In recent years, the use of molecular genetic methods in insect pest studies has become increasingly common, and there is every indication that this trend will continue.  Knowing the distribution of genetic polymorphism not only helps reveal the history of pest populations but also the direction and pattern of their evolution.  The genetic variability of two insects Ceratitis capitata (Wiedemann) (the medfly) and Bactrocera oleae (Gmelin) (the olive fly), harmful pests in the Mediterranean area, was analysed using MLEE and RAPD-PCR.  The validity of these methods for pest population genetic studies was evaluated.  Different levels of variation were detected by the two methods.  In general, olive fly populations were found to be more variable than medfly populations.  The data are discussed in relation to the different life strategies of the two species and their history of expansion.  Identification-diagnostic markers were detected.