Studies on the sensory sensilla on the tarsi and external genitalia of the Asian tiger mosquito, Aedes albopictus (Skuse)

Dengue fever is a worldwide health problem transmitted mainly by Aedes albopictus. The ability of female mosquitoes to transmit disease depends on their behavioral responses to locate their host. The presence of different types of sensory sensilla with different morphological characteristics is the most distinctive feature of Ae. albopictus, in addition to the main sensory organs. The sensory sensilla are chemosensory contacts that Ae. albopictus uses to locate long-distance hosts and oviposition sites by receiving well-defined cues such as changes in temperature and humidity, mechanical impact, and odors. As a result, it is crucial to study the sensory sensilla of Ae. albopictus. Although the sensory sensilla of Ae. aegypti have been extensively studied, but there is still a lack of knowledge about the sensory sensilla of the Asian tiger mosquito, Ae. albopictus. This study aimed to investigate the different types of sensory sensilla on the tarsi and external genitalia of both sexes of Ae. albopictus and their morphological features using a scanning electron microscope. The results demonstrated that the tarsi have five types of sensory sensilla: sensilla chaetica, grooved pegs, sensilla campaniform, sensilla basiconica, and sensilla coeloconica. There are two thick, grooved sensilla on the tarsal joints. Sensilla coeloconica on the tarsus are hidden under scales in a raised pit and have a diameter of 13.69 +/- 0.071 mu m, which is significantly larger than those on the external genitalia of males, which have a diameter of 7.65 +/- 0.065 mu m. Sensilla coeloconica is absent from the external genitalia of females. Two types of senillae chaetica are found on the tarsomeres, near the claws, and on the joints, which differ significantly in morphology and morphometric parameters. The ovulation-supporting cerci are provided with three pairs of long sensilla chaetica at the apex, measuring 111.36 +/- 0.020 mu m in length. Two groups of four apical sensilla and short spiny subapical sensilla are randomly distributed on the ovipositor. The female external genitalia have two types of sensilla chaetica, which are arranged in rows and are significantly smaller than those of the male external genitalia.