7Proc. Arthropod. Embryol. Soc. Jpn. 49, 7 (2016)Ⓒ 2016 Arthropodan Embryological Society of Japan
ISSN 1341–1527

Early Embryonic Development of Reticulitermes speratus (Kolbe,1885) (Insecta: Isoptera, Rhinotermitidae)*Michiyo MATSUSHIMA1, 3) and Ryuichiro MACHIDA2, 3)
Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305–8572, Japan
Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305–8572, Japan
3)
Current address: Sugadaira Montane Research Center, University of Tsukuba, Sugadaira Kogen, Ueda, Nagano 386–2204, Japan
E-mail: machida@sugadaira.tsukuba.ac.jp (RM)
1)
2)

Polyneoptera are composed of 11 “orthopteroid” orders.
In contrast to many open questions about polyneopteraninterordinal relationships, the monophyly of Dictyoptera
comprising Isoptera, “Blattaria” and Mantodea is widelyaccepted. Recent phylogenetic works based on morphologicaland molecular evidence suggest Isoptera to nest in “Blattaria”.
The monophyly of Isoptera and “Blattaria”, of whichassemblage is called “Blattodea”, is well supported, but thephylogenetic position of Isoptera within Blattodea is variously
argued as well as the affinities of each blattarian lineage. Thus,
we have started an embryological study of Isoptera, using
Reticulitermes speratus (Kolbe, 1885) as materials, toreconstruct the groundplan of Isoptera and discuss its affinity
with other dictyopteran lineages from the comparativeembryological standpoint.
Colonies of Reticulitermes speratus were collected in
Sugadaira (Ueda, Nagano, Japan) and main campus ofUniversity of Tsukuba, (Tsukuba, Ibaraki, Japan), and thosecollected in Otani-ike (Iyo, Ehime, Japan) were kindly
provided by Dr. Makiko Fukui of the Ehime University. Eggs
were fixed with Bouinʼs fixative or Carlʼs fixative overnightand stored in 80% ethyl alcohol. Fixed eggs were stained withDAPI solution, and then observed with a fluorescencestereomicroscope under UV excitation. A part of eggs atearlier stages of embryonic development were processed intomethacrylate resin sections of 2 µm thickness. Sections werestained with Delafieldʼs hematoxylin, eosin G and fast green
FCF, and then observed with a biological microscope.
A sac-shaped embryo forms at the posteroventral side ofthe egg: its inner and outer layers are the embryo proper andamnion, respectively. The embryo elongates posteriorly
toward the anterior pole of the egg with its progressive
segmentation. When the caudal end of the embryo reaches
the anterior end of the egg, the abdomen bends and sinks intoyolk. After appendages formation, the embryo appears on to
the egg surface with its anteroposterior axis reversed. Afterthe embryo rotates 180 degrees around the egg longitudinalaxis, it acquires its definitive form to hatch out. In the present
study, we focused on the early embryonic development fromthe cleavage to formation of the embryo.
The cleavage of Reticulitermes speratus occurs
synchronously until at least 64-nucleus stage. Some cleavage
nuclei migrate to the egg surface at 32-nucleus stage andproliferate to form a single-cell layer. About 15 nuclei are left
in the yolk. At 200–240-cell stage, the inner cells proliferate,
and take their position between the center and posteroventral
side of the egg. Then, these inner cells concentrate to theposteroventral side of the egg, and the sac-shaped embryoforms, accompanied with the formation of amnioserosal fold.
We will further examine the embryonic development of R.
speratus covering the whole developmental stages, to discussand reconstruct the groundplan of Isoptera.

* Abstract of paper read at the 50th Annual Meeting of the Arthropodan Embryological Society of Japan, July 3–4, 2014 (Fuchu, Tokyo).