While several genetic and transgenic approaches have been developed that permit male-female separation for some species, separation based on sexual size dimorphism continue to be a useful technique in the laboratory and in small factory settings for elimination of females. In general, female mosquitoes of many species such as Aedes and Culex but also Anopheles quadrimaculatus and A. albimanus are larger than males in the pupae stage. Vienna Scientific Instruments developed a sieve-based sex separator for the FAO/ IAEA Insect Pest Control Laboratories. The mechanical sex separator consists of an acrylic tube as main body in which a tray with pupae can be inserted. The constructed tray not only simplifies pupae insertion but also removes air bubbles. Several sieves of various sizes can be inserted and removed with a detachable handle. The sieves allow male adults only to fly to a higher different compartment from where they can be removed.