion Island (1 sp.) and Mexico (1 sp.), and one brachypterous species is known in Cryptamorpha (C. triregia) from the Three Kings Islands, New Zealand (Thomas 1984(Thomas , 1992(Thomas , 2011Brown et al. 2012). Additionally, several flightless species of Telephanini are known from rainforests on the Australian mainland (Lawrence and Ślipiński 2013). The loss of the ability to fly among animals is characteristic of the well-known "island syndrome" (Carlquist 1974;Baeckens and Van Damme 2020). Although, in general, many species of Psammoecus have highflight activity (Karner 2020), this new species has likely reduced its flight activity and lost its functional hindwing in Lord Howe Island.
Which species is most closely related to this new species?
In Psammoecus, the male genital structures (including the spiculum gastrale and the internal sac, which are sometimes overlooked in descriptions) are similar to each other between closely related species (e.g., P. trimaculatus, P. triguttatus Reitter and P. labyrinthicus Yoshida & Hirowatari; P. fasciatus Reitter and P. hiranoi Yoshida & Hirowatari) (Yoshida andHirowatari 2013, 2014;Yoshida et al. 2018;Karner 2020). For identification of these species, it is often necessary to examine male genital morphology. The male genital structure of this new species is similar to those of some Psammoecus species (e.g., P. venustus Karner, P. taiwanensis Yoshida, Karner & Hirowatari). However, due to its distinctive morphology (see Diagnosis), this new species can be distinguished from other congeneric species without examination of its male genital structure. In addition, information on the whole male genital morphology of other Psammoecus species is significantly lacking. Although some species have similar male genitalia to those of this new species, it is difficult to conclude which species is closely related to this new species. To determine the species most closely related to this new species, further studies on the male genital morphology of this genus and the phylogenetic relationships among this genus are required.