Rhadinoscelidia lixa sp. nov. (Hymenoptera, Chrysididae, Loboscelidiinae) found on an ant nest in Thailand

Abstract Rhadinoscelidia lixasp. nov. is described from Thailand. It is the fifth species of the genus and second species from Thailand. A biological note on the species with its associated ants is provided.


Introduction
Loboscelidiinae are rare and morphologically peculiar chrysidid wasps. The subfamily contains two genera, Loboscelidia Westwood, 1874 and Rhadinoscelidia Kimsey, 1988. To date, Rhadinoscelidia is known by four species from Hainan Island (China), Thailand, Laos, West Java (Indonesia), and peninsular Malaysia (Kojima and Ubaidillah 2003;Liu et al. 2011;Kimsey 2018). The genus is similar to Loboscelidia in some morphological characters; however, Rhadinoscelidia can be distinguished from Loboscelidia by the following characters: cervical expansion separated from upper gena with reduced patches of ribbon-like setae, reduced wing venation of the forewing, and reduced flanges on the legs (Kimsey 2018). Although nothing is known about their biology, the genus Loboscelidia is considered as an egg parasitoid of stick insects, similar to the Amiseginae, and the bizarre structural modification implies their myrmecophily (Riek 1970;Krombein 1983;Kimsey 2012). During the investigation of chrysidid fauna of Southeast Asia, we had a chance to examine an unidentified female of Rhadinoscelidia from Thailand. This wasp was found staying at the nest entrance of the ant species Carebara diversa (Jerdon, 1851) (Formicidae, Myrmicinae).
In this paper, we describe it as a new species of Rhadinoscelidia and provide a key to known species, and a brief discussion on the life history, of the genus.

Materials and methods
The material used in this study is deposited in the Entomological Laboratory, Faculty of Agriculture, Kyushu University, Japan. Images were taken with a Canon EOS Kiss X8i camera and edited using Adobe Photoshop CC. Morphological terminology and measurements mainly follows Kimsey (1988Kimsey ( , 2018 and Liu et al. (2011). The following abbreviations and indices were used: maximum length of median ocellus diameter (MOD), minimum length of postocellar line (POL), minimum length of ocello-ocular line (OOL), maximum length of lateral ocellus diameter (LOD), lateral ocellar line (LOL, Masner and Huggert 1989) is the shortest distance between the inner margins of median and lateral ocelli, segment of flagellomere (F), metasomal tergite (T), and metasomal sternite (S).

Taxonomy
Rhadinoscelidia Kimsey, 1988 Diagnosis. Antennal scape distinctly longer than head; vertex sharply declivous behind ocelli; cervical expansion of head with posterior shield-like expansion clearly separate from rest of head; forewing venation highly reduced, restricted to basal sixth or less; all tibiae without flanges.
Male. Unknown. Etymology. Named after the Latin 'lixa', meaning camp-follower, referring to the wasp walking near the ant's trail.

Distribution. Thailand (Phrae).
Associate. Carebara diversa (Hymenoptera, Formicidae) (Fig. 8). Remarks. Rhadinoscelidia lixa sp. nov. is easily distinguished from other species by the following characters: scape 4.3 times as long as width (over 5 times as long as width in other species); short erect setae of antenna; wide ribbon-like setae on temple wider than those on pronotum (shorter than those on pronotum in other species); shorter ribbon-like setae on cervical expansion (relatively longer in other species); straight hindtibia (slightly or moderately curved hindtibia in other species).

Discussion
Comparing Rhadinoscelidia lixa sp. nov. with the other four species of Rhadinoscelidia, the morphological characteristics of R. lixa sp. nov. are more conservative, rather similar to those of the genus Loboscelidia. In Loboscelidia, there is one record from the nest of the ant Rhytidoponera metallica (Smith, 1858) (Riek 1970). However, no information on the biology of Rhadinoscelidia has been reported until now (Kimsey 2018). According to observations by the collector, the holotype of R. lixa sp. nov. stayed at the entrance of the nest of Carebara diversa, and it was not attacked by ants. However, the wings of R. lixa sp. nov. were cut off from the basal portion (Fig. 7), probably by ants. Even though this is a singular observation, this may explain why Rhadinoscelidia has rarely been collected by previous trap-based surveys. Sometimes, ants attack the wings of the ant-associate wasps. For example, Paralipsis enervis (Nees) (Braconidae) and Bruchopria hexatoma Kieffer (Diapriidae) have fully developed wings, but wings are eventually cut off by ants after entering the nest (Starý 1966;Loiácono et al. 2002). Similarly, Takada and Hashimoto (1985) reported that Paralipsis eikoae (Yasumatsu), an associate of Lasius japonicus Santschi (L. niger (Linnaeus)), had mutilated wings probably caused by ants. These myrmecophilous wasps show strong adaptation to the host ant, including the nutrition change and the mimicry of the cuticular hydrocarbons. As for C. diversa, many ant guests have been reported (Kistner 1983;Kistner and Mcnairn 1991;Geiselhardt et al. 2007). Although there is no evidence of the biological relationship between R. lixa sp. nov. and C. diversa, this observation could be a foothold for further understanding the little-known biology of Rhadinoscelidia.