Concentration of flying insects by the wind

Abstract

The role of horizontal wind convergence in concentrating flying insects is examined. Because of the inverse relation between intensity and persistence of convergence zones, a tenfold increase in volume density is unlikely to be exceeded in a single atmospheric disturbance, and then only if the insects are not taken through the convergence zone. Radar has shown that the commonest disturbances associated with insect concentrations are windshift lines: modifications of the broad-scale wind flow due to buoyancy and blocking effects. Even in the absence of concentration, a tenfold increase in area density can be brought about by vertical circulations at windshift lines. Insect concentrations are likely to be most frequent and persistent at night, and over and near mountains, where searches are most difficult.