Consequences of chronic ingestion of a selenium-contaminated diet on the Argentine ant, Linepithema humile

Selenium (Se) is a metalloid that occurs naturally from the weathering of Cretaceous shale, but can also be mobilized as a result of human activities such as irrigation. It has gained attention for its role as both an essential element and a toxicant to humans and animals. However, there is comparatively less evidence available for the effects of Se on arthropods. Interestingly, some plants are adapted to survive in Se-rich soils and concentrate Se in structures frequently consumed by ants, such as the pollen, nectar and seeds. The invasive Argentine ant, Linepithema humile, known for its affinity to sugar rich diets, was used as a model to investigate the consequences of chronic exposure to Se in the diet.  To compare the impact of four environmentally common forms of Se on mortality and accumulation in worker ants, we conducted non–choice feeding assays. Ant tissue was analyzed for Se using hydride atomic absorption spectroscopy. Choice tests were used to determine whether Se might act as a deterrent to ant feeding. Results indicated that methylselenocysteine was the most toxic among the four forms tested.  Ants feeding on the two least toxic forms (selenomethionine and selenite) accumulated the highest levels of Se. Analysis also revealed that Se was not repellant to ants, regardless of the background sucrose concentration. These findings suggest possible detrimental implications for both ant colonies and their predators in contaminated habitats.  Future work is needed to investigate the impact of sub-lethal levels Se on ant development and fecundity.