Mosquitoes modulate leg dynamics at takeoff to accommodate surface roughness

Abstract

Insects perform takeoffs from a nearly unquantifiable number of surface permutations and many use their legs to initiate upward movement prior to the onset of wingbeats, including the mosquito. In this study we examine the unprovoked pre-takeoff mechanics of Aedes aegypti mosquitoes from two surfaces of contrasting roughness, one with roughness similar to polished glass and the other comparable to the human forearm. Using high-speed videography, we find mosquitos exhibit two distinct leg actions prior to takeoff, the widely observed push and a previously undocumented leg-strike, where one of the rearmost legs is raised and strikes the ground. Across 106 takeoff sequences we observe a greater incidence of leg-strikes from the smoother surface, and rationalize this observation by comparing the characteristic size of surface features on the mosquito tarsi and each test surface. Measurements of pre-takeoff kinematics reveal both strategies remain under the mechanosensory detection threshold of mammalian hair and produce nearly identical vertical body velocities. Lastly, we develop a model that explicates the measured leg velocity of striking legs utilized by mosquitoes, 0.59 m s −1 .

Landing mosquitoes bounce when engaging a substrate

“…While the timescale over which landings occur is rapid, it is comparable to the timescale of takeoff 2 and lengthy compared to the timescale of a single wingbeat 56 . Thus, it is possible leg compression at landing is not wholly passive.…”

“…Mosquitoes are anesthetized with CO for placement into the flight arena, and given sufficient time to recover from anesthetization before filming. To encourage resting mosquitoes into flight, the arena is vibrated at low amplitude 25 Hz for up to 5 s. Vibration does not catapult mosquitoes from walls and mosquitoes are given at least 1 s ( wingbeats) 2 to recover flight before a landing is considered for analysis. The landing surface protrudes through the walls of the arena and is supported externally such that it does not vibrate with the arena walls.…”

Malaria mosquitoes use leg push‐off forces to control body pitch during take‐off

“…Comparing the contribution of aerodynamic torques and leg push-off torques to the pitch-up movement within the push-off phase (Figure 5e) shows that the positive contribution of During take-off, a mosquito has to produce high-enough forces to reach an escape velocity that maximizes the chance to escape a predator or a defensive blood host (Roitberg et al, 2003). These forces are generated by a combination of the aerodynamic forces produced by the flapping wings and ground push-off forces from the legs (Muijres et al, 2017;Smith et al, 2018). In our simulations, we compared the required forces needed to perform the measured take-off with the aerodynamic forces generated by the wings.…”

“…Finally, many insects combine leg forces with aerodynamic forces to generate the upward acceleration, for example, the voluntary take-off of the fruit fly (Chen & Sun, 2014;Card & Dickinson, 2008). It has been suggested that mosquitoes avoid tactile detection by extending their legs while generating aerodynamic forces with their wings (Muijres et al, 2017;Smith, Clayton, Khan, & Dickerson, 2018), keeping the force on the substrate lower than the tactile detection threshold of mammalian skin (F threshold = 0.07 mN; Li et al, 2011). This may explain why the difference between a voluntary take-off and escape take-off in the fruit fly is not found in mosquitoes (Muijres et al, 2017).…”

Remote radio control of insect flight reveals why beetles lift their legs in flight while other insects tightly fold

“…For development of such micro air vehicles, it is necessary to reveal the mechanisms of insect flight and understand their unique movements. For example, mosquitoes use the movement of two different legs depending on the surface roughness during takeoff [5]. A bioinspired robot with a similar mechanism was then developed for the purpose of taking off from surfaces of different roughness [6].…”