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 oil-coated 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.
Highlights
Aquatic pupa to fly away from the surface (Supplementary Video S1)
The low-viscosity PDMS (L-PDMS) and squalane contact angles were much smaller than 90°, indicating that the hydrophobic mosquito legs have a high wettability to hydrophobic liquids (Supplementary Table S2)
In order to evaluate the wettability of L-PDMS on the mosquito legs, we determined the critical surface tension of the mosquito legs by using the results of the contact angle measurements, because surface tension is an indicator of wettability
Summary
Aquatic pupa to fly away from the surface (Supplementary Video S1). While the roughness of hydrophobic surfaces magnifies their non-wetting property with respect to water, it enhances their wettability with respect to hydrophobic liquids[15]. In comparison with a smooth surface, a hydrophobic rough surface is more susceptible to the adhesion of hydrophobic liquids, such as silicone oil and hydrocarbon-based oil This induces a non-negligible attractive capillary force that will pull the surface of mosquito legs towards the liquid, which can have a significant impact on mosquito behaviour. We measured the contact time of mosquitoes on substrates coated with different substances, and observed an escape response on oil-coated surfaces characterised by a short contact time If this escape behaviour occurs consistently with different hydrophobic liquids, it could act an additional mosquito repellent mechanism. We focused on the physical properties of the liquids such as surface tension and viscosity by comparing the wetting and mosquito contact time with medium- and high-viscosity polydimethylsiloxane (M-PDMS and H-PDMS, respectively) to that with L-PDMS. We examined the wettability of the hippopotamus secretion on mosquito legs and assessed whether a substrate coated with this exudate affects mosquito behaviour
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