Yeast biota of the red imported fire ant

Abstract

Few researchers have addressed the relationship between the Solenopsis complex and its internal microbiota. Most investigations on the red imported fire ant (Solenopsis invicta) are either control oriented or emphasize the species' negative impact on ecosystems. The objectives of this study were to isolate and identify yeasts from the red imported fire ant and to determine the impact of associated yeasts on colony vigour. Colonies were collected from five locations in Texas that represent a transect along a decreasing moisture gradient from the southeastern to the northwestern region of the state. Colonies were collected during winter of 1992, and the spring, summer, and autumn months of 1993. Physiological and morphological tests showed that the 327 yeast isolates from worker haemolymph represent five yeast species: Candida parapsilosis, Candida lipolytica, Candida guillermondii, Candida rugosa, and Debaryomyces hansenii var. hansenii. The biomass of red imported fire ant colonies with yeasts was significantly greater than ant colonies without yeasts during winter and spring months. Moreover, 80% of the fourth-instar larvae collected during the autumn months harboured yeasts. These data indicate that the presence of yeast does not reduce colony biomass. A high prevalence of yeasts in larvae suggests a nutritional role and that this association is not random.