The labrum and labral sensilla of mosquitoes (Diptera: Culicidae): a scanning electron microscope study

Labra of both sexes of 40 species of mosquitoes of 15 genera were examined using scanning electron microscopy, and 8 of these species using light microscopy, to investigate whether structural differences exist between labra of blood-sucking and non-blood-sucking mosquitoes. Three groups of sensilla are present in the apical region of labra of blood-sucking females: the apical sensilla, two uniporous sensilla; the subapical sensilla, two more uniporous sensilla; and further subapically, two campaniform sensilla. Only campaniform sensilla are found on labra of male mosquitoes. Labral sensilla are absent in the two Toxorhynchites species examined. Females of these two species are not known to feed on blood. The presence of apical sensilla and subapical sensilla appear to be related to blood-sucking habits of mosquitoes. These sensilla probably function in blood detection during feeding. Campaniform sensilla probably function as flow receptors. Cuticular microsculpture in various forms present on the dorsal wall of the labrum in the female suggests the presence of resilin in the wall of the labrum.