More and bigger queens: a clue to the invasive success of the Argentine ant (Hymenoptera: Formicidae) in natural habitats

Abstract

Understanding the invasion process of an exotic species could be useful to manage its dispersion in natural habitats. To that effect, we provide new data on the queens' biological and physiological characteristics in Linepithema humile (MAYR, 1868) colonies from both the invasion front (contact area) and the totally invaded area (invaded area) in order to examine the differences between them. We analyze: 1) queen densities per liter of nest soil, 2) fat content (%), 3) oviposition rates, and 4) the queen / worker thorax volume ratios of individuals from nests situated in the contact and invaded zones. All these parameters are good estimators of the invasive capabilities of colonies, as they are related to dispersion speed and successful colony foundation. Although we did not detect physiological differences in the fat content and oviposition rates of queens from the two zones, we found evidence of differences in the social structure of nests (queen densities) and in the morphology of queens (queen / worker thorax volume ratios) between nests from the invasion's contact and invaded zones. In the former there were bigger queens and higher queen densities than in the latter. Those differences are probably a response to the different ecological contexts of the two zones and would provide the colonies in the contact zone of the invasion with a higher invasiveness potential for competing with the native ant community for empty niches and resources