Physiological Entomology zyxwvutsr (1988) zyxwvu 13, 251-265 Identification of a component of the trail pheromone of the ant zyxwvu Pheidole pullidulu (Hymenoptera: Formicidae) MAHMOUD FADL ALI, E. DAVID MORGAN, CLAIRE DETRAIN* and ATHULA B. ATTYGALLEt Department of Chemistry, University of Keele, U.K., *Labmatoire de Biologie Animale, University of Brussels, Belgium, and $Institute for Organic Chemistry 11, University of Erlangen-Nuremburg, Erlangen, F.R.G. ABSTRACT. The poison gland of minor workers of P.pallidu1a Nyl. contains 3-ethyl-2,5-dimethylpyrazine which induces trail-following in other workers, but does not account for the full trail-following effect of one worker’s poison gland. No pyrazines were detected in major workers and their glands do not contain the pheromone. Key words. Ant, trail pheromone, Pheidole, poison gland, minor workers, 3-ethyl-2,s-dimethylpyrazine. zyxw Introduction Among zyxwvutsr 400 species of Pheidole found throughout the world, only three are found in Europe, and of these, only Pheidole pallidula Nyl. is indigenous there. P.pallidula and Plagiolepis pygmaea are the two most abundant species of ant in the Mediterranean area. The principle characteristic of P .pallidula is the possession of two subcastes of workers, distinct in their morphology (Bernard, 1968). The minor workers are very small (c. 2-2.5 mm long), the major workers are larger (3 mm) with very large heads and powerful mandibles. There is high diversity of polyethism during food recruitment between majors and minors in different Pheidole species. For example, majors of several New World Pheidole species are never involved in food retrieval and do not lay chemical trails, but both castes in P.rugulosa and P.sciophila partici- pate in foraging and trail-laying (Holldobler & Moglich, 1980). The minors of P.pallidula are responsible for food-discovery and recruitment Correspondence: Dr E. D. Morgan, Department of Chemistry, University of Keele, Staffordshire ST5 5BG. of nestmates. Only a few majors follow the chemical trail, sometimes carrying food (Detrain, 1984). Morphological and chemical differences between the two sub-castes also exist in the abdominal glands (Poison, Dufour and pygidial glands) (Detrain et nl., 1987). To learn something of the behaviour of the workers, we have studied the trail pheromone of the species, and attempted to quantify it in the two subcastes. We show here that the trail pheromone is found only in the minor workers, although both subcastes follow trails. We have identified one substance in the gland which evokes trail-following, but it alone does not account for the full trail-following effect of a minor worker gland. Materials and Methods Maintenance of the colonies The ants (P.pallidula, also Myrmica and Teframorium species) were reared in artificial nests made from zyx glass flasks (250 ml), the bot- toms of which were covered with moistened plaster of Paris. Each flask was placed in a plastic 257