Bull. Natl. Mus. Nat. Sci., Ser. B, 39(1), pp. 21–24, February 22, 2013

Pollinators of Arisaema thunbergii subsp. urashima (Araceae) in Japan
Norio Tanaka1,*, Mitsuhiro Sasakawa2 and Jin Murata3
1

Department of Botany, National Museum of Nature and Science,
Amakubo 4–1–1, Tsukuba, Ibaraki 305–0005, Japan
2
Korigaoka 7–6–7, Hirakata, Osaka 573–0084, Japan
3
Botanical Gardens, Graduate School of Science, The University of Tokyo,
Hakusan 3–7–1, Bunkyo-ku, Tokyo 112–0001, Japan* E-mail: ntanaka@kahaku.go.jp(Received 16 November 2012; accepted 19 December 2012)

Abstract Pollinators of Arisaema thunbergii subsp. urashima (Araceae) were investigated at twosites in Japan. From inside 33 spathes, 109 insects were collected and identiﬁed to 17 families and27 genera. Sixty-six percent were fungus gnats comprising Keroplatidae, Mycetophilidae, andSciaridae. Although Arisaema has always been thought to be pollinated by fungus gnats, someother species of Diptera were shown to visit spathes of A. thunbergii subsp. urashima and are presumed to carry their pollen grains to female spathes.
Key words :Arisaema thunbergii subsp. urashima, Diptera, fungus gnat, pollination, pollinator.

Introduction
The genus Arisaema (Araceae), consisting ofca. 180 species, is primarily distributed fromeastern Africa to southeast Asia. Other three species occur from northeast North America south to
Mexico (Murata, 2011). Many species of thegenus produce male and female inﬂorescences
successively from the same plant at different seasons, depending on the size of the plant (Schaffner, 1922; Maekawa, 1924; Takasu, 1987).
The pollination mechanism is well documented. Pollinators enter the spathe tube, holding
on to the inﬂorescence by the upper mouth of thetube. After entering, the pollinators cannot
escape from the mouth because wax particles
cover both the inner wall of the tube and the surface of the spadix appendage (van der Pijl, 1953;
Vogel and Martens, 2000). In the male spathe,pollinators can escape through the exit holelocated in the lower part of the spathe. In contrast, female spathes lack an exit hole and trap
pollinators.

Fungus gnats have been reported to be pollinators of several Arisaema spp. i.e. A. negishii
Makino, A. serratum (Thunb.) Schott, and A.
yamatense (Nakai) Nakai from Japan (Sasakawa,1993, 1994a, 1994b), and A. consanguineum
Schott, A. costatum Mart., A. grifﬁthii Schott, A.
jaquemontii Blume, A. nepenthoides Mart, A.
speciosum (Wall.) Mart., A. tortuosum (Wall.)
Schott, and A. utile Hook. f. ex. Engl. from
Nepal (Vogel and Martens, 2000).
A species endemic to Japan, A. thunbergii
Blume subsp. urashima (H. Hara) H. Ohashi & J.
Murata, is characterized by a spadix appendage
with a long ﬂagellate thread. The pollinators ofthe species have never been reported. In thisstudy, we observed which species of insects visited the spathe tube of A. thunbergii subsp.
urashima.
Study sites and Methods
Pollinators of A. thunbergii subsp. urashima
were observed at two sites (Fig. 1A): 1) Bando:

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Norio Tanaka et al.

Fig. 1. Arisaema thunbergii subsp. urashima in Shimoda, Shizuoka Prefecture, Japan. A. An individual with aninﬂorescence. B. Exit hole (arrow) of male spathe. C. Insects (arrows) trapped around the bottom of spathe ofthe species.

Koizumi, Bando, Ibaraki Pref. Japan. Plants
grow in the ﬂoor of the temperate deciduous
broad-leaved forest, where Quercus serrata var.
serrata Murray (Fagaceae) dominates. 2) Shimoda: Ebisu-Jima, Suzaki, Shimoda, Shizuoka
Pref., Japan. Plants grow in the ﬂoor of the laurel
forest that consists mainly of Camellia japonica
L. (Theaceae) and Podocarpus macrophyllus(Thunb.) Sweet.
At the Bando site, collection of pollinators wascarried out between April 8 and April 25, 2005.
To collect insects visiting the spathe tubes of A.
thunbergii subsp. urashima, the exit holes in thelower part of male spathes were plugged withcotton wool (Fig. 1B). A week later, the insects
inside the spathes were collected. At the Shimoda
site, collection was conducted on April 14, 2005,

without plugging the exit holes of the malespathes.
Results and Discussion
Insects were found inside of 14 (seven maleand seven female spathes) of 45 spathes at theBando site and 19 (ﬁve male and 14 femalespathes) of 73 spathes at the Shimoda site (Fig.
1C). From the 33 spathes, 109 individual insects
were collected. All were identiﬁed as Diptera,with the exception of one individual from theOrder Thysanoptera. The insects were classiﬁed
into 17 families and 27 genera. Seventeen species
were clearly identiﬁed (Table 1).
Of the collected insects, 66% (72/109 individuals) were fungus gnats, comprising Keroplati-

Pollinators of Arisaema thunbergii subsp. urashima (Araceae) in Japandae, Mycetophilidae, and Sciaridae. Although
Arisaema has always been thought to be pollinated by fungus gnats (Sasakawa, 1993, 1994a,

231994b; Vogel and Martens, 2000), Diptera species other than fungus gnats were found insidespathes in this study. Vogel and Martens (2000)

Table 1. Diptera species collected in spathes of Arisaema thunbergii subsp. urashima in this study
Number of individuals*1FamilySpecies

Bando♂

Bibionidae
Cecidomyiidae

Bibio sp.
Cecidomyiidae gen.

Chironomidae

Chironomus sp.

Chloropidae

Cadrema minor (Meijere, 1908)

Coenomyiidae

Coenomyiidae gen.

Drosophilidae

Mycodrosophila poecilogastra Loew, 1874

Fanniidae

Fannia edentula Nishida, 1973

Keroplatidae

Neoplatyura kunashiriensis Zaitzev, 1994

Lauxaniidae

Minettia longipennis (Fabricius, 1794)

Muscidae

Muscidae gen.

MycetophilidaeAnatella sp.

♀

Shimoda?

♂

♀

Total?
1
4*20, 13, 10, 10, 1

10, 1
1, 00, 1

120, 12, 0

21, 03, 5

113

3, 0

10, 1
1, 0

1
11, 0

4

Boletina dispecta Dziedzicki, 1885

3, 0

Boletina nitida Grzegorzek, 1855

1, 0

1

Brevicornu sp.

1, 0

1

Exechia sp.

1, 01, 00, 1

Leia winthemi Lehmann, 1822

0, 1

10, 1

Mycetophila abbreviata Landrock, 1914

3*2
20, 2

Mycetophila luctuosa Meigen, 1830

1, 01

Mycetophila perpauca Lastovka, 1972

0, 1

1

Mycetophila ruﬁcollis Meigen, 1818

1, 0

1

Mycetophila sp. (type 1)

4, 2

6

Mycetophila sp.

1, 00, 1

3*20, 1

Rymosia sp.

1, 0

1

Trichonta sp.

0, 1

1

PhoridaeMegaselia sp.

2, 0

Psychodidae

Psychoda itoco Tokunaga & Etsuko, 1954

1, 0

Sciaridae

Sciaridae gen.

0, 1

1, 0

12, 1

1, 1

Bradysia trispinifera Mohrig & Krivosheina, 1979

0, 10, 1Ctenosciara insolita Sasakawa, 1994

2, 0

9, 10, 10, 1

Tephritidae
Tipulidae

Paragastrostzona japonica ShirakiLimonia sp.

9*20, 1

23*210, 92

Phytosciara sp.
Allognosta vagans (Loew, 1873)

0, 20, 1

Bradysia sp.

Stratiomyidae

7*20, 40, 7

10, 1

11, 0

*1 Left number shows number of insects found in male spathe and right one in female spathe.
*2 Number of species included is unknown.

7*20, 11

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Norio Tanaka et al.

stated that other kinds of insects will occassionally be captured and may even confer pollination; most, however, are able to escape prematurely using the “wrong” exit or lack theappropriate size and mobility to achieve pollination. In this study, insects were collected frominside spathes and most of the insects were foundat the bottoms of spathes. This indicates thatsome insects other than fungus gnats cannot
escape from the “wrong” exit. Most of the collected insects had pollen grains attached to them,and can therefore be considered to be valid pollinators in terms of attachment of pollen grains tobody.
Fungus gnats (ca. 1 mm in width) can passthrough the exit hole (ca. 2 mm internal diameter)of the male spathe. Fannia edentula (Fannidae),whose width is ca. 2 mm and larger than the othercollected species, is presumed to not be able toescape from the spathe through the hole. F. edentula were only found in the male spathes at theShimoda site, where the exit holes had not been
plugged with cotton wool (Table 1). This result
indicates that F. edentula cannot escape throughthe exit holes of the male spathes; it therefore
cannot transport pollen grains out of the malespathes and cannot contribute to pollination. By
contrast, the most other small insects were notcollected in male spathes of Shimoda site (Table1), where we had not plugged the exit hole. This
indicates that the holes of male spathes of the A.
thunbergii subsp. urashima play a role of pollinatorʼs exit from the trap.
From the female spathes, 19 individual insects
were collected from the 7 spathes (2.7 individuals/spathe) at the Bando site and 42 individuals
from the 14 spathes (3.0) at the Shimoda site.
Nishizawa et al. (2005) used microsatellite DNA
analysis to show that the seeds in a fruit had been
fertilized by multiple male parents. The visits ofmultiple insects to a spathe observed in this study
support the molecular genetic data.
Some pollinators were found at only one of thetwo sites. Chironomidae, Drosophilidae, Keroplatidae, Psychodidae, and Tephritidae were col-lected only at the Bando site. In contrast, Bibionidae, Chloropidae, Coenomyiidae, Lauxaniidae,Muscidae, Stratiomyidae, and Tipulidae wereonly at the Shimoda site. However, the sample
size in this study were too small to permit discussion of the differences between the two sites.
Acknowledgments
The authors thank Kazuo Obata and Sadamu
Matsumoto for providing information about
study sites.
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