Effects of oil-film layer and surfactant on the siphonal respiration and survivorship in the fourth instar larvae of Aedes togoi mosquito in laboratory conditions.

Mosquitoes transmit various diseases; thus, controlling them is necessary to prevent mosquito-borne infections. Unlike flying adult mosquitoes, those in the immature stages are easy to control because of being restricted to their habitats found in an aquatic environment. In this study, we aimed to evaluate of respiration and survivorship in the larvae of Aedes togoi. The mechanism of actions of the oil-film layer and the surfactant as well as their effects on the siphonal respiration of submerged Aedes togoi larvae were analyzed by checking the survival time of mosquito larvae against oil-film layer and surfactant, and conducting experiments using a siphon-model. Compared with an impermeable membrane used for reference (762.4 min; average time in all cases), the survival time of mosquito larvae was 5% longer for the oil-film layer (808.1 min) and 40% longer for the surfactant (1086.9 min). The surface of the siphon was changed from hydrophobic to hydrophilic by addition of a surfactant. In addition, the surface tension and wettability have a significant influence on the opening and closing of siphon. This study would be helpful for understanding the basic mechanism of physical control measures for disturbing the siphonal respiration of mosquito larvae in a way of dissolved oxygen and surface tension. The present results would guide the establishment of effective control measures for mosquitoes.