Antennal glands in queen and worker of the fire ant, Solenopsis invicta Buren: first report in female social Aculeata (Hymenoptera, Formicidae)

Abstract

The antennae of the higher Hymenoptera (ants, bees and wasps) have been presumed to be exclusively sensory appendages, although the antennae of a number of the Parasitica also support a variety of glands. Using both SEM and TEM we show the presence of ectodermal glands in the antennae of workers and queens, but not in the males, of the Imported Fire Ant, Solenopsis invicta Buren. These glands and their associated pores are present on a glabrous proximal region of A9 of the antennae of workers and both A9 and A10 of queens. The pores leading to the bicellular secretory units in the antennae are more numerous on A10 of the queen followed by A9 of workers and in both cases they form a uniform ring around the segment. However, the pores on A9 of the queen are more numerous on the dorsal surface. While a paste-like secretion can sometimes be seen emerging from the pores of workers, this material is commonly seen from the pores of queen antennae. In social Aculeata, antennal glands have previously been found only in males of some vespids. This report, the first for ants and the first for females of social Aculeata, gives evidence for antennal glands in S. invicta.

Occurrence of antennal glands in ants

“…Pores on the external surface are visible where canals from the antennal glands pass through the cuticle, as previously shown (Isidoro et al, 2000). Figures 1A and 1B show pores in workers and queens, respectively, near antennal segment joints.…”

“…In addition to the glands of the distal funiculus described here and previously (Isidoro et al, 2000), glands have been observed in the scape of three ant species: Eciton burchelli (Billen, 2000), and Polyergus rufescens and Formica cunicularia (Romani et al, 2006). Also, both type 1 and type 3 glands were observed in all antennomers except the scape of the primitive ant Dinoponera lucida (Marques-Silva et al, 2006).…”

“…There is some evidence for involvement of the gland secretion in queen recognition by workers (Kuriachan and Vinson, unpublished). Aside from the observations of Isidoro et al (2000), there are no other published reports of similar antennal glands in ants, although a thorough survey of antenna morphology from about 50 ant species (not including Solenopsis ) was presented by Hashimoto (1990). We have now examined a wide range of ant species to determine the distribution of type 3 antennal glands in the distal funiculus.…”

“…Since then antennal glands have been reported in a number of Hymenoptera (Isidoro et al, 1996; Goettler et al, 2006) and beetles (Giglio et al, 2005; Weis et al, 1999). Although glands were reported from the antennal club of female red imported fire ants, Solenopsis invicta Buren, 1972 (Isidoro et al 2000) and the scape of an army ant, Eciton burchelli (Billen 2000), the flagellum of a primitive Ponerinae, Dinoponera lucida (Marques-Silva et al, 2006) and the antennae of a slave-making formicine ant (Romani et al, 2006) little is known about other genera. The glands of S. invicta are located in the 9th of 10 antennal segments in workers and in the 9th and 10th of 11 segments in queens.…”

“…Occasionally, secretions are observed coming from the glands in queens. The gland cells are penetrated by cuticular canals which terminate in external pores (Isidoro et al, 2000 and are thus classified as class 3 cells, in contrast to classes 1 and 2, in which the gland cell lacks a cuticular canal (Noirot and Quennedy, 1974). The function of these glands is unknown.…”