Mabel GUERRA, Eduardo FUENTES-CONTRERAS, Hermann M. NIEMEYER
Departamento de Ciencias Ecológicas, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago, Chile

Some aphid species parasitised by a primary parasitoid exhibit changes in their behaviour suggesting an aphid adaptive suicide to avoid successful parasitoid development. On the other hand, primary parasitoids at their larval stage modify the aphid behaviour in their own benefit when the aphid is close to mummy formation Thus, parasitised aphids containing a non-diapausing parasitoid leave the colony to mummify in the upper side of the leaves decreasing hyperparasitoid attack.

In order to evaluate if the above mentioned aphid responses are influenced by volatile compounds, we document the olfactometric behaviour of S. avenae parasitised by Aphidius ervi at larval and prepupal stage (close to mummification). associated with volatiles from a colony of healthy S. avenaeand virgin females of the hyperparasitoid Allaxvsta victrix. 6-Methyl-5-hepten-2-one, previously reported as spacing and sexual pheromone of A. victrix, and thus probably related with the response of parasitised aphids to hyperparasitoid odours, was also tested to evaluate its effect.