none Adult parasitic wasps need nectar or some other fragrant food source, but the effect of food odours on their behaviour has not been investigated to any extent. Females of the parasitic wasp Microplitis croceipes learn volatile odours associated with host sites and use them to find hosts more effectively. We have now performed flight tunnel experiments that show that this wasp also uses airborne odours to find food sources. Females learn associatively and subsequently fly to volatile odours presented for smell while they are feeding on sugar water. Furthermore, they can learn two novel odours associated with separate host and food resources and then make an accurate choice between these odours on the basis of their relative host and food needs. This ability of parasitic wasps to link different odours with specific resources and then effectively to use them as cues for choice between competing needs is of fundamental and applied importance.