Chemical and behavioural studies of the trail-following pheromone in the leaf-cutting ant Atta opaciceps, Borgmeier (Hymenoptera: Formicidae)

• The trail pheromone of Atta opaciceps was analysed.
• A. opaciceps foragers respond more strongly to their own pheromone.
• A. opaciceps foragers follow trails of the venom gland of the heterospecific foragers.
• 2,5-DMP, 3-ethyl-2,5-DMP and M4MPC were identified in the venom gland secretion.
• M4MPC was identified to elicit the trail-following behaviour in A. opaciceps.

To understand the significance of the trail pheromone used in chemical communication of the leaf-cutting ants Atta opaciceps we investigated, under laboratory conditions, the trail-following behaviour of different castes. We observed a clear behavioural discrimination of conspecific venom gland extract of foraging ants from those of other species. Additionally, we determined the pheromone composition of A. opaciceps venom gland secretion using a two-dimensional gas chromatography coupled with mass spectrometry. Chemical analyses revealed the presence of three nitrogen-containing compounds, identified as 2,5-dimethylpyrazine, 3-ethyl-2,5-dimethylpyrazine and methyl 4-methylpyrrole-2-carboxylate (M4MPC). Four different bioassays performed with workers from different castes of A. opaciceps suggested that the trail pheromone elicits the trail-following behaviour in conspecifics of all castes, but the foragers respond more strongly to their own pheromone than to that of other castes (gardeners, generalists and soldiers). In addition, A. opaciceps foragers follow the trails made with the venom gland extracts of the unrelated Acromyrmex subterraneus subterraneus foragers as well as they follow the trails made with their own venom gland extract. M4MPC was identified to be the most abundant and the most behaviourally active component of the venom gland extract of A. opaciceps foragers.

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