The study of parasitoid reproductive behaviour is crucial to understanding how parasitoids influence host population dynamics, and the strategies used by parasitoids to maximize their reproductive success. Studying how the parasitoid optimizes its reproductive resources is important as it provides information to improve the efficiency of a biological control programme. Many studies have been carried out on Aphidius ervi to assess the foraging behaviour of the parasitoid, but how the age of the parasitoid affects its foraging behaviour is still poorly understood. In the present study, the influence of the time elapsed between adult parasitoid emergence and the first oviposition in A. ervi was evaluated. Correlations between the parasitoid size and other fitness components were also investigated. Our results show how the parasitoid senescence is associated with the loss of reproductive capacity, as the late field release of parasitoids reduces their total parasitism. We also observed a parasitization rhythm independent of the parasitoid age. Possible explanations for the observed phenomena are discussed.