International
Journal of
Insect Morphology
isf
PERGAMON
Embryology
International Journal of Insect Morphology and Embryology 28 (1999) 331-335
www.elsevier.com/locate/ijinsectme
Exocrine glands in the antennae of the carabid beetle, Platynus
assimilis (Paykull) 1790 (Coleoptera, Carabidae, Pterostichinae)
Alexander Weisa, Klaus Schonitzerb, Roland R. Melzera'*
^Zoologisches Institut der Universitdt, Luisenstr. 14, D-80333, Miinchen, Germany
b
Zoologische Staatssammlung, Munchhausenstr. 21, D-81247, Miinchen, Germany
Received 6 August 1999; accepted 18 October 1999
Abstract
The antennae of males and females of the carabid beetle, Platynus, contain numerous type-Ill gland acini composed of two
different gland cells and a canal cell. The findings show that antennal glands are not only found in highly specialized groups, but
also in beetles thought to represent ancestral character states. However, in most cases the function of these glands is not well
understood. © 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Gland acini; Antennomere; Fine structure; Insecta
1. Introduction
Insect antennae are well known as bearers of longrange sense organs. Contrary to this, our knowledge of
the distribution and function of antennal exocrine
glands throughout the Insecta is fragmentary. In some
insects well developed glands are present within the
antennae, e.g. in some parasitic Hymenoptera (Bin et
al., 1989) and in some Coleoptera as well, mainly myrmeco- and termitophilous genera (Cammaerts, 1974).
To help understand whether these glands are found
only in some highly specialized forms or if they are
among the more general (and commonly distributed)
antennal features we have investigated the antennae of
an adephagous beetle generally thought to represent
somewhat ancestral coleopteran character' states, the
carabid Platynus. We show that both males and
females of this genus possess numerous gland units
within their antennae. This supports the idea that at
• Corresponding author. Tel: +49-89-5902-262; fax: + 49-89-5902450.
E-mail address: [email protected] (R.R. Melzer).
least among Coleoptera exocrine antennal glands are
widely distributed.
2. Materials and methods
Platynus males and females were collected at locations around Munich and determined according to
the key of Freude (1976). The specimens used in this
study were prepared according to SEM and TEM
standard techniques.
Fixation was done with 4% glutardialdehyde in
0.1 M cacodylate buffer (pH 7.1) and postosmication
(1% osmium tetroxide in buffer). After dehydration in
a graded acetone series, TEM specimens were
embedded in the Epon equivalent, Glycidether 100,
sectioned with glass knives on a LKB Ultrotome II,
double stained with uranyl acetate and lead citrate on
a LKB 2186 stainer, and inspected with a Philips CM
10 at 80 kV.
The semithin sections (1-1.5 μm) used for Fig. 3C
were stained with Richardson's agens. The SEM specimens were critical-point dried in a Polaron E 3000 CP
dryer from CO2, sputtered with gold (Bio Rad SEM
0020-7322/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S 0 0 2 0 - 7 3 2 2 ( 9 9 ) 0 0 0 3 4 - 3
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i. Weis et al. / International Journal of Insect Morphology and Embryology 28 (1999) 331-335
coating system) and studied with a Philips XL20 at
between 4 and 25 kV.
3. Results
roundish cuticular cupola that are present from the
fourth antennomere to the antennal tip. While the
smaller pores are gland pores, the larger ones might
belong to Sensilla coeloconica or ampullacea due to
their cupola.
3.1. External morphology
3.2. Distribution of gland units within the antennal
cross-section
By external inspection with the scanning EM, one
finds numerous pores randomly distributed on the eleven articles of the antennae of Platynus males and
females (Fig. 1A and B). These pores are interspersed
among the regular pattern of epidermal cells and have
a diameter of 0.6-1.65 μm. They differ from larger
pores (1.5-2.2 μm) each sitting in the centre of a
Using the light microscope and the transmission
EM, it becomes obvious that the smaller pores are
connected with gland units that are densely arranged
at the base of the antennal epidermis and fill a considerable portion of the antennal mixocoele cavity
(Fig. 1C). In the proximal regions of the antennal
Fig. 1. (A) Antennomeres nos. 3-5 of a female Platynus, viewed with the SEM; bar 200 \an. (B) SEM-view of antennal article no. 9 of a male
Platynus. Between the sensory hairs, gland pores can be seen (white arrowheads). Note larger pores (white arrows) sitting in the centre of a small
cupola probably representing Sensilla coeloconica; bar 20 nm. (C) Survey of gland acini situated close to the antennal cuticle within article no. 5
of a female Platynus, TEM, cross-section. A axon bundles, Cu cuticle, gll gland cell, N gland cell nucleus, arrowheads cuticular canals of various
gland units; bar 2 μm.
A. Weis et al. / International Journal of Insect Morphology and Embryology 28 (1999) 331-335
333
Fig. 2. (A), (B) and (C) Transversal sections of antennal article no. 5 of a female Platynus, TEM. Two gland units each can be distinguished, gll
and gl2 gland cells, cc canal cell, arrowheads microvillous borders of secretory cells adjacent to the cuticular canal; bars 2 μ^i. (D) and (E) Details
showing the cuticular canal and its microvillous borders in longitudinal (D) and cross-section (E). Note pore tubules between microvilli and
canal lumen (white arrows); bars 0.5 μm (D), 1 μm (E).
334
A. Weis et al. j International Journal of Insect Morphology and Embryology 28 (1999) 331-335
articles, close to the joints, antennal cross-sections
reveal two portions of antennal haemolymph sinus, a
dorsal and a ventral one, separated by a cuticular
ridge (Fig. 3C). Within the dorsal haemolymph sinus
one finds two antennal nerves, tracheas and a blood
sinus running distally from the antennal joint. Close to
the cuticle, numerous gland acini and canals can be
seen. Especially in the ventral part of the antennal
cross-section, they fill the lumen almost completely.
3.3. Fine structure of the gland acini
Each gland acinus is composed of three cells aligned
one after another, two gland cells and one canal cell
(Figs. 1C, 2 and 3B). The most proximal gland cell
contains a central extracellular space densely filled
with microvilli from which a canal extends distally to
the pores (Fig. 2). The second gland cell, situated more
distally, is also equipped with microvilli adjacent to
the canal. Here a thin cuticle can be seen that contains
numerous pores and pore tubules that apparently let
the secretion pass (Fig. 2D and E). The cytoplasm of
the gland cells contains numerous vesicles filled with
homogenous material surrounding the microvillous
borders. Neighbouring the nucleus, both rough and
smooth ER cisternae are abundant. The third cell or
canal cell is deprived of microvilli, and forms the distal
part of the cuticular canal extending distally to the
pore (Fig. 3B).
4. Discussion
The cellular architecture of these gland units corre-
Cu
Fig. 3. (A) Survey of antennomeres nos. 3-5 giving the position of the antennal cross-section depicted in C. (B) Schematic reconstruction of a
gland acinus with adjacent epidermis and cuticle. (C) Cross-section of an antennal article close to the joint with the two main portions of gland
tissue. The upper lumen has a relatively large haemolymph sinus containing two antennal nerves (An), tracheae (Tr) and a blood vessel (V),
while the lower lumen is almost completely filled by gland cells. Arrowheads and P gland pores, BL basal lamina, C canal, Cu cuticle, E epidermis cell, gll, gl2 gland cells, N nucleus.
A. Weis et al. / International Journal of Insect Morphology and Embryology 28 (1999) 331-335
sponds well with type-III exocrine glands as defined by
Noirot and Quennedey (1974, 1991). These glands are
ubiquitous among insects, and are found on almost
every region of the body in various taxa. Regarding
the antennae, they have been reported for parasitic
hymenopterans like the scelionid Trissolcus (Bin et al.,
1989) and the eulophid Melittobia (Dahms, 1984). In
addition they have been described for coleopterans, especially myrmeco- and termitophilous groups, e.g. Pselaphidae (Cammaerts, 1974) and Paussidae (Mou,
1938), but they are also found in the staphylinid Aleochara (Skilbeck and Anderson, 1994), in some chrysomelids (Bartlet et al., 1994), catopids (Martin, 1975)
and meloids (Matthes, 1970). Depending on their distribution among females and males, and the general
life habits of the studied insects, they have been suspected to represent either appeasement glands, pheromone glands, kaironome glands or a kind of lubricant
for the antennae and their sensilla (surveys in Bin et
al. (1989), Skilbeck and Anderson (1994) and Dahms
(1984)). The presence of antennal glands in various
coleopterans, both Adephaga with antennae of a more
ancestral type (this study) and Polyphaga with highly
specialized antenna indicates that they might be common among this group of insects and represent one of
their basic antennal features.
Acknowledgements
We thank Hedwig Gebhard (Munich) for expert
technical assistance and Helga Posch (Munich) for
improving the English.
335
References
Bartlet, E., Isidoro, N., Williams, I.H., 1994. Antennal glands in
Psylliodes chrysocephala, and their possible role in reproductive
behaviour. Physiological Entomology 19, 241-250.
Bin, F., Colazza, S., Isidoro, N., Solinas, M., Vinson, S.B., 1989.
Antennal chemosensilla and glands, and their possible meaning in
the reproductive behaviour of Trissolcus basalis (Woll.) (Hym:
Scelionidae). Entomologica 24, 33—97.
Cammaerts, R., 1974. Le systeme glandulaire tegumentaire du
coleoptere myrmecophile Claviger testaceus Preyssler, 1790
(Pselaphidae). Zeitschrift fur Morphologie der Tiere 77, 187-219.
Dahms, E.C., 1984. An interpretation of the structure and function
of the antennal sense organs of Melittobia australica
(Hymenoptera: Eulophidae) with the discovery of a large dermal
gland in the male scape. Memoires of the Queensland Museum
21, 361-385.
Freude, H., 1976. Adephaga, 1. Carabidae. In: Freude, H., Harde,
K.W., Lohse, G.A. (Eds.), Die Kafer Mitteleuropas, Bd. 2.
Goecke und Evers, Krefeld, pp. 1-302.
Martin, N., 1975. Ultrastructure des glands dermiques de l'antenne
d'un
Coleoptere cavernicole troglophile,
Choleva spec.
(Coleoptera, Silphidae). Zeitschrift fur Morphologie der Tiere 80,
261-275.
Matthes, D., 1970. Die Fachelbalz von Cercoma schdfferi (L.)
(Coleoptera,
Meloidae).
Verhandlungen
der
deutschen
Zoologischen Gesellschaft 63, 316-322.
Mou, Y.C., 1938. Morphologische und histologische Studien iiber
Paussidendriisen.
Zoologisches Jahrbuch (Anatomie und
Ontogenie der Tiere) 64, 287-346.
Noirot, C.H., Quennedey, A., 1974. Fine structure of insect epidermal glands. Annual Review Entomology 19, 61-80.
Noirot, C.H., Quennedey, A., 1991. Glands, gland cells, glandular
units: some comments on terminilogy and classification. Annales
de la Societe Entomologique de la France (NS) 27, 123-128.
Skilbeck, C.A., Anderson, M., 1994. The fine structure of glandular
units on the antennae of two species of the parasitoid, Aleochara
(Coleoptera: Staphylinidae). International Journal of Insect
Morphology and Embryology 23, 319-328.