In insect societies the presence of several reproductive individuals into a colony can generate conflict over reproduction. For example, in polygynous ant societies, the presence of several mated queens inside the nests can lead to a decrease in their individual oviposition rate as a result of queen-queen competition. In the Argentine ant (Linepithema humile (Mayr, 1898), a highly polygynous ant species, nestmate queens differed in their oviposition rates and ovarian activity: we discovered that there were clearly high- and low-fecundity queens inside the nests. However, when queens were placed in monogynous conditions, these differences disappeared. Taken together, these results provide strong evidence for the existence of reproductive inhibition among nestmate queens in this invasive ant species. Our results also underscore differences in the cuticular hydrocarbon profiles of high- and low-fecundity queens under polygynous conditions. These differences were mainly related to three compounds correlated with fecundity and queen survival, the di-methyl alkanes 5,11-diMeC₂₉, 5,11-diMeC₃₁ and 5,11-diMeC₃₃, suggesting their potential role as multifunctional pheromones. To our knowledge, this is the first study to experimentally examine the proximate mechanisms underlying reproductive differences among Argentine ant queens under polygynous conditions using an approach that combines physiological, behavioural, and chemical data. Our study improves our general understanding of the factors that regulate and maintain highly polygynous insect societies.

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