Anagrus dmitrievi sp. n. (Hymenoptera, Mymaridae), an egg parasitoid of Zyginidia eremita (Hemiptera, Cicadellidae), a pest of maize in Xinjiang, China

Abstract A new Palaearctic species of Anagrus Haliday (Hymenoptera, Mymaridae), A. (Anagrus) dmitrievi Triapitsyn & Hu, sp. n., is described, diagnosed, and illustrated from Xinjiang Uyghur Autonomous Region of China. It was reared from parasitized eggs of the leafhopper Zyginidia (Zyginidia) eremita Zachvatkin (Hemiptera, Cicadellidae) on leaves of maize. A key to the 21 named species of Anagrus known from China is provided. Zyginidia eremita is an important economic pest in Xinjiang, occurring in approximately 90% of maize fields. The phenology and life cycle of Z. eremita is summarized. Parasitism of its eggs by A. dmitrievi in maize fields was 12–75 % (average about 38 %), thus making it a rather effective natural enemy.


Introduction
The Palaearctic leafhopper Zyginidia eremita Zachvatkin (Hemiptera, Cicadellidae, Typhlocybinae), sometimes commonly called the corn three-spotted leafhopper (Yu et al. 1995), is widely distributed in Xinjiang Uyghur Autonomous Region of China. It can cause significant damage to the cultivated crops such as corn, wheat, etc. (Poaceae). The species is also known from Serbia, Ukraine, the European part of Russia, Georgia, Azerbaijan, Uzbekistan, and Kazakhstan (Dmitriev 2017). In Xinjiang, this leafhopper is an important economic pest of maize (Yu et al. 2001;Zhang et al. 2013;Qu et al. 2016). It was previously reported there as Zygina salina Mitjaev (Yu et al. 1995;Qu et al. 2000;Yu et al. 2001;Yi et al. 2013;Zhang et al. 2013;Qu et al. 2016), a synonym of Z. eremita. Like some other leafhoppers, Z. eremita was reported to be able to transmit unidentified plant viruses that cause unnamed diseases which leave spots or scorches on the leaves. It can also cause maize plants to under-produce or even kill them (Yu et al. 2001).
An unidentified species of Anagrus Haliday (Hymenoptera, Mymaridae) was collected, with numerous individuals of Z. eremita, by sweeping in maize fields in Jimsar and Mulei counties of Xinjiang (Yi et al. 2013). However, even though Yi et al. (2013) reported a positive correlation between this species [as Anagrus sp(p). and A. breviphragma Soyka] and Z. eremita [as Zygina salina], a definite host-parasitoid association between them was not established until the fourth author first reared this Anagrus sp. (Fig. 4B, C) from parasitized eggs of Z. eremita on maize leaves in 2012. Specimens of the parasitoid were then sent to the third author, who determined it as belonging to an undescribed species. Here we describe and illustrate it. A scientific name for this egg parasitoid is needed for forthcoming publications on its biological traits as well as integrated control measures against it, which may include enhancement of natural control. The presented information may also be useful for integrated pest management research in other countries of Eurasia where Z. eremita occurs in the fields of economically important poaceous crops.

Taxonomic study on the egg parasitoid
Selected specimens of both sexes of the egg parasitoid were dissected and slide-mounted in Canada balsam, examined under a Zeiss Axioskop 2 plus compound microscope, and photographed using the Auto-Montage system; the photographs were then retouched where necessary using Adobe Photoshop.
Terms used for morphological features are those of Gibson (1997). All measurements were taken from slide-mounted specimens, unless stated otherwise, and are given in micrometers (µm) as length or, for the wings, as length:width. Abbreviations used are:

F
funicle segment of the female antenna or flagellomere of the male antenna; mps multiporous plate sensillum or sensilla on the antennal flagellar segments (= longitudinal sensillum or sensilla or sensory ridge(s)).
The following collection acronyms are used: Field samples were taken every 15 days mainly in maize fields and occasionally also in wheat fields. Occurrence, population density, oviposition, and overlaps among the generations of Z. eremita were recorded, and damage to the crops by this pest was assessed. From June to September 2012, field samples were collected by sweeping with a net (200 mesh size) every five days; each time we swept for 45 minutes. Adult leafhoppers were collected by aspirator into ventilated containers supplied with maize leaves. An experimental group comprised 12-16 adult leafhoppers of the same morphospecies per container; these were then transported to the laboratory. We also searched in the field for Z. eremita eggs imbedded in maize leaves, either by a naked eye or using a portable magnifying glass; once found, the entire maize leaves with the leafhopper eggs were cut and placed into mesh bags.

CNC
Both the adult leafhoppers and nymphs were counted for statistical analysis. Maize leaves containing leafhopper eggs were divided into groups, each counted and marked under a microscope, placed in glass Petri dishes (95 mm diameter) or in glass vials (200 mm length, 40 mm diameter). The containers were kept at a suitable humidity by putting a cotton ball dipped in with pure water, and sealed by gauze in order to provide air. Then the vials were placed in an incubator with constant temperatures of either 26 °C or 30 °C and relative humidity of 35 %.
Parasitoids emerging from the parasitized leafhopper eggs were preserved in 75 % ethanol and kept in a refrigerator at +4°C until used for identification. Voucher specimens from this study (both of leafhoppers and their egg parasitoids) are deposited mainly in ICXU, while some of them were also deposited in UCRC. Non-type material examined. Numerous specimens of both sexes in ethanol, deposited in ICXU, reared by L. Yi (Yi Long) from eggs of Z. eremita during 2012 (Yi et al. 2013).
Diagnosis. Anagrus dmitrievi, sp. n. is characterized by the following unique combination of features: antenna ( Fig. 1B) with F1 slightly more than half of pedicel length, F2 longest of funicular segments, F3-F6 subequal in length and slightly shorter than F2, F4 usually without mps but sometimes with one mps (occasionally only on one antenna), F5 with one or two mps, F6 with two mps, and clava with five mps; midlobe of mesoscutum with a pair of adnotaular setae (Fig. 1D); fore wing ( Fig. 2B) 9.0-9.1 × as long as wide and its disc with several rows of setae leaving no distinct bare areas in its broadest part; ovipositor exserted beyond apex of gaster by 0.06-0.15 × total own length and 2.1-2.4 × length of protibia, each second valvifer with three distal setae ( Fig. 2A).
Description. Female (holotype and paratypes). Body length of dry-mounted, critical point-dried paratypes 400-627 µm (495 µm of the holotype; measurements taken prior to slide-mounting). Head light brown to brown except eyes and ocelli reddish; body mostly yellowish or light brown except anterior half or so of mesoscutum brown, frenum of scutellum white, and propodeum lemon yellow; scape, pedicel and F1 yellow, rest of flagellum brown; legs yellowish, wings hyaline. Antenna ( Fig. 1B) with scape 3.5-3.6 × as long as wide, with cross-ridges, 1.7-1.8 × length of pedicel; F1 cylindrical, slightly more than half of pedicel length; F2 longest of funicular segments; F3-F6 subequal in length and slightly shorter than F2; mps on F4 (usually none but sometimes one, occasionally only on one antenna as in the holotype, Fig. 1B); F5 (one or two), and F6 (two); clava with five mps, 3.0-3.3 × as long as wide, about as long as combined length of two preceding segments. Mesosoma shorter than metasoma (Fig. 1C). Midlobe of mesoscutum with a pair of adnotaular setae (Fig. 1D). Fore wing ( Fig. 2B) 9.0-9.1 × as long as wide, longest marginal seta 2.8-3.0 × maximum wing width; distal macrochaeta 2.0-2.7 × length of proximal macrochaeta; disc with several rows of setae (two such rows just beyond apex of venation, the row of setae along pos- terior margin originating behind apex of venation), leaving no distinct bare areas in its broadest part. Hind wing (Fig. 2B) 24-27 × as long as wide, longest marginal seta 6.0-6.5 × maximum wing width; disc mostly bare except for admarginal rows of setae. Ovipositor anteriorly not extending to mesophragma in slide-mounted specimens and posteriorly exserted beyond apex of gaster by 0.06-0.15 × total ovipositor length. Second valvifers (= external plates of ovipositor of authors) (Chiappini 1989;Chiappini et al. 1996;etc.) each with three distal setae ( Fig. 2A)  Male (paratypes). Body length of the dry-mounted, critical point-dried paratypes (including prior to slide-mounting) 462-594 µm. Similar to female except for the normal sexually dimorphic features such as antenna (Fig. 3A) and genitalia (Fig. 3C), and the following. Body somewhat darker than in female, particularly gaster light brown to brown; fore wing ( Fig. 3B) 7.3-8.2 × as long as wide.
Remarks. The new species belongs to the incarnatus species group of the nominate subgenus of Anagrus, as defined by Chiappini et al. (1996), in whose key it runs to A. flaveolus Waterhouse (see below). In Chiappini and Lin (1998), A. dmitrievi keys in the same couplet together with A. striatus Chiappini & Lin, a completely different species whose female has one mps on F3 and a bare area on the broadest part of the fore wing disc. In Triapitsyn and Berezovskiy (2004), A. dmitrievi keys to A. nigriceps (Smits van Burgst) in which an mps is present on F3 of the female antenna (Chiappini et al. 1996) whereas it is always absent on that segment in A. dmitrievi.
When, as usually, F4 of the female antenna of A. dmitrievi lacks an mps, it is most similar to the Nearctic species A. sophiae S. Trjapitzin, which, however, has a relatively much longer ovipositor (2.7-3.8 × length of protibia) (Trjapitzin and Strong 1995). When F4 of the female antenna bears an mps (at least on one antenna), it is most similar to the New World species A. flaveolus, from which it differs in F5 being about as long as F4 and F6 and also in having the row of setae along the posterior margin and originating behind the apex of venation of the fore wing (whereas in A. flaveolus, F5 is always shorter than F4 and F6, even when an mps is present, and the row of setae along the posterior margin of the fore wing does not extend to apex of venation). Those females of A. dmitrievi that bear an mps on F4 on both antennae are also somewhat similar to females of the Palaearctic species A. brocheri Schulz, whose general body color is much darker (dark brown).
In the world key to the species of Anagrus by Triapitsyn (2015), females of A. dmitrievi key either to A. sophiae (when an mps is present on F4) or A. flaveolus (when an mps is absent on F4).
The updated key to the Chinese species of Anagrus (below) was modified from Triapitsyn (2015). The previous key (Chiappini & Lin 1998)  Host. The parasitoids of the type series were definitely reared from eggs of Zyginidia eremita because we also reared this leafhopper from its unparasitized eggs during the same collecting event; these leafhoppers were later compared with the positively identified specimens.
Biology and parasitism. Leafhopper's eggs parasitized by A. dmitrievi turn dark reddish (Fig. 4A). The optimal constant incubation temperature under laboratory conditions for immature A. dmitrievi was 25 °C, at which about 38 % of the eggs hatched. Estimated field parasitism rate of Z. eremita eggs by A. dmitrievi in Xinjiang was 12-75 % (average about 38 %), thus making it a rather effective natural enemy. Ovipositor projecting beyond apex of gaster by approx. 1/3 of its total length; ovipositor: protibia ratio at least 3. Fore wing disc with hairless area occupying its whole posterior half; fore wing length: width ratio more than 10.

Identification of the host leafhopper
The corn three-spotted leafhopper, collected on 7.viii.2012 by J. Lu (Lu Jiaxiong) and L. Yi (Yi Long) on maize plants at the same locality as the type series of A. dmitrievi, were identified by Dmitry A. Dmitriev as Zyginidia (Zyginidia) eremita (voucher specimens in INHS and additional 2 females in UCRC). This was the most abundant leafhopper species feeding on maize plants in Anningqu. Another rather common leafhopper on maize in Xinjiang was Cicadella viridis (Linnaeus) (Yi et al. 2013). Adult Z. eremita ( Fig. 5H-J) have a characteristic grayish white color; light brown markings decorate the costal margin of vertex. The pronotum is transparent, and three equal-sized oval black spots are present on the adults' mesoscutum. The fore and hind wings are crystal white, and the abdomen has black, transverse, dorsal bands. The average length of adult Z. eremita is 2.6-2.8 mm.

Records, phenology, and life cycle of Z. eremita
Zyginidia eremita has quite frequent records in Xinjiang (Fig. 6). It occurred in almost every maize field sampled. Only 5-10 % of the maize fields had a relatively sparse population of Z. eremita. The highest population densities observed were in Jimsar, Qitai, Mulei, Changji, and Urumqi.
In Xinjiang (eastern Xinjiang: Jimsar, Qitai, Mulei, Balikun, and Hami; northcentral Xinjiang: Ili, Turpan, Korla, and Urumqi (Anningqu)), Z. eremita has three generations per year and these overlap during the warm months. According to Yu et al. (1995), adult leafhoppers of this species overwinter in winter wheat or in poaceous weeds. But according to Yu et al. (2001), adults also overwinter in surrounding trees, although no details exactly where they hide were provided by these authors.  Adult leafhoppers start to emerge from their overwintering shelters in late April; in about mid-May, at least some of them apparently move to winter and spring wheat (Yu et al. 1995). The first generation of nymphs appears on wheat plants in late May. In early June, the first generation of adult leafhoppers migrates to maize fields and feeds on the seedlings. Their peak oviposition period occurs in late June. The leafhopper species collected by J. Lu on 13.vi.2014 in the wheat field in Anningqu was, however, not Z. eremita but Macrosteles (Macrosteles) alpinus (Zetterstedt) [2 females and 2 males in UCRC, determined by D. A. Dmitriev].
Females of Z. eremita prefer relatively mature leaves of maize plants for oviposition. Most eggs are laid in the leaves near the ground, very rarely in the upper leaves on a plant. Transparent oval eggs of the corn three-spotted leafhopper are usually laid into the leaf tissue near the bottom of a leaf close to the middle vein.
In early July, the second generation of nymphs hatches, and within about ten days their population density becomes very high. The second generation of adults oviposits in maize leaves in late July and early August. Peak abundance of the third generation nymphs is in mid to late August. Adult leafhoppers of the third generation gradually move in the fall to winter wheat (Yu et al. 1995) or grass (Yu et al. 2001).
Life history and phenology of Z. eremita are summarized in Table 1, and its life cycle is shown in Fig. 5.

Discussion
The only other available records of egg parasitoids of Zyginidia spp. are those of Anagrus atomus (Linnaeus) from Z. (Zyginidia) pullula (Boheman) on maize in Italy (Vidano and Arzone 1988), from Z. (Zyginidia) scutellaris (Herrich-Schäffer) on maize in France (della Giustina and Caruhel 1989), and from Z. sohrab Zachvatkin on maize in Turkey (Mutlu and Sertkaya 2015), as well as of Lymaenon litoralis (Haliday) (Mymaridae) from Z. sohrab on wheat in Iran (Fallahzadeh and Huber 2011). Baquero and Jordana (1999) reported that large numbers of A. atomus, an egg parasitoid of Z. scutellaris, were captured in Navarre, Spain, where it is the most abundant leafhopper in maize fields.