A computer simulation study of the host instar preference of aphidiids for oviposition and the impact of these parasites on their host aphid populations was performed with a simulation model of experimental mixed, population of Hyperomyzus lactucae-Aphidius sonchi. By varying the relevant population parameters, inital population density and structure as well as temperature, the effect of the characteristics of host instar preference of the parasite for oviposititon on the aphid was investigated. In addition...