Structure and distribution of antennal sensilla of the red imported fire ant
Introduction
The social behavior of ants depends on communication between individuals (Hölldobler and Wilson, 1990). The antenna is a major channel of sensory input, including receptors for volatile odors and pheromones, contact chemoreception, water vapor, carbon dioxide, sound, proprioception, and touch (Jaisson, 1969, Masson and Gabouriaut, 1973, Fresneau, 1979, Hashimoto, 1990, Ehmer and Gronenberg, 1997, Kleineidam et al., 2000). Several models for ant colony organization emphasize the importance of interactions between individual colony members (Detrain and Deneubourg, 1997, Franks and Deneubourg, 1997, Cassill and Tschinkel, 1999, Gordon and Mehdiabadi, 1999, Backen et al., 2000). These interactions undoubtedly have both genetic and experiential determinants. The extent to which individual workers either have or do not have certain types or configurations of sensory receptors or sensory processing pathways could influence their behavior. A detailed scanning electron microscopy (SEM) survey of the sensilla on the antennae of many ant species was previously reported by Hashimoto (1990). The studies presented in this paper focus on the red imported fire ant, Solenopsis invicta, an agricultural and urban pest species in the southern United States (Vinson and Greenberg, 1986, Ross and Keller, 1995). The genus Solenopsis was not included in Hashimoto's (1990) survey. We present studies of S. invicta olfactory sensilla, which are the first detailed analyses of these structures in ants.
Section snippets
Ants
Polygyne colonies of S. invicta were collected in Bexar County, TX from mounds and about 15 cm of underlying soil, using the floatation method (Jouvenaz et al., 1977). The resulting lab colonies were only a portion of the original colony, but most contained thousands of workers along with brood and several queens. Lab colonies were maintained in plastic trays, essentially by the method described by Vargo and Hulsey (2000), except each colony had only a single plaster nest, and lighting was an
Sensilla on the worker's antenna
The antenna contains 10 antennomers. The numbers of sensilla on each antennomer are listed in Table 1. The long scape (A1) and conical pedicel (A2) are typical of female ant antennae (see Isidoro et al., 2000, Renthal et al., 2002 for a more complete description of the segment nomenclature). The pedicel of S. invicta is similar to Campanotus, described by Masson and Gabouriaut (1973), containing the scolopidia of Johnston's organ, which are visible at the junction with the funiculus, and also
Discussion
Several caste differences occur in antennal morphology of S. invicta. The most prominent is the sexual dimorphism between males and females. Male S. invicta antennae have a short scape compared to the female, a common sexual dimorphism in ants (Hölldobler and Wilson, 1990). In addition, striking differences are found between sensilla types on male and female antennae. The males completely lack s. basiconica. Most of the male sensilla are s. tricodea curvata, and most are approximately the same
Acknowledgements
This work was supported by a grant from the Texas Imported Fire Ant Research and Management Program, and was also supported in part by the Cajal Neuroscience Research Center at the University of Texas at San Antonio, funded by NIH RCMI grant RR13646. We thank Brad Vinson for helpful discussions and advice, Deby Cassill for reviewing the manuscript, Paul Farnsworth and Peggy Miller for assistance with TEM, and Kalpana Penumanu, Kalyani Guntur and Peter Hemond for technical assistance. This paper
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