Dual functions of insect wings in an odor-guided aeronautic navigation.

Insects can detect and locate distant odor sources (food, mate, etc.) by tracking odor plumes, which is key to their survival. During an odor-guided navigation, flapping wings have been speculated to actively draw odorants to the antennae and enhance olfactory sensitivity. Utilizing an in-house computational fluid dynamics solver, we have quantified the odor plume structures of a fruit fly in a forward flight motion and have confirmed that the flapping wings induce a strong vortex flow over the insect's head, thereby enhancing the odor mass flux around the antennae (by ~1.8 times). To further understand the function of different wing area in terms of aerodynamics and olfaction, we designed an altered fruit fly wing by removing its trailing-edge portion; subsequent simulations showed that this altered wing has an improved lift production but with significantly reduction of the induced odor mass flux. Contrary to the common belief that the wing shapes of an insect are optimized only for aerodynamic performance, our results suggest that, because both aerodynamic and olfactory functions are indispensable during the odor-guided navigation, insects may sacrifice some aerodynamic potential to enhance olfactory detection; and the shape and size of the wing may be a balance between the two functions. Furthermore, we found that higher wing beat frequency and wing reversal phase induce higher odor mass flux, while lower beat frequency and downstroke phase produce better lift coefficient, which indicates another balance between the two functions.