Wing-Wing Interactions at Low Reynolds Numbers in Whitefly Flight.

At very small scales (∼1 millimeter), flying insects adopt various strategies to accommodate the increased effects of viscosity. One such tiny insect is the tobacco whitefly Bemisia tabaci, which flies using a total of four membranous wings (two forewings and two hindwings). In this study, we examine how aerodynamic interactions among the whitefly's wings influence its aerodynamic performance. To do so, we first created a three-dimensional reconstruction of a whitefly's wing kinematics. Then, we simulated hovering flight using an in-house immersed-boundary-method computational fluid dynamics solver. Using the simulation results, we measured the individual performance of each wing, and we examined the wake structures and vortices generated by flapping. In our analysis, we distinguish between ipsilateral interactions (between the forewing and hindwing) and contralateral interactions (between both pairs of wings as they meet across the body). Our results indicate that both types of wing-wing interactions combine to increase lift by 10.95% and lift-to-power efficiency by 12.83%, compared to the four wings flapping independently. These findings provide insights into how tiny flying insects like the whitefly employ unsteady aerodynamic mechanisms to improve their flight performance at low Reynolds numbers.