PERGAMON International Journal of Insect Morphology and Embryology 28 (1999) 331-335

InternationalJournal of

Insect Morphologyisf

Embryology

www.elsevier.com/locate/ijinsectme

Exocrine glands in the antennae of the carabid beetle, Platynusassimilis (Paykull) 1790 (Coleoptera, Carabidae, Pterostichinae)

Alexander Weisa, Klaus Schonitzerb, Roland R. Melzera'*

^Zoologisches Institut der Universitdt, Luisenstr. 14, D-80333, Miinchen, GermanybZoologische 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 twodifferent gland cells and a canal cell. The findings show that antennal glands are not only found in highly specialized groups, butalso in beetles thought to represent ancestral character states. However, in most cases the function of these glands is not wellunderstood. © 2000 Elsevier Science Ltd. All rights reserved.

Keywords: Gland acini; Antennomere; Fine structure; Insecta

1. Introduction

Insect antennae are well known as bearers of long-range sense organs. Contrary to this, our knowledge ofthe distribution and function of antennal exocrineglands throughout the Insecta is fragmentary. In someinsects well developed glands are present within theantennae, e.g. in some parasitic Hymenoptera (Bin etal., 1989) and in some Coleoptera as well, mainly myr-meco- and termitophilous genera (Cammaerts, 1974).To help understand whether these glands are foundonly in some highly specialized forms or if they areamong the more general (and commonly distributed)antennal features we have investigated the antennae ofan adephagous beetle generally thought to representsomewhat ancestral coleopteran character' states, thecarabid Platynus. We show that both males andfemales of this genus possess numerous gland unitswithin their antennae. This supports the idea that at

• Corresponding author. Tel: +49-89-5902-262; fax: + 49-89-5902-

450.E-mail address: melzer@zi.biologie.uni-muenchen.de (R.R. Mel-

zer).

least among Coleoptera exocrine antennal glands arewidely distributed.

2. Materials and methods

Platynus males and females were collected at lo-cations around Munich and determined according tothe key of Freude (1976). The specimens used in thisstudy were prepared according to SEM and TEMstandard techniques.

Fixation was done with 4% glutardialdehyde in0.1 M cacodylate buffer (pH 7.1) and postosmication(1% osmium tetroxide in buffer). After dehydration ina graded acetone series, TEM specimens wereembedded in the Epon equivalent, Glycidether 100,sectioned with glass knives on a LKB Ultrotome II,double stained with uranyl acetate and lead citrate ona LKB 2186 stainer, and inspected with a Philips CM10 at 80 kV.

The semithin sections (1-1.5 μm) used for Fig. 3Cwere stained with Richardson's agens. The SEM speci-mens were critical-point dried in a Polaron E 3000 CPdryer from CO2, sputtered with gold (Bio Rad SEM

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PII: S0020-7322(99)00034-3

332 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

3.1. External morphology

By external inspection with the scanning EM, onefinds numerous pores randomly distributed on the ele-ven articles of the antennae of Platynus males andfemales (Fig. 1A and B). These pores are interspersedamong the regular pattern of epidermal cells and havea diameter of 0.6-1.65 μm. They differ from largerpores (1.5-2.2 μm) each sitting in the centre of a

roundish cuticular cupola that are present from thefourth antennomere to the antennal tip. While thesmaller pores are gland pores, the larger ones mightbelong to Sensilla coeloconica or ampullacea due totheir cupola.

3.2. Distribution of gland units within the antennal

cross-section

Using the light microscope and the transmissionEM, it becomes obvious that the smaller pores areconnected with gland units that are densely arrangedat the base of the antennal epidermis and fill a con-siderable 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-sectionsreveal two portions of antennal haemolymph sinus, adorsal and a ventral one, separated by a cuticularridge (Fig. 3C). Within the dorsal haemolymph sinusone finds two antennal nerves, tracheas and a bloodsinus running distally from the antennal joint. Close tothe cuticle, numerous gland acini and canals can beseen. Especially in the ventral part of the antennalcross-section, they fill the lumen almost completely.

3.3. Fine structure of the gland acini

Each gland acinus is composed of three cells alignedone after another, two gland cells and one canal cell(Figs. 1C, 2 and 3B). The most proximal gland cellcontains a central extracellular space densely filledwith microvilli from which a canal extends distally to

the pores (Fig. 2). The second gland cell, situated moredistally, is also equipped with microvilli adjacent tothe canal. Here a thin cuticle can be seen that containsnumerous pores and pore tubules that apparently letthe secretion pass (Fig. 2D and E). The cytoplasm ofthe gland cells contains numerous vesicles filled withhomogenous material surrounding the microvillousborders. Neighbouring the nucleus, both rough andsmooth ER cisternae are abundant. The third cell orcanal cell is deprived of microvilli, and forms the distalpart of the cuticular canal extending distally to thepore (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 agland acinus with adjacent epidermis and cuticle. (C) Cross-section of an antennal article close to the joint with the two main portions of glandtissue. 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 epider-mis cell, gll, gl2 gland cells, N nucleus.

A. Weis et al. / International Journal of Insect Morphology and Embryology 28 (1999) 331-335 335

sponds well with type-III exocrine glands as defined byNoirot and Quennedey (1974, 1991). These glands areubiquitous among insects, and are found on almostevery region of the body in various taxa. Regardingthe antennae, they have been reported for parasitichymenopterans like the scelionid Trissolcus (Bin et al.,1989) and the eulophid Melittobia (Dahms, 1984). Inaddition they have been described for coleopterans, es-pecially myrmeco- and termitophilous groups, e.g. Pse-laphidae (Cammaerts, 1974) and Paussidae (Mou,1938), but they are also found in the staphylinid Aleo-chara (Skilbeck and Anderson, 1994), in some chry-somelids (Bartlet et al., 1994), catopids (Martin, 1975)and meloids (Matthes, 1970). Depending on their dis-tribution among females and males, and the generallife habits of the studied insects, they have been sus-pected to represent either appeasement glands, phero-mone glands, kaironome glands or a kind of lubricantfor the antennae and their sensilla (surveys in Bin etal. (1989), Skilbeck and Anderson (1994) and Dahms(1984)). The presence of antennal glands in variouscoleopterans, both Adephaga with antennae of a moreancestral type (this study) and Polyphaga with highlyspecialized antenna indicates that they might be com-mon among this group of insects and represent one oftheir basic antennal features.

Acknowledgements

We thank Hedwig Gebhard (Munich) for experttechnical assistance and Helga Posch (Munich) forimproving the English.

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