1LEPCO,Université François Rabelais, Parc de Grandmont, 37200 Tours, France.
2Institut Für Organishe chemie, Universität Hamburg, Martin Luter King Platz D-20146 Hamburg, Germany.
3George S. Wise faculty of Life Sciences, Tel-Aviv University, Ramat Aviv 69978, Israel.
The dulotic ant Polyergus rufescens is unable to found a new colony independently. Newly-mated females find and penetrate a colony of the host species, kill the resident queen and get adoption by the host workers. Successful usurpation by newly-mated females seems to depend on a dual strategy: being chemically insignificant with respect to cuticular hydrocarbons (D'Ettorre et al., 1999), and repelling prospective host nest attackers. We identified the Dufour's gland compounds of P. rufescens gynes and workers by GS/MS. Gyne secretion is typified by butanoate and acetate esters of which decyl-butanoate comprises over 90 %. Butanoates and acetates are also present in workers secretion, but these are of higher MW: octadecyl-butanoate being the major compound. Using synthetic mixtures of gyne and worker Dufour's gland, we have tested the hypothesis that these secretions modify the aggression behaviour of the host species Formica cunicularia. Gyne synthetic mixture significantly reduced the aggression of the host workers towards alien conspecific, while neither pentane nor worker synthetic mixture had this effect. Although gyne Dufour's gland content of the American species P. breviceps was reported to pacify host worker aggression (Topoff et al., 1988), we suggest that it acts as a repellent. For testing this hypothesis we exposed starved host workers to a droplet of honey before and after applying decyl-butanoate (queen major compound), octadecyl-butanoate (worker main compound), limonene (a reported ant repellent), and pentane (solvent control). Of these, the workers were repelled only by decyl-butanoate and did not approach the honey. We conclude that queens rely on cuticular chemical insignificance to enter the nest unnoticed, but also use Dufour's repellents to deter any potential host aggressors.