Occurrence of Antennal Glands in R. Renthal1, D. Velasquez1, D. Olmos1 and S. B. Vinson2 1The University of Texas at San Antonio, San Antonio, TX 78249; and 2Texas A&M University, College Station, TX 77843

INTRODUCTION: Secretory glands were discovered in the RESULTS: antenna of the red imported fire , Solenopsis invicta (Isidoro et al, 2000). The glands are located in the 9th of 10 antennal segments The species examined in this study are listed below. in workers and in the 9th and 10th of 11 segements in queens. The For species which displayed external pores in the outlets of the gland canals appear as a circumferential ring of pores antenna view by SEM, the name is printed in red. in the cuticle near the antennal segment joints (fig. 1 A & B). Male When both external pores and internal duct and gland fire ants lack antennal glands. Occasionally, secretions are structures were observed by TEM and/or SEM, the observed coming from the glands in queens (fig. 1 C). The function species name is printed in blue. Representative of these glands is unknown. There is some evidence for electron micrographs are shown in the figures. involvement of the gland secretion in queen recognition by workers (Kuriachan & Vinson, unpublished). Aside from S. invicta, there are Dolichoderinae no other reports of antennal glands in ants. We have now examined Dorymyrmex spp. a wide range of ant species to determine the distribution of antennal Forelius spp. glands. Linepithema humile

METHODS: Solenopsis and Ectatomma specimens were obtained Formicinae from the collection of the Smithsonian Institution National Museum Campanotus spp. of Natural History. Species assignments were made by the Oecophylla smaragdina Museum. All other specimens were from laboratory colonies Paratrechina spp. maintained at Texas A&M, with the exception of field-collected specimens of Pogonomyrmex sp., pharaonis, and Pseudomyrmecinae Oecophylla smaragdina. Antennae from dried museum specimens Pseudomyrmex ferruginea were transferred directly to SEM stubs. Live specimens were cold- anesthetized, fixed overnight in formalin, dehydrated through an Figure 3. Pores indicating antennal glands were found in all Solenopsis species examined. SEM images show the joint between segments 8 and 9 of worker antennae. All images are of museum ethanol series, and dried in a desiccator. Specimens for views of the Solenopsidini specimens ranging in age from 46-70 years after collection. inner surface of the antennal cuticle were treated with KOH by the Solenopsis aurea, S. clytemnestra, S. corticalis, S. method of Bin & Vinson (1986). SEM was done with a JEOL 840 desecheoensis, S. electra, S. fugax, S. gayi, S. microscope. geminata, S. globularia litoralis, S. interrupta, S. invicta, S. krockowi, S. latastei, S. macdonaghi, S. molesta, S. molesta validiuscula, S. pergandei, S. picea, S. picta, S. punctaticeps, S. quinquecuspis, S. richteri, S. tennesseensis, S. texana, S. wasmannii emery, S. xyloni, Monomorium minimum, M. pharaonis Figure 1. Antennal glands in A BC Solenopsis invicta Pores in Myrmicine tribe group cuticle near antennal segment Pogonomyrmex spp.,Tetramorium bicarinatum, A B joints from ducts leading to Pheidole spp. Figure 4. Antennal glands in Tetramorium bicarinatum. A. Cut-away view of segment 12 antennal glands. A. Workers Other (tip segment) of KOH-treated T. bicarinatum queen antenna. Cluster of spherical gland have glands in segment 9 of 10 Crematogaster spp. reservoirs visible at proximal end of segment. B. Higher magnification view of reservoirs, segments (scape = segment 1). showing gland ducts (arrows) leading to pores. Only ducts without reservoirs are observed in B. Queens have glands in worker antennae (not shown). C. External view of segment 12 of worker antenna showing segments 9 and 10 of 11 Ponerinae pores (arrows) which lead into ducts. segments. C. Occasionally Ectatomma ruidum, E. tuberlatum secretions are observed coming DISCUSSION: C from queen antennal glands. Cuticular pores were observed in antennal segment 9 near the joint with A B segment 8 in all 25 species of Solenopsis examined (fig. 3). This implies that antennal glands are a characteristic of all members of this . The presence of antennal glands does not extend to all members of the tribe Solenopsidini. Two species of Monomorium lack antennal glands. We also failed to find evidence for antennal glands in a wide variety of other ant species (fig. 2). However, we did observe antennal glands in Tetramorium bicarinatum, a Myrmicine ant in a different tribe from Solenopsis (fig. 4). The Figure 5. Inside surfaces of Solenopsis and Monomorium glands differ from those in Solenopsis as follows: i) they occur in all club antennae. A. Solenopsis invicta worker antennal segment segments; ii) in queens, they contain cuticular reservoirs; iii) the ducts 9. Gland ducts (arrows) penetrate the wall of the antenna penetrate the antennal wall through a flat surface, whereas Solenopsis ducts through an apodeme. B. Monomorium pharaonis worker antennal segment 12. No ducts are observed. exit through an apodeme (fig. 5).

REFERENCES:

Bin, F. and Vinson, S.B. (1986) Morphology of the antennal sex-gland in male Conclusions Trissolcus basalis (Woll.) an egg parasitoid of the green stink bug, Nezara viridula. Int. J. Morphol. and Embryol. 15, 129-138 1. Antennal glands are a characteristic trait of the genus Solenopsis. Isidoro, N., Romani, R., Velasquez, D., Renthal, R. and Vinson, S.B. (2000) Antennal glands in queen and worker of the , Solenopsis invicta Buren: first report in female social Aculeata (, Formicidae), Insectes Sociaux 47: 236-240 Figure 2. No evidence for antennal glands in workers from a wide range of representative ant 2. Morphologically different antennal glands occur in Tetramorium. species. A close examination was made of the segment joints in the club, if present, or the distal Acknowledgments: Supported by grants from the Texas Imported Fire 3 segments, in the absence of a club. No pores were seen along the segment joints. The figure Ant Research and Management Project and NIH G12 RR13646. We 3. The function and evolutionary origin of the glands is unknown. thank Ted Schultz and David Furth for their hospitality at the Smithsonian shows views of the joint between the third and second segment from the tip, analogous to the Institution National Museum of Natural History, and Marvin Edwards for location of the pores of the S. invicta antennal glands. Scale varies with specimen. contributing a specimen of M. pharaonis.

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