Journal of Vector Borne Diseases (Dec 2007)
Morphological method for sexing anopheline larvae
Abstract
Background & objectives: Most of autocidal control of malaria vectors relies on the rearing andrelease of large numbers of sterile male into a wild population and it would be crucial to separate themales from females before release. This could result in enormous economic benefits in the massrearing and raise the efficiency of the field operations. The development of genetic sexing ofmosquitoes, enabling the release of males only, but impairing the overall fitness of the releasedinsect has been considered greatly. Here we report on a morphological sexing method for thepreferential diagnosis and separation of males in late III and IV instar larvae for the mosquitoesAnopheles stephensi Liston and An. culicifacies s.l. (Diptera: Culicidae), the principal vectors ofhuman malaria in Asia and Indian subcontinent.Methods: Male mosquitoes are identified by their tube like organ at the 9th abdomen segment whichoriginates from segment parallel to the spiracles. Length and width of this organ is measured as66.66 ± 9.5 and 14.3 ± 1.5 μm respectively. The whole length of the organ is 201.63 ± 23.4 μm. Twofried eggs in the anterior portion of the segment are apparent in males. The length of tube in femaleis shorter than the male (almost half of the length–37.95 ± 4.0 μm), its width is slightly stout andwider than the male (16.72 ± 1.4 μm). Two fried eggs in the anterior portion of the segment areabsent. After separation of live male larvae by those characteristics, they were transferred into thetrays 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 clubshaped palpi, whereas all the female larvae developed into adult females.Interpretation & conclusion: The sex separation at the larval stage will provide a clue for embryonicorigin of sex organs, insecticide selection at the larval stage, sex related genes, male sterility andother measures.
