The role of brood cuticular hydrocarbons in brood recognition by the Argentine ant (Linepithema humile)

As a part of a social community, ant workers must be able to identify juveniles or brood to provide care for them. It has been proposed that ant brood produce a 'brood pheromone', a chemical or combination of chemicals that elicit a brood-specific behavioral response in workers. Knowing that cuticular hydrocarbons (CHCs) are commonly used for species and nestmate recognition, it is possible the cuticular hydrocarbons are also involved in brood recognition. Using gas chromatography-mass spectrometry we investigated differences between CHC profiles of brood and workers of the Argentine ant, Linepithema humile. We found that larvae and pupae have a greater relative abundance of 3-methyl branched alkanes, as well as 5-methyl branched alkanes. To test the bioactivity of these branched hydrocarbons, we used filter papers treated with control substances, hexane extracts of brood, or synthetic hydrocarbons in both a typical Petri dish assay and in a novel flooding assay. In both types of assays, ants regularly antennated and carried papers treated with brood extract. However, neither synthetic 3-methyl C27, nor a mixture of 5-methyl C29 and 5-me C31 induced a carrying response in workers. Although we have not yet definitively identified the brood pheromone, we know it is hexane soluble, and we have developed a novel flooding assay that can be used to elicit brood-specific behavior in Argentine ants. Our findings suggest that workers may use a combination of non-polar compounds, including hydrocarbons, to identify ant brood.