Figure 3.

Predictions of the normalized densities of airborne aphids in a convective boundary layer with wind shear (u_*=0.3 m s⁻¹ and w_*=2.0 m s⁻¹) (filled circles) and boundary layer with intermediate stability (u_*=0.4 m s⁻¹ and w_*=1.0 m s⁻¹) (open circles). Aphids are assumed to take off at random times, ascend continually to an altitude of 100 m and then cease flapping unless they come within 10 m of the ground whereupon they ascend once again to an altitude of 100 m and the cycle repeats. The aphids have a fall speed of −1 m s⁻¹ in still air and most aphids complete several cycles within 1 hour. This model plainly does not fit the log density/log height relationship found in the observed aphid density profiles.