The genus Ismarus Haliday (Hymenoptera, Ismaridae) from China

The genus Ismarus Haliday from China is revised. Six species are recognized, of which two species are described as new: Ismarus areolatus Chen, sp. nov., and Ismarus paradorsiger Chen, sp. nov. By examining the pits along the anterolateral margin of mesoscutum and comparing them with the typical notauli in Diapriidae, we conclude that the so-called reduced notauli in Ismarus are actually foveae of the mesoscutual suprahumeral sulcus. An updated key to the Chinese species of the genus is provided.


Introduction
Ismarus Haliday is the only genus in Ismaridae, with 57 described species worldwide (Masner 1976;Johnson 1992;Liu et al. 2011;Comério et al. 2016;Kolyada and Chemyreva 2016;Kim et al. 2018a, b). Available biological data suggest that species of Ismarus are hyperparasitoids of Dryinidae, which are parasitoids of Auchenorrhyncha (Hemiptera), such as leafhoppers, planthoppers and treehoppers (Chambers 1955(Chambers , 1981Nixon 1957;Wall 1967;Kozlov 1971;Masner 1976;Jervis 1979;Tussac and Tussac 1991;Olmi 2000). In addition, studies suggested species of Ismarus are likely to be found from wooded areas at higher elevations in warmer climatic zones and at low elevations in cooler climatic zones (Masner 1976;Kim et al. 2018a, b). However, only six species of Ismarus have been recorded from the Oriental regions (Liu et al. 2011;Izadizadeh et al. 2020). The Oriental fauna of Ismarus is still clearly undersampled, considering the diversity of Dryinidae (Xu et al. 2013) and preferred habitats in these regions. In the present study, we examine the species of Ismarus from China, including descriptions of two new species.

Materials and methods
This work is based upon the specimens in the following collections, with abbreviations used in the text: SCAU, Hymenoptera Collection, South China Agricultural University, Guangzhou, China; SYSBM, Sun Yat-sen University, The Museum of Biology, Guangzhou, China.
Morphological terminology otherwise follows Masner (1976). Species of Ismarus from the Oriental and Palearctic regions recently have been quite thoroughly reviewed and keyed (Liu et al. 2011;Kolyada and Chemyreva 2016;Kim et al. 2018a;Izadizadeh et al. 2020), which allow us easily identify the Chinese species in this study.
Specimens were examined using a Nikon SMZ800N microscope. Images and measurements were made using a Nikon SMZ25 microscope with a Nikon DS-Ri 2 digital camera system. Scanning electron micrographs were produced using a Phenom Pro Desktop SEM and a single montage images were generated from image stacks in the program Helicon Images were post-processed with Abobe Photoshop CS6 Extended.  Muesebeck (1972).

Remarks.
In the revision of the New World Ismarinae (then was treated as a subfamily of Diapriidae and contained the only genus, Ismarus), Masner (1976) pointed out that Ismarus "is usually characterized by the low insertion of antennae, transverse head, and the absence (better reduction) of notauli". This suggests that he was not certain about the status of notauli within the genus. However, in the key to subfamily of Diapriidae and the descriptions of the New World species, he continued to state that "notauli were always present but reduced to anterior pits". Subsequent researchers followed Masner's diagnosis of the genus and described these pits as notauli (Liu et al. 2011;Kolyada and Chemyreva 2016;Kim et al. 2018a, b), except Kolyada and Chemyreva (2016) described the anterior pits as the reduced notauli and the rest of the pits along the anterolateral margin of mesoscutum as part of the mesoscutual suprahumeral sulcus. We here examine these pits (Fig. 1A, B) using scanning electron microscopy and compare them with the notauli in a species of Coptera Say (Diapriidae), which has typical notauli (Fig. 1C). The pits in Ismarus are along the anterolateral margin of mesoscutum where the mesoscutual suprahumeral sulcus is located in many groups of Hymenoptera and are different from the pits of the typical notauli such as found in Coptera. The anterior pits in Coptera is located at the anterior margin of the longitudinal grooves of the notauli and apparently are a part of the notauli, while the pits in Ismarus (if they are present) are parallel to the anterolateral margin of the mesoscutum and never present as a part of any longitudinal grooves of the tmesoscutum. Therefore, we here conclude that the pits present along the anterolateral margin of the mesoscutum in Ismarus constitute part of the mesoscutual suprahumeral sulcus and are not notauli. The mesoscutual suprahumeral sulcus can be totally absent (as in Ismarus dorsiger (Haliday)), present as a single pit on each side (as in Ismarus halidayi Foerster, Fig. 1B), or present as a few pits of varying size (as in Ismarus nigritrochanter Liu, Chen & Xu, Fig. 1A). Mesoscutal suprahumeral sulcus present as a single anterior pit (Fig. 15C); anterior mesoscutellar pit large, longer than length of the mesoscutellar disc ( Diagnosis. This species can be easily distinguished from other Oriental species of Ismarus by the following characters: lateral pronotal area with a submedian oblique carina; mesoscutellum areolate and posterior rim excavate with slightly prominent posterolateral corners; hind tibiae abruptly incrassate. Description. Female. Body length 2.24-3.15 mm. Colour. Body black; A1-A2 brown, remainder of antenna black; coxae of fore and mid legs black, remainder brown to yellow, with tibia and tarsi becoming paler, hind leg mostly black with trochanter dark brown; wings hyaline, veins blackish brown.
Head. Head in dorsal view 2.0 × as wide as long; vertex abruptly sloping behind ocelli; POL as long as OOL; frons with ventrolateral areas densely setose, area below anterior ocellus with scattered setae; facial transverse carina slightly convex ventrally; A3 slightly longer than A4; A4 1.2 × length of A5; A6-A14 with each segment less than 1.5 × as long as wide; A15 approximately 2.0 × longer than wide.
Wings. Radial cell completely closed, very small, 4.4 × as long as wide and 0.2 × as long as marginal vein.
Legs. Fore and mid legs slender; hind tibia abruptly incrassate, its maximum width slightly wider than hind femur.

Ismarus nigritrochanter Liu, Chen & Xu
Coments. This species was originally described based on a singleton female (Liu et al. 2011).
Distribution. China (Yunnan). Ismarus paradorsiger Chen, sp. nov. http://zoobank.org/286a8f58-8922-42a1-a4f7-d23d3ff3a0e9 Figures 12-14 Diagnosis. This species is most similar to the widely distributed I. dorsiger and I. kakamegensis in size and color patterns. It can be easily separated from I. dorsiger by the presence of a mesoscutal suprahumeral sulcus, and from I. kakamegensis by A1, which is distinctly longer than the length of A3 and A4. Description. Female. Body length 1.95-2.3 mm. Colour. Body mostly pale yellowish, except mesoscutum, scutellum, metanotum, dorsal T1 and basal T2 variably dark brown; legs pale yellow, except hind tibia and basal tarsus somewhat brown; A1-A2 brown, remainder of antenna dark brown; wings hyaline or slightly infuscate medially, veins blackish brown. Head. Head in dorsal view 2.0 × as wide as long; vertex abruptly sloping behind ocelli; POL as long as OOL; frons with ventrolateral areas densely setose, area below anterior ocellus with scattered setae; facial transverse carina slightly convex ventrally; A3 slightly shorter than A4; A4 1.2× length of A5; A6-A14 with each segment approximately 2.0× longer than wide; A15 approximately 3.0× longer than wide. Mesosoma. Dorsal pronotal area rugose-punctate and setose; lateral pronotal area rugose-punctate ventrally, smooth dorsally; mesoscutum smooth and bare, convex; mesoscutal suprahumeral sulcus present as six small pits; humeral sulcus deep and finely crenulate, slightly shorter than length of tegula; mesoscutellum smooth and slightly convex, posterior rim rounded; anterior mesoscutellar pit small, 0.25 × length of the mesoscutellar disc, distinctly crenulate at bottom, median keel strong; mesopleuron smooth and bare; metapleuron rugose and covered with dense whitish long setae. Wings. Radial cell completely closed, moderately large, 3.6× as long as wide and as long as marginal vein.
Legs. Fore and mid legs slender; hind tibia abruptly incrassate, its maximum width slightly wider than hind femur.
Male. Unknown. Etymology. The name refers to the high degree of similarity with I. dorsiger and is intended to be used as a noun in apposition.