Description of Trypoxylonsicklum sp. nov. from Vietnam and a key to species in the Trypoxylonfulvocollare group (Hymenoptera, Crabronidae)

Abstract Background Trypoxylon Latreille, 1796 (Hymenoptera, Crabronidae) consists of 633 known species worldwide and the genus is divided into numerous species groups. In Vietnam, 19 species of Trypoxylon have been recorded to date. In this study, a new species, Trypoxylonsicklum Pham and Antropov sp. nov. is described and illustrated from Vinh Phuc Province, Vietnam. The new species is the second member of the Trypoxylonfulvocollare species group. A key to species in the Trypoxylonfulvocollaris group is presented. New information Trypoxylonsicklum Pham and Antropov sp. nov., is described as a new species and is the second member of the Trypoxylonfulvocollare species group. A key to species in the Trypoxylonfulvocollaris group is presented.


Introduction
Trypoxylon is worldwide in distribution with 633 described species.These wasps are solitary members of the family Crabronidae (Sann et al. 2018, Pulawski 2023).The genus consists of two subgenera, Trypoxylon and Trypargilum.Whereas the former, consisting of 544 species, is distributed in the Ethiopian, Palearctic, Oriental and Australian Regions, the latter, consisting of 89 species, is distributed only in the Neotropical and Nearctic Regions.Based on external morphological characters and male genitalia structures, Trypoxylon is divided into numerous species groups (Richards 1934, Tsuneki 1978a, Tsuneki 1981, Antropov 1994, Antropov 2003, Antropov 2011).
In Vietnam, Pham et al. (2015) and Pham and Antropov (2021) recorded seven Trypoxylon species.Recently, Pham et al. (2023) have recorded 14 species in North Vietnam, 12 of them being new records.Altogether, 19 species of the genus have been recorded for the country.During a study course of Hymenoptera in 2023 in Vinh Phuc Province, we collected three specimens of a Trypoxylon species.After a closer examination of these specimens, we conclude that they represent a new species and describe it here.Tsuneki (1981) defined the Trypoxylon fulvocollare species group, based on male genitalia characters including the shoulder of the penis valve being almost horizontal; paramere bifurcate at apex; apical lobes of paramere appropriately similar in length; bifurcation deep, reaching top of inner expansion of basiparamere; ventral one of apical lobes of paramere much broader and slightly shorter than dorsal lobe; inner margin of ventral lobe of paramere and that of outer area of basiparamere in a line running straight.The species group previously consisted of a single species, T. fulvocollare Cameron 1904( Tsuneki 1978b,Tsuneki 1979, Tsuneki 1981, Pulawski 2023).The new species described here belongs to this species group as it exhibits the above-mentioned characters, thus representing a second species.Lastly, we present a key to the two species of the Trypoxylon fulvocollare group.

Materials and methods
Sampling was carried out using trap nests, which were placed on horizontal branches, 1 -2.5 m from the ground with their entrances orientated south and north.The trap nests were maintained in the field from 15 to 20 days.Trap nests occupied by Trypoxylon were collected and wasps were reared under laboratory conditions.Adult wasps that emerged from these trap nests were kept, euthanised with a killing jar charged with ethyl acetate, pinned and described with the aid of a light stereomicroscope (Nikon SMZ745).Photographic images were taken using a Nikon SMZ800N microscope camera.Morphological terms used in the text follow Bohart and Menke (1976) and Tsuneki (1979).
Specimens examined including the holotype and the paratype of the new species are deposited in the Institute of Ecology and Biological Resources (IEBR), Vietnam Academy of Science and Technology, Ha Noi, Vietnam.
The following abbreviations are used in the text:
Colour.Body black with following parts yellow: A1-A4; base of A5; band immediately after apical margin of clypeus; base of mandible; maxillary and labial palps; tegula; pronotal collar; pronotal lobe; fore coxa; base of mid-and hind-coxae; fore-and midtrochanters ventrally, femora, tibiae, and tarsi; half of base of hind tibia; lateral sides of petiole, broad base of G2 and G3; apical bands of G1-G5.Following parts ferruginous: apical margin of clypeus; apical two-thirds of mandible; two-thirds of apex of A5, A6-A12; hind trochanter, femur, half apex of tibia and tarsi; half base of petiole dorsally; sides and ventral surface of G6.Veins of wings yellow to brown.
Vestiture.Golden on head and mesosoma, white on metasoma.
Genitalia (Fig. 4D-F).Brownish-yellow, except apical part of sickle black.Penis valve with shoulder, sickle and apical part; shoulder horizontal; sickle conspicuously curved, with its apex distinctly pointed; apical part moderately curved; paramere with two lobes at apex (namely, ventral and dorsal lobes), their length about equal, ventral lobe much broader than dorsal lobe; furrow between two lobes deep, reaching apex of inner expansion of basiparamere; inner margin of ventral lobe and inner margin of outer area of basiparamere in a line moderately curved medially.Dorsal lobe with some long, erect setae apically; ventral lobe with 5-6 long, erect setae at apex, subapical part with several sparse, erect setae along outer margin.

Diagnosis
The new species runs close to T. shakha Tsuneki, 1979 in a key ofTrypoxylon of the Indian subcontinent and Southeast Asia (Tsuneki 1979).In T. shakha and in the newlydescribed species, the females display the following characters: vertex depressed below level of upper eye margin; PAF flat-bottomed; occipital carina complete; propodeum without lateral carinae, dorsal area with furrow; frons, mesoscutum, scutellum, metanotum and propodeum with small sparse punctures.Following parts with yellow integument: A1-A4, pronotal collar, fore-and mid-legs, except broad base of mid-coxa, tergal base of G2-G4, apical bands of G3-G5.Vestiture golden on head and mesosoma.Females of the new species differ from those of T. shakha as follows: Clypeus round apically (in T. shakha, clypeus not round apically, with median margin highly protruded and truncated apically); PAF shallow (in T. shakha, PAF deep); SAT dorsally with medial carina short, not enlarged, not broadly excavated (in T. shakha, SAT dorsally with median carina enlarged into a smooth and round area and broadly excavated); ASR moderately raised (in T. shakha, ASR highly raised, bicarinate on apex); vestiture white on metasoma (in T. shakha, vestiture golden on metasoma).

Etymology
The specific name of this new species refers to the sickle shape of the penis valve.