Abstract

The behavioural response of an aphid-tending ant, the Argentine ant Linepitherma humile, to semiochemicals related with spacing behaviour in the aphid Rhopalosiphum padi (L.) was used evaluated. The compounds involved were 6-methyl-5-hepten-2-one (MHO), 6-methyl-5-hepten-2-ol (MHOH), and 2-tridecanone (2-T). Hexane solutions of these semiochemicals either singly or mixed, and extracts obtained by trapping volatile compounds from wheat seedlings either alone or infested with two different densities of aphids were used as stimuli in olgactometric bioassays. Ants showed attraction to volatile extracts from plants infested at both densities, and slightly preferred volatile compounds from lightly over heavily infested plants in a choice tests. On the other hand, while a dose-dependent repellence response was elicited by the naturally-occurring mixture of MHO, MHOH and 2-T, single compounds did not elicit significant responses in olfactometric bioassays. The function of these semiochemicals as indicators of quality of the aphid colonies as trophic resource to ants in discussed.