Aphid aerial density profiles are consistent with turbulent advection amplifying flight behaviours: abandoning the epithet 'passive'.
Seminal field studies led by C. G. Johnson in the 1940s and 1950s showed that aphid aerial density diminishes with height above the ground such that the linear regression coefficient, b, of log density on log height provides a single-parameter characterization of the vertical density profile. This coefficient decreases with increasing atmospheric stability, ranging from -0.27 for a fully convective boundary layer to -2.01 for a stable boundary layer. We combined a well-established Lagrangian stochastic model of atmospheric dispersal with simple models of aphid behaviour in order to account for the range of aerial density profiles. We show that these density distributions are consistent with the aphids producing just enough lift to become neutrally buoyant when they are in updraughts and ceasing to produce lift when they are in downdraughts. This active flight behaviour in a weak flier is thus distinctly different from the aerial dispersal of seeds and wingless arthropods, which is passive once these organisms have launched into the air. The novel findings from the model indicate that the epithet 'passive' often applied to the windborne migration of small winged insects is misleading and should be abandoned. The implications for the distances traversed by migrating aphids under various boundary-layer conditions are outlined.
Reynolds
Andy M
AM
Biomathematics Department, Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, UK. andy.reynolds@bbsrc.ac.uk
Reynolds
Don R
DR
D000392:Air Movements; D025041:Animal Migration; D000818:Animals; D001042:Aphids / Q000502:physiology*; D005426:Flight, Animal / Q000502:physiology*; D008962:Models, Theoretical; D011156:Population Density; D013269:Stochastic Processes
Biol Lett. 2007 Jun 22;3(3):237-40
17389214
Adv Virus Res. 2006;67:453-517
17027687
Bull Entomol Res. 2005 Apr;95(2):69-114
15877859
Bull Entomol Res. 2004 Apr;94(2):123-36
15153295
Nature. 2002 Jul 25;418(6896):409-13
12140556
Science. 1984 Mar 9;223(4640):1088-9
17830156