The use of cover crops can promote the abundance and early arrival of populations of natural enemies. Cereal cover crops between orchards rows could encourage the early arrival of the parasitoidAphidius platensis, as they offer alternative winter hosts (e.g.,Rhopalosiphum padi), enhancing the control ofMyzus persicaein spring. However, the preference for and suitability of the alternative host must be addressed beforehand. To evaluate the potential of this strategy, we assessed host preference using behavioural choice tests, as well as no-choice tests measuring fitness traits, when developing on both host species. One source field for each aphid population from the above hosts was chosen. There was a clear choice forR. padicompared toM persicae, independently of the source, probably due to more defensive behaviours ofM. persicae(i.e., kicks and escapes). Nevertheless, both aphid species were suitable for parasitoids' development. The female progeny developed onR. padiwere larger in size, irrespective of their origin. According to our results, in peach orchards with cereals sown between peach trees during the autumn, where we expect whenR. padipopulations will no longer be available during spring,A. platensisshould be able to switch toM. persicae.