J Vector Borne Dis 44, December 2007, pp. 245–249 Morphological method for sexing anopheline larvae S.N. Emami a , H. Vatandoost a , M.A. Oshaghi a , F. Mohtarami a , E. Javadian a & A. Raeisi b a Department of Medical Entomology & Vector Control, School of Public Health & Institute of Health Research, Medical Sciences/Tehran University, Tehran; b Malaria Department, Ministry of Health & Medical Education, Tehran, Iran Abstract Background & objectives: Most of autocidal control of malaria vectors relies on the rearing and release of large numbers of sterile male into a wild population and it would be crucial to separate the males from females before release. This could result in enormous economic benefits in the mass rearing and raise the efficiency of the field operations. The development of genetic sexing of mosquitoes, enabling the release of males only, but impairing the overall fitness of the released insect has been considered greatly. Here we report on a morphological sexing method for the preferential diagnosis and separation of males in late III and IV instar larvae for the mosquitoes Anopheles stephensi Liston and An. culicifacies s.l. (Diptera: Culicidae), the principal vectors of human malaria in Asia and Indian subcontinent. Methods: Male mosquitoes are identified by their tube like organ at the 9th abdomen segment which originates from segment parallel to the spiracles. Length and width of this organ is measured as 66.66 ± 9.5 and 14.3 ± 1.5 μm respectively. The whole length of the organ is 201.63 ± 23.4 μm. Two fried eggs in the anterior portion of the segment are apparent in males. The length of tube in female is shorter than the male (almost half of the length–37.95 ± 4.0 μm), its width is slightly stout and wider than the male (16.72 ± 1.4 μm). Two fried eggs in the anterior portion of the segment are absent. After separation of live male larvae by those characteristics, they were transferred into the trays and emerged adults were identified to ascertain correct identification of sex. Results: All the larvae with male organs developed into male adults with hairy antennae and club shaped palpi, whereas all the female larvae developed into adult females. Interpretation & conclusion: The sex separation at the larval stage will provide a clue for embryonic origin of sex organs, insecticide selection at the larval stage, sex related genes, male sterility and other measures. Key words Anopheles larvae – malaria – sex determination Introduction The sterile insect technique (SIT) is currently being used for the control of some medical and agricultural pests. The SIT relies on the rearing and release of large numbers of genetically sterile insects into a wild population. In many applications of autocidal control, it would be efficient to separate the males and females before release 1 . Avoiding assortative mating and any increase in the size of the natural population, and elimination of females which may be disease vectors or which cause damage to produce or livestock are