Olfactory responses of the leaf-cutting ants Atta cephalotes (L.) and Acromyrmex octospinosus (Reich) (Hymenoptera: Formicidae) in the laboratory

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Abstract
The leaf-cutting ants Atta cephalotes (L.) and Acromyrmex octospinosus (Reich) were tested in a moving-air olfactometer for their responses to a variety of odours from leaves, fruit, flowers, essential oils, other ants and a fungus garden. The line of a foraging trail established in still air tended to loop downwind in the presence of a laminar air flow. The ants exhibited positive, negative and neutral responses to the test odours, confirming the existence of attractants and repellents in substrate materials. Neutral responses to the odours of several of the materials that were acceptable for cutting showed that arrestive materials were not necessarily attractive. Ants orientating towards the source of an odour often secreted a pheromone trail. Atta and Acromyrmex responded differently to several of the materials tested, and the responses to odours of young and old leaves were not totally consistent with the observed cutting preferences. Removal of wax from non-attractive leaves made them attractive. Both species responded negatively to lemon-oil odour, but some Acromyrmex workers showed a hostile response. A hostile response was also elicited by the odour from other ants. Fungus-garden odour elicited a positive investigatory response, and no response was shown to queen odour. Laden Atta workers did not respond to an odour that was attractive to unladen ants, and laden examples of Acromyrmex responded in small numbers to such odours. The addition of attractive chemicals to baits for the control of leaf-cutting ants would improve pick-up by making the bait particle easier to find.