﻿The genus Aridelus Marshall (Hymenoptera, Braconidae, Euphorinae) from Japan, with description of a new species

﻿Abstract Six Japanese species belonging to the genus Aridelus Marshall, 1898 (Hymenoptera, Braconidae) were recorded and photographed. Three species, A.dubius Belokobylskij, A.egregius Schmiedeknecht and A.rufotestaceus Tobias (= Aridelusrufiventris Luo & Chen syn. nov.), are new to Japan, and a new species, A.rutilipoidessp. nov. is described. An identification key to the Japanese species of Aridelus is also provided. In addition, new host records are provided, i.e., A.flavicans Chao reared from Homoeocerusunipunctatus and Riptortuspedestris (Alydidae) and A.rufotestaceus reared from Glauciassubpunctatus (Pentatomidae). The Alydidae is a newly recorded host family of Aridelus.


Introduction
The braconid subfamily Euphorinae is unique in attacking a wide range of host orders, including both larvae and adult insects (Stigenberg et al. 2015). Its adult morphology varies greatly, probably due to adaptive evolution, which enables it to utilize a variety of free-living host insects (Shaw 1985(Shaw , 1988Maeto 2018).
The genus Aridelus Marshall, 1887 has an aberrant morphology, that is, the entirely areolate mesosoma and the elongated tubular first metasomal tergite. Using a petiolated metasoma with a short ovipositor, females lay eggs into nymphs or adults of heteropteran stink bugs (Shaw 1985;Maeto and Kudo 1992;Shaw et al. 2001). They are hitherto known to be solitary koinobiont endoparasitoids of the families Acanthosomatidae, Pentatomidae, Plataspidae, and Scutelleridae (Shaw et al. 2001). Although more than 40 species of Aridelus are known worldwide , only two species, A. elasmuchae Maeto &Kudo, 1992 andA. flavicans Chao, 1974, have been recorded in Japan (Maeto and Kudo 1992;Konishi and Maeto 2000).
In our study of Japanese Euphorinae, we identified six species of Aridelus, that is, A. dubius Belokobylskij, 1981, A. egregius (Schmiedeknecht, 1907), A. elasmuchae, A. flavicans, A. rufotestaceus Tobias, 1986, and A. rutilipoides sp. nov. In this study, all Japanese species are photographed, a new species is described, and an identification key to the Japanese species is provided. In addition, new host records of A. flavicans and A.rufotestaceus are presented herein.
Morphological observation was conducted using a stereoscopic microscope (SMZ800N, Nikon, Tokyo, Japan). The specimens were photographed using a digital microscope (VHX-1000, Keyence, Osaka, Japan) with a 10-130× lens. Multi-focus photographs were stacked in the software associated with the Keyence System. The figures were edited using Microsoft PowerPoint 2019.
Colour. Black. Palpi, antenna entirely, mandible, tegula, legs except for telotarsus and first metasomal tergite dark reddish brown; remainder of metasoma reddish brown, telotarsus and veins dark brown; pterostigma pale in basal 1/5 or faintly pale basally. Fore wing hyaline with two fuscous bands. Hind wing with a fuscous band in its apical third.
Remarks. This species was described with only the male holotype available. The Japanese specimens mostly agree well with the original description (Belokobylskij 1981) and run in the key by Belokobylskij (2000) to A. dubius. The redescription of this species based on Japanese female specimens is represented here.
This species resembles A. rutilipes Papp described from Taiwan ( Fig. 6) but differs in having the distinct malar suture (absent in rutilipes), the palpi dark reddish brown (light reddish brown in rutilipes), the apical hyaline area of the fore wing comparatively small, not reaching the apex of marginal cell (Fig. 1F) and the apico-posterior edge of the fore wing (in rutilipes comparatively large, almost reaching the apex of marginal cell and reaching the apico-posterior edge (Fig. 6A)), and the metasoma reddish brown to dark reddish brown ( Fig. 1A) (dark brown in rutilipes (Fig. 6A)). Fig. 2A  ). New to Japan.

Discussion
Among the six Japanese species, A. egregius and A. rufotestaceus are widely distributed in the Palaearctic region, but four other species (A. dubius, A. elasmuchae, A. flavicans, and A. rutilipoides sp. nov.) are virtually confined to East Asia (China, Japan, Korea, the Russian Far East and Taiwan). Two Japanese species, A. rutilipoides sp. nov. and A. dubius, have a comparatively larger body and the fore wing with two fuscous bands and belong to a species complex with A. rutilipes from continental China, Korea, and Taiwan, and A. ussuriensis from continental China, Korea, and the Russian Far East. A comprehensive study on the fauna and phylogeny of Aridelus in and around East Asia is required.
All previously known host families of Aridelus (Acanthosomatidae, Pentatomidae, Plataspidae, Scutelleridae) belong to the superfamily Pentatomoidea (Shaw et al. 2001), but our study has revealed that Aridelus can also use the superfamily Coreoidea (including Alydidae) as host insects. While the most widely distributed species, A. egregius, is known to parasitize three host families, other Japanese species so far only one host family is known present study). The host specificity of Aridelus species is an interesting problem that deserves further study.