600 J. Entomol. Sci. Vol. 25, No. 4 (1990) Robinson, W. S., J. C. Moser, M. S. Blum and E. Amante. 1974. Laboratory investigations of the trail following responses of four species of leap cutting ants with notes on the specificity of a trail pheromone of Atta tewna (Buckley). Insectes Sociaux 21: 87-94. Schneider, D. 1957. Electrophysiologische Untersuchungen von Chemo- und Mechanore- zeptoren der Antenne des Seidenspinners Bornbyx mori L. 2. vergl. Physiol. 40: 8-41. Sonnet, P. E. and J. C. Moser. 1973. Trail pheromones: Responses of the Texas leafcutting ant, Attu texana to selected halo- and cyanopyrrole-2-aldehydes, ketones, and esters. Environ. Entomol. 2: 851-854. Stliedler, E. and F. E. Hanson. 1975. Olfactory capabilities of the "gustatory" chemo- receptors of the tobacco hornworm larvae. J. comp. Physiol. 104: 97-102. Ilumlinson, J. H., J. C. Moser, R. M. Silverstein, R. G. Brownlee and J. M. Ruth. 1971. Identification of the trail pheromone of a leaf cutting ant, Atta texana. Nature 234: 348-349, Weber, N. A. 1972. Gardening ants - The attines. Mem. Am. Phil. Soc. 92: 1-146. Antenna1 Olfactory Responsiveness of the Texas Leaf C rM. Ant (Hymenoptera: Formicidae) to Trail and its Tvvo Alarm Substmcesl N. A. Andryszak, T. L. Payne2, J. C. Dickens3, J. C. Moser.L, and R. W. Fisher Department of Entomology, Texas Agricultural Experiment Station, Texas A & M University, College Station, TX 77843z J. Entomol. Sci. 25(4): 593-600 (October 1990) ABSTRACT Electsoantennograms (EAGs) were recorded from major workers, queens, and males of the Texas leaf cutting, Attu texana (BucMey) wpenoptera: Forrnicidae) in response to serial dilutions of two alarm subsbnces, 2-hephone and 4-methyl-3-heptanone, and its trail pheromone, 4-methylpynole-2-carboxylate. The lower EAG threshold for major workers relative to queens and males for both alarm substances correlated well with previously reported behavioral bioassays which showed workers to be most responsive to these odorants. Although Iaboratory behavioral bioassays showed minor workers, queens, and males to have a similar behavioral threshold for the trail pheromone, minor workers were more responsive to higher concentrations of the trail pheromone. However, EAGs revealed queens si~iflicantly more sensitive and responsive to the trail pheromone than the other castes. These seedngly eniwatic results are discussed with regard to A. texana biology and receptor physiology. KEY WORDS Leaf cutting ant, Atta texana, olfaction, trail pheromone, electro- antennogram, EAG, trail pheromone, behavior. The Texas leaf cutting ant or town ant, Atta texana (Buckley), Is the northern- most species of the genus and the largest of the fungus growing ants (Weber 1972). These ants are found in Louisiana and Texas (Cameron and Riggs- 1985). Studies on the chemical communication systems of A. texana (Moser 1983), and other ants (Bradshaw and Howse 1984) have primarily concerned the identification of various pheromones, and determination of the b e b ~ o r a 1 effects of the pheromones in laboratory bioassays and field tests. In this regard, the trail foHodng pheromone of A. texana was identified as 4-methylpyrrole-2-carboxylate (Tumlinson et al. 1971), and 2-heptanone and 4-methyl-Bheptanone were shown to function as alarm substances (Moser et el. 1968). Until the study reported here, no investigations have been conducted to determine the antennal olfactory response of Atta texana to its trail and alarm pheromones. In fact, in only a few instances have electro- physiological studies been conducted to determine receptor responses to pheromones in any ant species (Dumpert 1972; Masson and Friggi 1971, 1974; Payne et al. 1975; Glancey and Dickens 1987). The purpose of the study presented here was to determine the antennal olfactory response sensitivity -- of castes of A. texuna to the trail pheromone, 4- I Accepted for publication 26 August 1990. Department of Entomology, VPI & SU, Blacksburg, VA 24061-0319; reprint requests. USDA-ARS, Boll Weevil Research Unit, Mississippi State, MS 39762. USDA-FS, Southern Forest Expeiiment Station, 2500 Shreveport Hq, PinevilIe, LA 71360. 593