Descriptions of two new species of Platygaster Latreille that attack gall midges (Diptera, Cecidomyiidae) with notes on their biology (Hymenoptera, Platygastridae)

Abstract Platygaster ingeniosus Matsuo & Yamagishi, sp. n. and P. urniphila Matsuo & Yamagishi, sp. n. (Hymenoptera: Platygastridae) are described from Japan. The former species is an egg-larval solitary parasitoid of Masakimyia pustulae Yukawa and Sunose (Diptera: Cecidomyiidae). The latter species is an egg-larval gregarious parasitoid of Rhopalomyia longitubifex (Shinji) (Diptera: Cecidomyiidae).

As demonstrated by Askew (1975) for parasitoids of Cynipidae (Hymenoptera), Yukawa et al. (1981) also divided parasitoids of gall-inducing cecidomyiids (Diptera: Cecidomyiidae) into two groups, early and late attackers, according to their parasitic strategies. Early attackers (koinobionts) are host-specific endoparasitoids that oviposit into host eggs or younger host larvae before galls start to develop (Sunose 1984(Sunose , 1985aTabuchi and Amano 2004). In contrast, late attackers (idiobionts) are polyphagous ectoparasitoids attacking final (third) instars or pupae. Species of Platygaster that are associated with gallinducing cecidomyiids are known as typical early attackers (Askew 1975). Host specificity has been paid special attention in behavioral and ecological studies of Platygaster, particularly host-parasitoid interactions. For example, Stireman III et al. (2006) demonstrated host-associated genetic differentiation in Platygaster variabilis Fouts that attacks Rhopalomyia solidaginis (Loew) (Diptera: Cecidomyiidae). Yamagishi (1980) reported that larvae of Rabdophaga rosaeformis Kovalev (Diptera: Cecidomyiidae) parasitized by Platygaster stimulator Yamagishi mature in summer whereas unparasitized R. rosaeformis larvae pass through the summer as first instars. In terms of reproductive strategy, some species including P. robiniae Buhl and Duso are known to be gregarious parasitoids (Kim et al. 2011). In addition, polyembryony, the production of genetically identical embryos from a single egg through clonal division, has been found in several species of Platygaster such as P. feltii Fouts, and P. vernalis (Myers) (Leiby and Hill 1924;Segoli et al. 2010).
In order to contribute to further taxonomic and ecological studies of platygastrid parasitoids, we intend in this paper to identify the two undescribed species of Platygaster and to provide information on their host range and reproductive strategies.

Materials and methods
Galls of Masakimyia pustulae and Rhopalomyia longitubifex were collected from Kyushu, Japan, in 2007-2017 to rear sufficient numbers of adults of Platygaster species for taxonomic study. In rearing Platygaster species that attacks Rhopalomyia longitubifex, the number of males and females emerged from one host larva were recorded to confirm its gregarious parasitism.
For morphological observation, adult parasitoids were preserved in 70-75% ethanol and subsequently dried from ethanol using the method described in Matsuo and Yukawa (2009). Specimens were observed under a binocular microscope (LEICA S8APO). Several specimens were gold-coated for microphotography with a JEOL JSM-5600LV scanning electronic microscope. High-resolution bright field images were taken with LEICA S8APO and CANON EOS D600 (Matsuo et al. 2012).
To compare morphological characters between known and the two Japanese species, we referred to original descriptions, redescriptions or keys for 512 (85.2%) out of 601 known species (Suppl. material 1). Unfortunately, we could not obtain adequate morphological information on the remaining 89 species. In addition to literature survey, we examined high-resolution images of the type specimen of a Japanese species, Platygaster gifuensis (Ashmead) that has been kept in the Smithsonian National Museum of Natural History, Washington, DC, USA. Adult morphological terminology follows Masner and Huggert (1989), except for head and mesosoma, which follows Mikó et al. (2007).
Holotypes and paratypes of the new species are deposited in the collection of the Biosystematics Laboratory, Faculty of Social and Cultural Studies, Kyushu University, Fukuoka, Japan.

Taxonomy
Morphological comparison with some congeners revealed that the two unidentified species of Platygaster are distinct species and new to science. They are described below as P. ingeniosus and P. urniphila. The two new species share typical morphological characteristics of Platygaster and are distinctly different from the exceptional species mentioned in the Introduction.
Metasoma as long as head and mesosoma combined; T1 evenly crenulated, 1.8-1.9 times as wide as long, 0.2-0.3 times as long as T2; T2-T5 with a band of shallow punctation along posterior margin; T2 weakly striated in basal half, with shorter striae medially (Fig. 9); T3 with a few setae; T4 with a row of setae which is broken medially; T5 with a complete setal row; T6 with a complete setal row, smooth.
MALE. Differs from the female as follows: Body length 1.5-1.6 mm. Antenna with erect setae; A4 distinctly widened (Fig. 5). Metasoma approximately 0.8 times as long as head and mesosoma combined, obtuse at apex. Differential dagnosis. Platygaster ingeniosus is similar to the two Palearctic species, P. rutilipes Buhl and P. yunnanensis Buhl, because they share the following morphological characteristics: notaulus indicated in posterior half; mesopleuron with a coriaceous area below tegula; posterior margin of mesoscutum reaching base of mesoscutellum; hind wing approximately 4.8 times as long as wide. Platygaster ingeniosus can be distinguished from P. rutilipes by having the stouter fore wing that is 2.3-2.4 times as long as wide whereas P. rutilipes has elongated fore wing, approximately 2.8 times as long as wide. Platygaster ingeniosus could be distinguished from P. yunnanensis because sides of pronotum are finely reticulate whereas smooth in P. yunnanensis.
Mesosoma as high as wide, 1.3-1.4 times as long as wide; sides of pronotum broadly smooth which is sometimes with extremely fine striae, smooth along posterior margin (Fig. 15); mesoscutum smooth in posterior half; notauli indicated in posterior half (Fig. 16); posterior margin of median lobe of mesoscutum not reaching base of mesoscutellum, with numerous long setae laterally; scuto-scutellar groove smooth and bare; mesoscutellum distinctly convex, smooth and covered with long hairs except median glabrous area (Fig. 17); mesopleuron with two setae anteriorly, with a coriaceous area below tegula; mesopleural carina absent; mesofurcal pit present; metapleuron pilose, sparse in dorsal one-third; propodeal carinae widely separated, parallel. Fore wing approximately 2.4 times as long as wide; marginal cilia approximately 0.1 times as long as width of fore wing. Hind wing approximately 5.3 times as long as wide, with two hamuli; marginal cilia approximately 0.2 times as long as width of hind wing.
Metasoma as long as head and mesosoma combined; T1 evenly crenulated, 1.7-1.8 times as wide as long, 0.2-0.3 times as long as T2; anterior margin of T2 weakly produced and overlapped T1; T2 weakly striated in basal half, with shorter striae medially (Fig. 18); T2-T5 with a band of shallow punctuation along posterior margin; T3-T5 with a row of setae which is broken medially; T6 with a setal row which is sometimes sparse medially, smooth.
MALE. Differs from the female as follows: Body length 1.1 mm. Antenna with erect setae; A4 distinctly widened; A5-A9 quadrate (Fig. 14). Metasoma approximately 0.8 times as long as head and mesosoma combined, obtuse at apex. Differential diagnosis. Platygaster urniphila can be distinguished from P. urnicola Yamagishi, a Japanese species, based on the following characteristics: mesopleuron with a few setae anteriorly (glabrous in P. urnicola); posterior margin of median lobe of mesoscutum not reaching base of mesoscutellum (reaching base of mesoscutellum in P. urnicola). Platygaster gifuensis was described based on a single male from Japan, from which P. urniphila can be distinguished by having A5-A9 quadrate (approximately 1.5 times as long as wide in P. gifuensis). Platygaster urniphila is quite similar to P. sublongicornis Buhl because they share the following morphological characteristics: vertex between ocelli smooth; frons smooth medially; mesopleuron with a few setae anteriorly, with a coriaceous area below tegula; mesoscutellum distinctly convex; T2 weakly striated in basal half, with shorter striae medially. However, Platygaster urniphila can be distinguished from P. sublongicornis based on the following characters: A4-A5 subquadrate (distinctly elongate in P. sublongicornis); OOL as long as LOL (1.6 times as  long as LOL in P. sublongicornis); sides of pronotum smooth along posterior margin (smooth along anterior and posterior margins in P. sublongicornis); hind wing approximately 5.3 times as long as wide (4.5 times in P. sublongicornis). Biological notes. Platygaster urniphila is an egg-larval gregarious parasitoid of Rhopalomyia longitubifex that induces axillary bud galls on Artemisia indica var. maximowiczii in Japan (Yukawa and Masuda 1996;Ganaha et al. 2007). Gall polymorphism has been found in R. longitubifex: long jar-shaped, jar-shaped, and globular jar-shaped (see figures 1-5 of Ganaha et al. 2007). At present, P. urniphila has been reared only from globular jar-shaped galls. Various sorts of galls induced by Rhopalomyia spp. have been found on Artemisia spp. (e.g. Yukawa and Masuda 1996;Yukawa 2014; Gagné and Jaschhof 2017), but P. urniphila has been reared only from galls of Rhopalomyia longitubifex on A. indica var. maximowiczii in Japan. Future intensive studies are needed to confirm the host range of P. urniphila. Leiby and Hill (1924) noted that Platygaster vernalis, a polyembryonic species, occasionally laid male and female eggs into a single host egg. Thus, P. vernalis has both polyembryonic and gregarious reproductive strategies. Our rearing experiments indicated that P. urniphila is a gregarious parasitoid because males and females were reared from a single host larva (Table 1). To confirm polyembryonic reproduction by P. urniphila, we need histological survey or MIG-seq analysis (Suyama and Matsuki 2015) that discriminate individuals originated from clonal division and sexual reproduction. mutualism), Ministry of Education, Culture, Sports, Science and Technology, Japan to KM and the Academic Challenge 2010 from Robert T. Huang Entrepreneurship Center of Kyushu University, Japan to TF.