Bull. Natn. Sci. Mus., Tokyo, Ser. A, 30(4), pp. 173–179, December 22, 2004

Microdon katsurai, a New Species of Myrmecophilous Hoverfly(Diptera, Syrphidae) from Japan, Associated with Polyrhachis
lamellidens (Hymenoptera, Formicidae)
Munetoshi Maruyama1 and Teruhiko Hironaga2
1

Department of Zoology, National Science Museum,Hyakunin-chô 3–23–1, Shinjuku-ku, Tokyo, 169–0073 Japane-mail: maruyama@kahaku.go.jp
2
Systematic Entomology, Graduate School of Agriculture, Hokkaidô University,Sapporo-shi, 060–8589 Japane-mail: teruhiro@res.agr.hokudai.ac.jp

Abstract A new species of the myrmecophilous hoverfly genus Microdon (Syrphidae, Microdontinae), M. katsurai, associated with Polyrhachis lamellidens, is described in Honshû, Japan. Thisspecies is similar to M. stilboides Walker in its general appearance, but is easily distinguished by
the coloration of its body and hairs and the shape of the scutellum. The symbiotic host, P. lamellidens, has rapidly declined in population throughout Japan as a result of residential and industrial
development in its habitats. Microdon katsurai is probably an extremely rare species and will become endangered in the near future.
Key words:Introduction
Katsura (1996a) first reported the presence ofan unknown species of the myrmecophilous hoverfly genus Microdon Meigen, 1803, in Ôsaka,Honshû, Japan. It was found near a nest of
Polyrhachis lamellidens Smith, 1874 (Hymenoptera, Formicidae, Formicinae), and has attracted the attention of many Japanese dipterologists because of its large beautiful figure and brilliant green colour. After Katsura’s (1996a) report,
this hoverfly was recorded in several localities inHonshû, Japan: Tochigi-ken (Hironaga et al.,1998; Iwai, 2000, 2004); Mie-ken (Kano, 1999);
Yamaguchi-ken (Tanaka, 2002). Through thecourtesy of Messrs. D. Iwai, K. Katsura and H.
Ohishi, we have had the opportunity to examine
most of the material describing this species thathas been recorded in Japan.
Hironaga et al. (1998) observed ovipositional
behaviour of this species in a nest entrance of P.
lamellidens. The above authors (pers. comm.)
and we have not been confirmed any other ant-association with this species in the collecting
sites. Therefore, P. lamellidens could be regarded
as the only symbiotic host of this hoverfly.
In spite of eager research by many Japanese
dipterologists, only a few habitats of this hoverfly
have been found over the past eight years. The
symbiotic host, P. lamellidens, is generally restricted to lowland wet forests in warmer areas ofJapan. However, due to recent residential and industrial development, habitats of this ant species
have been rapidly decreasing throughout Japan.
The purpose of this paper is to describe thishoverfly as a new species and discuss the possibility of its endangerment, in the hope of initiating conservation efforts.
The terminology used in the present study follows McAlpine (1981).
The holotype is located in the Ôsaka Museumof Natural History, and some paratypes can befound in the National Science Museum, Tokyo,
as well as in the private collections of the authors.

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M. Maruyama and T. Hironaga

Taxonomy
Microdon katsurai sp. nov.
[Japanese name: Kenran-arinosuabu]
Microdon sp. (as Japanese name: “Ôgon-arinosuabu”):
Katsura, 1996a: 7; Katsura, 1996b: 26; Hironaga et al.,
1998: 17; Kano, 1999: 62; Iwai, 2000: 71; Iwai, 2004:16; Tanaka, 2002: 10.

Type series. Holotype: ?, Niryô, Takatsukishi, Ôsaka-fu, 22 VI 1996, K. Katsura leg.
Paratypes: 1 /, same data as holotype; 2 //,same data, but K. & T. Hirooka leg.; 1 ?, samedata, but T. Takemoto leg.; 1 ?, 2 //, same lo-cality, but 26 V 1998, K. Katsura leg.; 1 ?, samelocality, but 26 VI 2001, K. Katsura leg.; 1 ?,Tobiyama-jôshi, Takeshita-chô, Utsunomiya-shi,Tochigi-ken, 29 VI 1997, T. Hironaga leg.; 5 ??,1 /, same data, but 17–18 VI 1998, M. Maruyama leg.; 1 ?, 1 /, Shimokômagi, Môka-shi,Tochigi-ken, 27 VI 1997, T. Hironaga leg.; 1 ?,same data, but 18 VI 1998, M. Maruyama leg.; 2??, same locality, but 18 VI 1998, D. Iwai leg.;
1 /, same data, but 16 VI 1999; 1 ?, 1 /, Isezaki,Môka-shi, Tochigi-ken, 14 VI 2004, M. Maruyama leg.; 1 ?, Shimokomoriya, Môka-shi, Tochigi-ken, 14 VI 2004, M. Maruyama leg.; 1 ?,Figs. 1–4. Microdon katsurai sp. nov.—1, Male facies, dorsal view; 2, male head, anterior view; 3, female facies, dorsal view, 4, female head, anterior view.

New Myrmecophilous Hoverfly from Japan

Akiba-jinja, Kamimitani, Nabari-shi, Mie-ken,
13 VI 2004, K. Katsura leg.; 1 /, Chôjagahara,Tokuji-chô, Saba-gun, Yamaguchi-ken, 5 VI
2002, S. Tanaka leg.
Type locality. Takatsuki-shi, Ôsaka-fu, Honshû, Japan.
Distribution. Honshû (Tochigi-ken, Mie-ken,Ôsaka-fu, Yamaguchi-ken).
Symbiotic host. Polyrhachis lamellidens.
Etymology. Named in honour of Mr. Kohjiro
Katsura who discovered and recorded this newspecies for the first time.

175

Diagnosis. This species is quite distinctive
among the Japanese Microdon species in having
the pale brilliant green body and the orange yellow terminalia. As was already mentioned by
Katsura (1996b), M. katsurai is rather similar toM. stilboides Walker, 1849, known from the Indian and Indo-Chinese subregions. Our interpretation of M. stilboides is based on the redescriptions by Brunetti (1923) and Shiraki (1930), anda specimen from Taiwan (1 ?, Taihoku, VI 1925,T. Yoshida leg. (Systematic Entomology,Hokkaidô University)), which could be identified

Figs. 5, 6. Microdon katsurai sp. nov., living individuals. 5, Male, anterolateral view; 6, female, ditto.

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M. Maruyama and T. Hironagawith M. stilboides by Shiraki’s (1930) key. Microdon katsurai may be easily distinguished fromM. stilboides by the pale greenish body mainly
clothed with pale yellow hairs, the broader face
(0.43–0.47 times as wide as the head), and the
sub-trapezoidal scutellum. (In M. stilboides, thebody is darker, bluish or purplish, the thorax andabdomen are mostly clothed with black hairs, theface is narrower, about 0.4 times as wide as thehead, and the scutellum is almost rectangular.)
Description. Male (Figs. 1, 5). Body length:12.8–14.1 mm; wing length: 10.9–11.5 mm.
Coloration: Mostly pale brilliant green withyellowish reflection, somewhat variable in tint ofbasic colour; dorsal surface with gold lustre
under sunlight as in Fig. 5 (also in female: Fig.
6). Head (Fig. 2) with bluish lustre around antennal cavity and weakly so on vertex; eyes reddish
brown in fresh specimen; antennae black, slightlybrownish; arista dark brown. Thorax with lateralarea of scutum and upper part of anepisternum
with bluish lustre; anatergite pale brown withbluish lustre. Abdomen becoming yellowish posteriad, with a pair of brownish spots in anteriorarea of tergite II, terminalia orange yellow. Legs
blackish with bluish shimmer. Wings hyaline,slightly brownish; around veins black tinged;
veins dark brown; squamae yellowish white; halteres yellowish.
Head (Fig. 2) wider than mesonotum, about
2.1–2.2 times as wide as long, 1.4–1.5 times ashigh as long; frons 0.15–0.18 times as wide ashead at the narrowest part, and clothed with yellowish hairs, which are becoming black at middleof head; vertex clothed with yellow hairs; face
0.43–0.47 times as wide as head at middle level,slightly broadened ventrally, and clothed withlight yellow hairs; occiput clothed with pale yellow hairs, which are becoming whitish below occiput; genae very small, and clothed yellowish
pubescence. Eyes about 1.6 times as high as longin profile and sparsely covered with minute hairs.
Antennae (Figs. 7, 8) with scape slightly shorter
than two apical segments combined; flagellomere
I about twice as long as pedicel; arista shorter
than flagellomere I and about 0.7 times of its

length; ratio of scape, pedicel and flagellomere
I:— 2.4–2.7: 1: 1.8–2.1.
Thorax: scutum clothed with pale yellow hairs;
scutellum sub-trapezoidal, slightly shorter thanhalf width, with posterior margin truncated, bearing a lateral spine in each lateral side, andclothed with long pale-yellow hairs; anepimeronand upper areas of anepisternum and katepisternum clothed with pale yellow hairs.
Legs clothed with rather short yellowish hairs;
ventral side of each tarsus clothed with orange
hairs; fore tarsus with tarsomere I about 1.5
times as long as wide and with tarsomere IIwider than long, about 0.7 times as long as wide;
hind tarsus with tarsomere I about twice as longas wide and about as long as combined lengths oftarsomeres II–IV, and with tarsomere II about 1.4
times as long as wide.
Wings about three times as long as wide andabout 1.7 times as long as head and thorax combined; squamae with pale brown fringes.
Abdomen oval, about 1.25 times as long as
wide, much wider than thorax, widest at tergite
II, almost as long as head and thorax combined,
densely clothed with pale yellow hairs which arebecoming longer apicad; sternites moderately
densely clothed with long pale-yellow hairs; sternite IV with posterior margin truncate; cerci (Fig.
9) expanded and rounded dorsally; surstyli (Fig.
10) rather long, gently narrowed apicad, andinner side with a large, apically-round projection(Fig. 10, arrow)Female (Figs. 3, 6). Clearly different frommale in coloration of abdomen. Body length:13.6–15.3 mm; wing length: 11.5–13.3 mm.
Coloration: Abdomen with tergites IV and V
brilliant dark purple, apical half of sternite Vdarkened.
Head (Fig. 4) with frons 0.31–0.33 times aswide as head, gradually broadened forwards, andclothed with black hairs, which are becoming
pale yellow at sides of anterior half of head; face
0.43–0.44 times as wide as head at middle level.
Antennae with scape almost as long as flagellomere I; ratio of scape, pedicel and flagellomere
I:— 2.4–2.5: 1: 2.3–2.4.

New Myrmecophilous Hoverfly from Japan

177

Figs. 7–10. Microdon katsurai sp. nov.— 7, Left antenna, male, lateral view; 8, ditto, dorsal view; 9, cercus, lateral view; 10, surstylus, lateral view.

Abdomen: Tergite V with a large, inverted Vshaped depression.
Bionomics. The adults are observed in theend of May to the first week of July at the collecting sites. In most cases, they are hovering orresting, and sometime mating near the nest entrances of the host ants. On two occasions, thesenior author witnessed ovipositional behaviourof the hoverflies in the field. The hoverfly walked
around an entrance of a host nest, extended its
very long ovipositor beneath the body, and laid
eggs under bark near the nest entrance. The eggs

were usually laid as a cluster of two or threeeggs.
Possibility of Endangerment
Microdon katsurai was found rather recently(in 1996), considering that it is a very noticeable
insect, living in the lowland forests near areas ofhuman habitation. This suggests that M. katsurai
is generally a rare species, has very local distributions, and does not have a strong ability to distributions (Katsura, 1996b). Only a few habitats of

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M. Maruyama and T. Hironaga

this hoverfly have been found in Honshû over thepast eight years, despite considerable search on
the part of many Japanese dipterologists, searchthat has brought attention to its host ant,
Polyrhachis lamellidens. Incidentally, P. lamellidens has recently been declining in Honshû. For
example, in Kanagawa-ken of central Honshû,this ant species was among the most common
species in the lowlands about 20 years ago; however, only a few localities have been confirmed inrecent years (Kubota, pers. comm.). Similar situations have been observed throughout the lowland areas in the Kantô area (Maruyama, unpubl.
data), and probably also occurred in the otherlowland areas of Japan.
The habitat of Microdon katsurai andPolyrhachis lamellidens in Tochigi-ken, an areaof previously abundant habitat for M. katsurai,
has vanished. In Shimokômagi of Môka-shi,there once existed a large secondary forest inwhich an oak tree, Quercus acutissima Carruth,dominated. It constituted a very wet environment
with high groundwater levels. P. lamellidens
prefers such an environment. We confirmed
many nests of these ants, and observed more thanten individuals of M. katsurai per day during theseason of adult emergence. However, seven years
later, in 2004, almost all areas of Shimokômagi
have been exploited and transformed into residential zones. All the trees have been cut down,and no P. lamellidens and M. katsurai can befound. In other words, an ideal habitat for thesecreatures has disappeared. The surroundings ofShimokômagi contain one of the finest oak
forests in lowland Tochigi-ken. Fortunately, we
found another habitat of P. lamellidens and M.
katsurai near Shimokômagi in 2004, but the area
is very small and will be opened up for development within one or two years. Residential and industrial development has rapidly been proceeding in Tochigi-ken, especially in the lowland
areas that are suitable for such development. Inthe near future, habitats of P. lamellidens and M.
katsurai in Tochigi-ken will become seriously reduced, or ever will go extinct.
Similar development will probably occur, or isoccurring, in the other habitats of Microdon katsurai, as most secondary lowland forests are notprotected in Japan.
Microdon katsurai appears already to be extremely rare species and will become endangeredin the near future if no conservation efforts are
made. Immediate conservation measures must be
undertaken for M. katsurai and its symbiotic, P.
lamellidens.
Acknowledgements
We thank Mr. Keitaro Harusawa (Ôsaka-fu),
Mrs. Kazuko Hirooka (Ôsaka-fu), Mr. Takuto Hirooka (Ôsaka-fu), Mr. Daisuke Iwai (Saitamaken), Mr. Yasutsugu Kanô (Mie-ken), Mr. Kohjiro Katsura (Ôsaka-fu), Dr. Takato Kobayashi(Yamanashi-ken), Mr. Hisashi Ohishi (Kyôto-fu),
Mr. Seizo Okuno (Ôsaka-fu), Mr. MasahiroÔtsuki (Ôsaka-fu), Dr. Yoshiaki Nishikawa(Ôsaka-fu), Mr. Takuya Takemoto (Ôsaka-fu),
Mr. Shin’ichi Tanaka (Yamaguchi-ken) and Mr.
Kazuo Yamazaki (Ôsaka-fu) for their cooperationin the present study. We also acknowledge Dr.
Akihiko Shinohara (NSMT) for reading andcommenting on the manuscript and Mr. Masao
Kubota (Kanagawa-ken) for information ofPolyrhachis lamellidens.
This study is supported in part by a Research
Fellowship of the Japan Society for the Promotion of Science for Young Scientists (Postdoctoral Fellow) to M. M., and by a 21st Century Centre of Excellence (COE) Program on “Neo-Science of Natural History” (Program Leader: Hisatake Okada) at Hokkaidô University financed by
the Ministry of Education, Culture, Sports, Science and Technology, Japan to T. H.
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