Recent Advances in Insect Embryology in Japan and Poland
Edited by H. Ando and Cz. Jura
Arthropod. EmbryoL. Soc. Jpn.
(lSEBU ·Co. Ltd., Tsukuba) 1987

195

Embryogenesis of the Leather Winged Beetle,
Athemus suturellus Motschulsky (Coleoptera, Cantharidae)*

Naoki FUJIWARA
and

Hisao KOBAY ASH I
Synopsis
External morphological events during embryogenesis in Athemus suturellus Motschulsky arestudied briefly. The embryo of A. suturellus develops on yolk surface without immersion into yolk,
and belongs to the superficial type of germ' band. The relationship between A. suturellus and fireflies is considered from the embryological standpoint.

Introduction
Although many studies on the embryogenesis of coleopteran insects have been
done, the embryonic development of the leather winged beetles, family Cantharidae ofCantharoidea, which contain.s Athemus suturellus has not been studied up to now. Other
families in the superfamily, Lampylidae and Drilidae (Omethidae) were studied
embryologically (William, 1916; Bugnion, 1922; Hess, 1922; Ando and Kobayashi,
1975; Kobayashi and Ando, 1985). Cantharoidea is supposed to be primitive group inpolyphagous coleopterans, but the systematic situation of this group in Coleoptera has
not yet been determined. In the present paper the authors described briefly theembryonic development of A. suturellus, by external observation and compared theobtained results with those of fireflies.

* Contributions from Sugadaira Montane Research Center, University of Tsukuba, No. 111.

N. Fujiwara and H. Kobayashi

196

Material and Methods
Adults of Athemus suturellus Motschulsky were collected at Sugadaira, Nagano Prefecture of Japan, from June to early August. The captured insects were reared by one
pair in each plastic case with plaster bottom. They were fed with aphids. Females deposited eggs on plaster of the case.
Eggs were fixed with alcoholic Bouin's fluid or F. A. A. at room temperature for
24 hr. Then they washed and preserved in 70 % alcohol. The chorion of eggs was removed with the aid of fine needles, and embryos were stained Mayer's haemalum forthe study of the external morphology. The eggs were stuck with needle, and they wereembedded in paraplast and were cut at 7 p. m-thick. The sections were stained with
Delafield's haematoxylin and eosin. First instar larvae were stained with eosin for twodays and were mounted on hollow slide glasses. The figures were drawn with theAbbe's apparatus.

Results
Total time duration from oviposition to hatching in Athemus suturellus is about 240
hours at room temperature, and the development process is divided into nine stages asshown in Table 1.
Table 1. Time table of embryonic development in Athemus suturellus.
Hours
after Oviposition

Stage of Development

o-

48 hr

Cleavage

48 -

68 hr

Formation and Completion of Blastoderm

68

80 hr

Formation of Germ Band-80 - 130 hr

Initiation and Completion of Segmentation130-

150 hrFormation of Appendages

150-

180 hrFormation of Mouthparts

180 - 200 hr
200- 230 hr

230 - 240 hr

Rotation of Embryo
Dorsal Closure of Embryo
Hatching

1. Newly laid egg

The eggs of A. suturellus are laid as a mass of 200 to 350 in number, cohered withsticky substance. The newly laid eggs are ellipsoidal and 600 X 450 P. m in size on anaverage, and they are soft, lustrous, smooth, and milky in color.

Embryogenesis of Athemus suturellus

197

1
100

50

30

y.L-______~~__~__________________~~~~~-----

100flmaFig. l.

Germ band of Athemus suturellus, about 80 hr after oviposition. a: lateral view, b:
ventral view. pI, protocephalon; po, protocorm.

2
pi
po

a

b

Fig. 2. Young embryo of Athemus suturellus, about 90 hr. a: lateral view, b: ventral view. pI,
protocephalon; po, protocorm.

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N. Fujiwara and H. Kobayashi

2. Cleavage

Although the process of maturation, fertilization and early cleavage could not be
observed in detail, it was noted that one nucleus with the cytoplasmic coat existed near
the anterior pole of the egg at a few hours after laying. The nucleus, which to be a
synkaryon, repeatedly divides mitotically during the subsequent two days.
3. Blastoderm formation

At about 48 hours after oviposition, energids begin to migrate gradually toward
the periplasm but some ones remain in the yolk as future primary vitellophages. Afterthe penetration of energids, about 25 p m in diameter, into the periplasm, the periplasm thickens and exhibits knobby protuberances inside. The nuclei (7-9 pm in diameter) in the periplasm continue to divide and distribute uniformly over there, to forma "syncytial blastoderm" . Then cell membranes appear between each nucleus, in result of this a "cellular blastoderm" completes, of which cells are spindle-shaped, 2 X 13
pm in size.

4. Formation of ventral plate and germ band

At about 72 hours after oviposition, an elliptic ventral plate is formed on the ventral region of the eggs, covering two thirds of egg length from the anterior pole, which
is about 200 p m in width and 300 p m in 'length.
At 80 hours after oviposition, the ventral plate begins to elongate and differentiates
into the protocephalon anteriorly and the protocorm posteriorly, which is 250 p m III
width and 350 p m in length (Fig. 1), and increases in thickness.
5. Segmentation of germ band

The protocephalon becomes concave at middle part, and the protocorm elongates
gradually and its segmentation begins (Fig. 2). At about 95 hours after oviposition, theprotocorm is composed of the mandibular, maxillary, and labial segments, and a
growth zone which is longer than other segments, and a primitive groove appears in
the protocorm. The germ band increases its length, along ventral side of egg, as thesegments are added one by one.
At about 5 hours later, in the germ band three gnathal, three thoracic and threeor four abdominal segments are visible, but the intercalary segment is not clear. At thesame time the labral rudiment appears as a pair of small lobes in the anterior region of
protocephalon (Fig. 3). At about 110 hours, the segmentation of the germ band continues further, and the caudal end of the germ band or embryo attains to the egg dorsal side over the posterior pole of the egg. The neural groove occurs along the midventralline of the embryo as a plain groove.
At about 120 hours, the segmentation of the embryo completes (Fig. 4), and thor-

Embryogenesis of Athemus suturellus

199

3
rtJ

c:

Cl

19nsl ths I abs

rtJ

-

..c:

rtJ
.0

ro

a

100 flmcbFig. 3. Segmentation of embryo of Athemus suturellus. a: about 100 hr, ventral view, b: about
110 hr, ventral view. c: about 110 hr, lateral view. abs, abdominal segment; gns,
gnathal segment; ths, thoracic segment.

4

ps

a
Fig. 4.

rtJ

ab10

..c:

100 flm

Completion of segmentation in embryo of Athemus suturellus, about 120 hr. a: lateralview, b: ventral view. abs, abdominal segment; abl, 10, first and tenth abdominal
segments; lis, labial segment; mds, mandibular segment; mxs, maxillary segment;
ps, pro thoracic segment; ths, thoracic segment.

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N. Fujiwara and H. Kobayashi

acic segments are broadest of all, and the fourth to tenth abdominal segments appear
being thinnest in the width. The stomodaeal invagination appears behind the paired
labral rudiments and the neural groove becomes clearer. At this stage the embryo consists of head lobes, intercalary, other three gnathal, three thoracic and ten abdominal
segments with the telson. At about 130 hours, the embryo attains to the longest stageand encircles the yolk mass.

6. Formation of appendages
With the beginning of appendage formation, the embryo becomes dwindled by degrees. At about 135 hours after oviposition, the rudiments of appendages are formed as
small protrusions on the gnathal and thoracic segments (Fig. 5 A), and the neuralridges become clear in the abdominal segments by development of the ganglia. Invagination of the stomodaeum deepens further behind the level of mandibular rudiments, and three pairs of swellings appear in the head lobes 'which may correspond to
the future protocerebrallobes.
The segmentaion of rudiments of the antennae, mandibles, maxillae, labium, andfore, mid and hind legs takes place at about 150 hours. The legs are directed medioposteriorly. The mandibular rudiments are prominent in the gnathal appendages, andthe maxillary ones are long and slender. Now the tips of antennal ones are over the intercalary segment (Fig. 5 B). In Luciola cruciata a pair of prominent pleuropodia isformed at the first abdominal segment (Ando and Kobayashi, 1975), but in A. suturellus
they are not found.

7. Formation of mouth parts
The remarkable morphogenesis in the embryo is the cephalization including transformation and translocation of the gnathal segments and appendages. At about 160
hours after oviposition, each segment of the thorax and abdomen becomes distinct, inconsequence of shrinkage of the embryonic length (Fig. 6 A) . The head lobes andgnathal segments begin to gather to form the future head at about 170 hours (Fig. 6
B). The labral rudiments unite to form a single developing labrum in front of the stomodaeum, and the antennal ones move latero-dorsally. The rudiments of mandible,
maxilla, and labium are assembled around the stomodaeum to form the future mouthparts together with the developing labrum. Figure 10 represents diagrammatically thisprocess in sequence. At this time the thoracic appendages are also segmented into thecoxa, trochanter, femur, tibia and pretarsus.

8. Revolution and dorsal closure of embryo
Until pre-cephalization stage the embryo has existed on the convex ventral surfaceof egg, but it begins to shorten again with the extension of both lateral extremities ofthe embryo. At about 180 hours the caudal end of the embryo reaches back near theEmbryogenesis of Athemus suturellus

201

SA
md

ab10

a

b

58

..... ::..:,.: .... .

a..... :.:"1.::.: .. .
......:.!.. :::.

b
1 00 ~m""",:".:: ...

.. ab 1 0

Fig. 5. Appendage formation of embryo of Athemus suturellus. A: about 135 hr, B: about 150
hr. A-a: lateral view, A-b: ventral view. B-a: lateral view, B-b: ventral view. abl,
10, first and tenth abdominal segments; at, antenna; li, labium; lr, labrum; md,
mandible; mx, maxilla; sd, stomodaeum; pt, prothorax.

N. Fujiwara and H. Kobayashi

202

6A

-ab1

b

a
6B

\ II

100 pmFig. 6.

Ir

md
at \ mxaty~.
limd-( .
mx

Iib

100 pmtion of mouth parts of Athemus suturellus. A: about 160 hr, B: about 170 hr. A-a:lateral view, A-b: ventarl view. B-a: lateral view, B-b: ventral view. abl, first abdominal segment; at, antenna; li, labium; lr, labrum; md, mandible; mx, maxilla.

Embryogenesis of Athemus suturellus

203

7

100 I'm

Fig. 7.

Pre-dorsal closure in embryo of Athemus suturellus, about 180 hr. a: lateral view, b:
head. at, antenna; md, mandible; mx, maxilla; li, labium.

8bFig. 8. Near completion of dorsal closure in embryo of Athemus suturellus, about 200 hr. a:lateral view, b: head. at, antenna; md, mandible; mx, maxilla; li, labium; sdo,
secondary dorsal organ.

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N. Fujiwara and H. Kobayashi

posterior pole of the egg, and the revolution of the embryo finished. Several hours after
the revolution the dorsal closure of embryo progresses (Fig. 7). During this time, aspindle-shaped secondary dorsal o~gan is formed in the dorsad of the embryo. The
coronal and frontal sutures appear, and the clypeus and gena are distinguished.
In about 190 to 195 hours, the embryo begins to lengthen again, and its caudal
end pushes forward along the ventral surface of the egg, and as a result of this growth,
the curvature of the embryo is reversed. The secondary dorsal organ becomes a discoidal form.

9. Embryo after dorsal closure
The coronal and frontal sutures become distinct, and the frons, clypeus and genaacquire their definitive forms. The tip of mandible becomes pointed, the maxilla turns
to the outside, the labrum retracts inside the mandibles, and the antennae move morelaterally. Consequently, the mouth parts of the first ins tar larva are completed (Fig. 8).
The labrum, clypeus and frons meet one another more compactly, and the labrum
becomes to be not visible from the outside.

10. Hatching
After the accomplishment of the dorsal closure, the young larva rends the chorion
in the site between the head and the abdominal end, and hatches out at about 10 days
after oviposition (Fig. 9). The first instar larva, which is milky in color, is about 1 mm
or more in length. I t has some microtrichiae on the thorax and the abdomen, except
the head, and a row of pili presents in the proximal part of each segment.

Discussion
The germ bands of insects are generally divided into three categories, that is, thesuperficial, invaginated and immersed. In Coleoptera the germ bands are generally
formed on the ventral surface of the egg, and there the further development also progresses. Therefore they belong to the superficial type, for instance, as in Hydrophilus piceus(Heider, 1889), Lytta viridana (Rempel and Church, 1969), Epilachna vigintioctomaculata(Miya and Abe, 1966) and so on.
The germ band of Athemus suturelius also belongs to this type, and the similar condition is found in other members of Cantharidae, Themus cyanipennis, T. midas andProthemus ciusianus (Fujiwara, unpublished).
In Lampyridae (Ando and Kobayashi, 1975; Kobayashi and Ando, 1985), however, one of the families of Cantharoidea, a ball-shaped germ rudiment is formed andthen sinks deeply into the yolk, and the following embryonic development proceeds
within the yolk. Consequently, it belongs to the so-called "immersed type" of germ
band which is the rare case in Coleoptera. As to the phylogeny of cantharoidean families, Crowson (1955) said that larvae of Lampyridae are the most primitive from theEmbryogenesis of Athemus suturellus

205

9100 flm

Fig. 9.

bFirst instar larva of Athemus suturellus. a: lateral view, b: head. at, antenna; md,
mandible; mx, maxilla; li, labium.

10-~-~Fig. 10. Diagrams of head formation of embryo of Athemus suturellus.
comparative morphology, on the contrary, Lycidae and Cantharidae are the most advanced. According to him, Lampyridae has the most primitive larvae in Cantharoidea,
but it has very specialized germ bands. In contrast, A. suturellus has the most specialized larvae in the same superfamily, but it has a general type of germ band, namely superficial one thought of more fundamental type in Coleoptera and other holometabolan
orders.

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N. Fujiwara and H. Kobayashi

Acknowledgments
The authors wish to express hearty thanks to Prof. Hiroshi Ando, SugadairaMontane Research Center, University of Tsukuba, for his cordial guidance, and invaluable suggestions as well as constant encouragement. Thanks also to Emeritus Prof.
Keiichiro Miya, Iwate University, for his valuable suggestions and kindness in looking
over the manuscript. We are indebted to Drs. Kazuo Haga, Ryuichiro Machida, Tohru
Kishimoto, and MSc. Hideyuki Uemiya, Institute of Biological Sciences, University ofTsukuba, for their helping in this study.

References
Ando, H. and H. Kobayashi, 1975. Description of early and middle developmental stages inembryos of the firefly, Luciola cruciata Motschulsky (Coleoptera, Lampyridae). Bull. Sugadaira
Bioi. Lab., Tokyo Kyoiku Univ. 7: 1-11.
Bugnion, E., 1922. Etudes relatives a l'anatomie et a l'embryologie des vers luisants ou Lampyrides. Bull. Bioi. France Be/g. 56: I-53.
Crowson, R. A., 1955. The Natural Classification of Col eo pt era. Nathaniel Lloyd, London.
Heider, K., 1889. Die Embryonalentwicklung von Hydrophilus piceus L. Gustav Fischer, Jena.
Hess, N. W., 1922. Origin and development of the light-organs of Photurus pennsylvanica De Geer.
J. Morphol. 36: 245-277.
Kobayashi, H. and H. Ando, 1985. Early embryogenesis of fireflies Luciola cruciata, L. lateralis andHotaria parvula. In H. Ando and K. Miya (eds. ), Recent Advances in Insect Embryology inJapan, 157-169. Arthropod. Embryo!. Soc. Jpn. (ISEBU Co. Ltd., Tsukuba).
Miya, K. and T. Abe, 1966. The early embryology of Epilachna vigintioctomaculata Motschulsky(Coleoptera, Coccinellidae), including some observation on the later development. J. Fac.
Agr., Iwate Univ. 7: 277-289.
Rempel, J. G. and N. S. Church, 1969. The embryology of Lytta viridana Le Conte (Coleoptera,
Meloidae). V. The blastoderm, germ layers, and body segments. Can. J. Zool. 47: 1157-1171.
Williams, F. X., 1916. Photogenic organs and embryology of Lampyrids. J. Morphol. 28: 145-207.

Authors' addresses: MAg. N. Fujiwara
Department of Oral Anatomy 11,
School of Dentisty, Iwate Medical
University, Morioka, Iwate 020,
Japan
Mr. H. Kobayashi
Shiojiri Municipal Junior HighSchool, Shiojiri, Nagano 399-64,
Japan