Journal of Chemical Ecology, Vol. 10, No. 10, 1984 IDENTIFICATION OF TRAIL PHEROMONE OF THE ANT Tetramorium caespitum L. (HYMENOPTERA: MYRMICINAE) ATHULA B. ATTYGALLE and E. DAVID MORGAN Department of Chemistry, University of Keele Staffordshire, ST5 5BG, U.K. (Received December 1, 1983; revised February 16, 1984) Abstract--The trail pheromone of the ant Tetramorium caespitum L. is a 70:30 mixture of 2,5-dimethylpyrazine and 3-ethyl-2, 5-dimethylpyrazine. The average total amount of the two pyrazines present in the poison vesicle was found to be 3.9 ng per ant, of which 2.7 _+ 0.4 ng is 2,5-dimethylpyrazine and 1.15 + 0.25 ng is 3-ethyl-2,5-dimethylpyrazine. The pyrazines con- stitute only 0.03% of the volume of the poison vesicle but account for the whole of the trail-following activity. A 70:30 mixture of the respective pyrazines evoked the highest activity in artificial trail-following tests. Key Words--Ant, Tetramorium caespitum, trail pheromone, 2,5-dimeth- ylpyrazine, poison gland, venom, Hymenoptera, Myrmicinae, synergism. INTRODUCTION A large number of ant species are known to employ trail pheromones as a means of communication, but only in a very few cases has the pheromone been chemically identified. The first trail substance to be identified was methyl 4-methylpyrrole-2-carboxylate from Atta texana Buckley (Tumlinson et al., 1972). The same compound was subsequently demonstrated to be active in evoking trail following in A. cephalotes L. (Riley et al., 1974) and Aero- myrmex octospinosus Reich (Robinson et al., 1974). 3-Ethyl-2,5-dimethylpyrazine has been shown to be the major com- ponent of the trail pheromone ofAtta sexdens rubropilosa Forel (Cross et al., 1979), and the same compound has since been identified as the single com- ponent of the trail pheromone of eight species of Myrmiea (Evershed et al., 1981, 1982). In the beginning of the present study, only the aforementioned 1453 0098-0331/84/1000-1453503.50/0 9 1984 Plenum Publishing Corporation