Mosquito repellence induced by tarsal contact with hydrophobic liquids

Abstract

Mosquito legs have a unique highly water-repellent surface structure. While being beneficial to mosquitoes, the water-repellence of the tarsi enhances the wettability of hydrophobic substances such as oils. This high wettability induces strong attraction forces on a mosquito's legs (up to 87% of the mosquito's weight) towards the oil. We studied the landing behaviour of mosquitoes on oilcoated surfaces and observed that the mosquito contact time was reduced compared to that on hydrophilic-liquid-coated surfaces, suggesting that the oil coating induces an escape response. The observed escape behaviour occurred consistently with several hydrophobic liquids, including silicone oil, which is used globally in personal care products. As the repellent effect is similar to multiple hydrophobic substances, it is likely to be mechanically stimulated owing to the physical properties of the hydrophobic liquids and not due to chemical interactions. On human skin, the contact time was sufficiently short to prevent mosquitoes from starting to blood-feed. The secretion of Hippopotamus amphibius, which has physical properties similar to those of low-viscosity silicone oil, also triggered an escape response, suggesting that it acts as a natural mosquito repellent. Our results are beneficial to develop new, safe, and effective mosquito-repellent technologies.

Aquatain® Causes Anti-Oviposition, Egg Retention, Oocyte Melanization and Triggers Female Death in Ae. Aegypti

“…First, reducing the water surface tension in the AMF-treated containers, particularly in the AMF-based no-choice and three-fourths treatments, may have produced strong, attractive capillary forces that dragged the legs of females towards the water, consequently increasing the likelihood of sinking and death. In support of this assertion, on the water surface, but not on the water surface with a silicone oil lm, female mosquitoes can use the surface as a foothold to lay their eggs, using a maximal repulsive force from their legs [59]. Second, the untimely internal oocyte melanogenesis during egg retention may have occasioned the production and accumulation of toxic compounds among females with increased exposure to AMF-treated water, which elevated the possibility of intoxication.…”

“…The mechanism by which this phenomenon occurs has been well documented. According to Likura et al [59], mosquito legs are highly hydrophobic, and this trait causes a weight-supporting force on water surfaces. For a successful egg-laying to occur, a gravid female must generate a repulsive force from to legs to be able to use the surface of the water as a foothold [58,59] and evaluate its quality [20].…”

“…According to Likura et al [59], mosquito legs are highly hydrophobic, and this trait causes a weight-supporting force on water surfaces. For a successful egg-laying to occur, a gravid female must generate a repulsive force from to legs to be able to use the surface of the water as a foothold [58,59] and evaluate its quality [20]. However, when silicone oil is added over the water surface, it generates an attractive capillary force that drags legs towards the water [58], inducing a short contact time and an escape response [59].…”

“…For a successful egg-laying to occur, a gravid female must generate a repulsive force from to legs to be able to use the surface of the water as a foothold [58,59] and evaluate its quality [20]. However, when silicone oil is added over the water surface, it generates an attractive capillary force that drags legs towards the water [58], inducing a short contact time and an escape response [59]. A shortened contact time and startle will result in an incomplete exploration of the quality of the oviposition site and thus a decreased probability of egg deposition.…”

Aquatain® causes anti-oviposition, egg retention and oocyte melanization and triggers female death in Aedes aegypti

“…The mechanism by which this behavioral change is effected has been well documented. According to Likura et al [ 59 ], mosquito legs are highly hydrophobic, causing a weight-supporting force on water surfaces. For a successful egg-laying to occur, a gravid female must generate a repulsive force from the legs to be able to use the surface of the water as a foothold [ 58 , 59 ] and evaluate its quality [ 20 ].…”