Description of a new species of Aphanogmus Thomson (Hymenoptera, Ceraphronidae) that parasitizes acarivorous gall midges of Feltiella (Diptera, Cecidomyiidae) in Japan

Abstract In 2008–2009, we reared small ceraphronids (about 0.5 mm in body length) from cocoons that had been made possibly by two acarivorous species, Feltiella acarisuga (Vallot) and Feltiella acarivora (Zehntner) (Diptera: Cecidomyiidae) in Okinawa, Japan. Detailed morphological observation revealed that the ceraphronid was a new species of Aphanogmus Thomson (Hymenoptera: Ceraphronidae). We describe it as Aphanogmus flavigastris Matsuo, sp. n. Identification of the Aphanogmus species is essential to evaluate its possibly negative effects on the predatory activity of Feltiella species that have been used as control agents against tetranychid mites.

A few taxonomic studies have focused on Japanese species of Aphanogmus. Ashmead (1904) first recorded Aphanogmus from Japan, describing A. hakonensis Ashmead based on individuals collected from Hakone, Kanagawa. Polaszak and Dessart (1996) detected several cryptic species of Aphanogmus hakonensis and proposed the species complex of A. hakonensis. Ishii (1937) reported an unidentified species of Aphanogmus as a parasitoid of Cybocephalus species (Coleoptera: Cybocephalidae) that feed on Unaspis yanonensis (Kuwana) (Hemiptera: Diaspididae) on citrus in Japan. Evans et al. (2005) considered that Aphanogmus sp. reported in Ishii (1937) was identical to A. inamicus Evans and Dessart. In total, two nominal species, Aphanogmus hakonensis and A. inamicus have been known in Japan.
Larvae of all known Feltiella species feed on tetranychid mites (Acari: Tetranychidae) (Gagné 1995, Gagné andJaschhof 2014). In particular, Feltiella acarisuga is regarded as an important natural enemy against tetranychid mites that frequently develop pesticide resistance and cause serious damage to various agricultural products (Barnes 1933, Wardlow andTobin 1990). Therefore, the purpose of this study is to identify the Aphanogmus found in Okinawa, as this is essential to evaluate its effect on mortality of Feltiella species.

Material and methods
We collected more than one larva or cocoon of Feltiella from each collecting site in Okinawa, Japan in 2008-2009. They were kept in petri-dishes to rear Aphanogmus and Feltiella species. Adults that emerged were preserved in 75% ethanol for morphological observation. If possible, host species of parasitoid wasp should be identified by examining remnants of host insect but the male genitalia of host cecidomyiid, which is important for species identification, would not be included in the remnants. Otherwise, host species should be identified before the attack of parasitoid wasps. However, this is not always applicable under natural conditions. Therefore, we regarded host cecidomyiid to be identical to either F. acarisuga or F. acarivora when A. flavigastris emerged from cocoons that coexisted on the same plant with either F. acarisuga or F. acarivora, respectively because we have seldom seen F. acarisuga and F. acarivora on the same plant.
For microscopic study, the ethanol-stored specimens were dried by the method described in Matsuo and Yukawa (2009). Fore wings were mounted on slides in Canada balsam using ethanol and xylene. Several specimens were gold-coated for microphotography with a JEOL JSM-5600LV scanning electronic microscope. High resolution image was taken with the methods described in Matsuo et al. (2012). Adult morphological terminology follows Mikó and Deans (2009), except for wing venation, which follows Dessart (1963). The holotype and paratypes are deposited in the collection of the Biosystematics Laboratory, Faculty of Social and Cultural Studies, Kyushu University, Japan. Etymology. The specific name, flavigastris, is Latin meaning yellowish gaster, derived from the color of the female metasoma.
Fore wing about 3.0 times as long as wide, with a darkly pigmented band (Fig. 8); radial vein 1.4-1.5 times as long as marginal vein. Metacoxa bare dorsally; longitudinal metacoxal carina present at base. Syntergum with distinct transverse carina anteriorly, smooth, with 2-3 setae anterolaterally, occupying more than half of total length of metasoma; longitudinal striae of syntergum absent.
Distribution. Japan. Host insects. Feltiella acarisuga and F. acarivora. Usually one, occasionally two or three adults emerged from a single host cocoon. Evans et al. (2005) proposed the following three species groups based on characteristics of the mesosoma and metasoma:
According to the morphological features of these species groups, the new species belongs to the fumipennis group, while Aphanogmus fulmeki and A. floridanus that have been known as parasitoids of Feltiella species belong to the clavicornis group and tenuicornis group, respectively. Therefore, the new species can be distinguished from Aphanogmus fulmeki and A. floridanus.
Among members of the fumipennis group, the new species shares the following characteristics with species in the Aphanogmus hakonensis complex sensu Polaszak and Dessart (1996): median mesoscutal sulcus present; dorsal axillar area and mesoscutellum with distinct lateral carina; syntergum with distinct transverse carina anteriorly. However, Aphanogmus flavigastris does not belong to the A. hakonensis complex based on the following characters: fore wing with a darkly pigmented band (hyaline in A. hakonensis complex); antenna of female with flagellomere 2-7 not transverse (transverse in A. hakonensis complex).
The new species is most similar to Aphanogmus inamicus as it shares the following characters: median mesoscutal sulcus present; dorsal axillar area and mesoscutellum with distinct lateral carina; syntergum with distinct transverse carina anteriorly; fore wing with a darkly pigmented band; antenna of female with flagellomere 2-7 not transverse. However, Aphanogmus flavigastris can be distinguished from A. inamicus by the following characters: club of antenna 1 segmented (3 segmented in A. inamicus); lateral carina on dorsal axillar area and mesoscutellum more raised than that of A. inamicus; longitudinal striae of syntergum absent (present in A. inamicus); mesosoma dark brown (reddish yellow in A. inamicus); infuscate area on fore wing smaller (from marginal vein to posterior margin of fore wing in A. inamicus).
According to a key to the Palaearctic species of Aphanogmus (Szelényi 1940), the new species runs to A. fasciolatus Förster based on the following characters: antenna clavate; club 1 segmented and longer than the preceding two segments combined; ra-dial vein longer than marginal vein. However, the new species could be distinguished from Aphanogmus fasciolatus by having longer pedicel that is distinctly longer than flagellomere 1 while A. fasciolatus has the pedicel that is shorter than flagellomere 1.
We need to monitor the seasonal abundance of Aphanogmus flavigastris for the successful application of Feltiella species, because its congener A. floridanus that attacks F. acarivora has been regarded to act as a negative force in controlling Tetranychus urticae Koch (Acari: Tetranychidae) on strawberry in California (Oatman 1985). Shimoda et al. (2016) recently developed a remarkable system for trapping Feltiella species and other predators of spider mites using pots of Brassica rapa Linnaeus var. perviridis L.H.Bailey (Brassicaceae), 'komatsuna' in Japanese, which bore Tetranychus urticae. They could rear an unidentified species of Aphanogmus from Feltiella acarisuga with the trapping system. This method may be useful to collect plenty of individuals of Feltiella and its parasitoids from 'komatsuna' in the fields. Further field surveys are needed to verify the efficacy of this method as a monitoring tool for Aphanogmus flavigastris.