Flight Performance and Flight in Wind in Three Phylogenetically Distinct Miniature Insects.

Small size imposes constraints on flight due to a reduction in aerodynamic efficiency of small wings. Consequently, miniature insects are often considered to be poor flyers that disperse by drifting in winds. Only few studies have actually measured the active flight of very small insects. The few that did, report surprisingly high flight speeds compared to the size of such small creatures. To test both the limits to flight performance and response to wind, we tracked free-flight within a wind tunnel in a whitefly, a thrips, and a bark beetle. The studied species represent small insects from three different orders (Hemiptera, Thysanoptera and Coleoptera) that underwent independent miniaturization in the course of evolution. Flights were tracked with and without wind and the wind was either horizontal or vertical. From the 3D flight trajectories of the insects, we extracted aerial velocity and manoeuvring performance. The insects did not passively drift downwind and two of the three insects studied displayed distinct upwind flight behaviors. Maximal flight speed was slower than that of larger insects, but faster in terms of body length per second. The manoeuvrability of two out of the three studied species exceeded that of larger animals in terms of flight speed for a minimal turning radius. These findings advocate the inclusion of active flight in small insect dispersal models and suggest that miniaturization may result in improved aerial manoeuvrability.