Sub-lethal doses of imidacloprid alter food selection in the invasive garden ant Lasius neglectus.

Despite several restrictions to their use, neonicotinoid insecticides are still widely employed worldwide. Residual sub-lethal amounts of these chemicals can have detrimental effects on the behavior of non-target insects. Toxic effects on economically important species such as bees have been widely documented, but less is known about their toxic action on other social insects, such as ants. In this study, we assessed the effect of different sub-lethal doses of the neonicotinoid imidacloprid on the ability of colonies of the invasive ant Lasius neglectus to select the most profitable resource. We used Y-shaped mazes having an imidacloprid-polluted or an unpolluted sucrose solution on the two branches. Two sucrose (0.1 M, 0.5 M) and two imidacloprid (1 µg/ml, 10 µg/ml) concentrations were used. In parallel, we evaluated the marking activity of foragers who fed on the same solutions. We found that the 0.1 M sugar solution polluted with 1 µg/ml imidacloprid was significantly more frequently selected in binary choices experiments than the unpolluted resource. Moreover, the ingestion of the same combination of sugar and imidacloprid significantly increased the marking rate of foragers. The higher concentration of the pollutant had lower effects, probably because of the hormesis phenomenon. Results suggest that the lower sub-lethal dose of imidacloprid can lead ants to select again the polluted resource. This "active" selection of the pollutant may magnify the negative effects on the colonies. Due to their ecological role, any impairment of ant survival or behavior may have detrimental cascade effects on the whole ecosystem.

Local environmental variables are key drivers of ant taxonomic and functional beta-diversity in a Mediterranean dryland.

The decomposition of beta-diversity (ß-diversity) into its replacement (ßrepl) and richness (ßrich) components in combination with a taxonomic and functional approach, may help to identify processes driving community composition along environmental gradients. We aimed to understand which abiotic and spatial variables influence ant ß-diversity and identify which processes may drive ant ß-diversity patterns in Mediterranean drylands by measuring the percentage of variation in ant taxonomic and functional ß-diversity explained by local environmental, regional climatic and spatial variables. We found that taxonomic and functional replacement (ßrepl) primarily drove patterns in overall ß-diversity (ßtot). Variation partitioning analysis showed that respectively 16.8%, 12.9% and 21.6% of taxonomic ßtot, ßrepl and ßrich variation were mainly explained by local environmental variables. Local environmental variables were also the main determinants of functional ß-diversity, explaining 20.4%, 17.9% and 23.2% of ßtot, ßrepl and ßrich variation, respectively. Findings suggest that niche-based processes drive changes in ant ß-diversity, as local environmental variables may act as environmental filters on species and trait composition. While we found that local environmental variables were important predictors of ant ß-diversity, further analysis should address the contribution of other mechanisms, e.g. competitive exclusion and resource partitioning, on ant ß-diversity.

Small-scale drivers on plant and ant diversity in a grassland habitat through a multifaceted approach.

Semi-natural grasslands are characterized by high biodiversity and require multifaceted approaches to monitor their biodiversity. Moreover, grasslands comprise a multitude of microhabitats, making the scale of investigation of fundamental importance. Despite their wide distribution, grasslands are highly threatened and are considered of high conservation priority by Directive no. 92/43/EEC. Here, we investigate the effects of small-scale ecological differences between two ecosites present within the EU habitat of Community Interest of semi-natural dry grasslands on calcareous substrates (6210 according to Dir. 92/43/EEC) occurring on a Mediterranean mountain. We measured taxonomic and functional diversity of plant and ant communities, evaluating the differences among the two ecosites, how these differences are influenced by the environment and whether vegetation affects composition of the ant community. Our results show that taxonomic and functional diversity of plant and ant communities are influenced by the environment. While vegetation has no effect on ant communities, we found plant and ant community composition differed across the two ecosites, filtering ant and plant species according to their functional traits, even at a small spatial scale. Our findings imply that small-scale monitoring is needed to effectively conserve priority habitats, especially for those that comprise multiple microhabitats.

Palatability of glyphosate in ants: a field experiment reveals broad acceptance of highly polluted solutions in a Mediterranean ant.

Glyphosate is a systemic herbicide still used in many countries, though there are several known detrimental effects on animals. Previous studies concerning its effects on social insects are available, but they are primarily focused on honeybees; little is known about the interactions of this compound with ants. Here, we assessed whether different concentrations of glyphosate can be perceived by ant workers and to what extent. As a model species, we used the Mediterranean ant Crematogaster scutellaris, commonly found in agroecosystems. We performed 3000 individual tests of acceptance using ten different solutions of various concentrations of the herbicide. Half of the solutions contained added sucrose in order to test the possible masking effect of the sugar taste on glyphosate. We used comparable glyphosate concentrations to those previously used in other studies on social insects or suggested by the producer. We found that the acceptance of the solutions decreased as the concentration of the herbicide increased. However, a significant percentage of ants drank the solutions with concentrations up to dozens of times higher than those inducing toxic effects in bees. In light of these results, we urge further assessment of the effects of glyphosate on ants, particularly because the food ingested by workers is transferred to the brood and queens, posing a potential threat to the health of the entire colony. Surprisingly, we did not record any difference in acceptance between solutions with and without sugar; this point is discussed regarding drought stress.