Function of the dendritic setae in Aedes aegypti mosquito pupae: float hairs don't float

Methods: Using Aedes aegypti , we checked to see whether the dendritic setae are hydrophilic and tested the behavioral effects of their removal. In a preliminary closed-system experiment, a pupa was placed in water in a test tube and a syringe attached in continuity with the air space above the water. When pressure was increased by depressing the plunger, a pupa responded by swimming toward the surface. When negative pressure was applied by lifting the plunger, a pupa actively dove. Using a more sophisticated apparatus with a pressure transducer, we tested the effects of dendritic setae removal on behavior in response to pressure changes. Results: The cuticular surface of the dendritic setae is hydrophilic. No significant differences were found in pupae with or without the dendritic setae relative to dive duration, applied pressure duration, or maximum pressure applied, but response time to pressure change in pupae (males and females) without the setae was significantly increased. Conclusion: Hydrophilic dendritic seta cuticle is consistent with our hypothesis but not with a floatation function. Ablation experiments supported our hypothesis that the dendritic setae are involved with buoyancy sensing by bending in response to directional water currents.