THE ACQUISITION OF AERIAL U.L.V. SPRAYS BY AUSTRALIAN PLAGUE LOCUST NYMPHS, CHORTOICETES TERMINIFERA (WALKER)

The direct and indirect modes of insecticide acquisition by Chortoicetes terminifera nymphs in the field were investigated by measuring insecticide content in nymphs collected at intervals from grassland which had been sprayed from the air with fenitrothion 1.28 kg L ‐1 , In sparsely vegetated pasture, acquisition was mainly by direct droplet impaction. Residual (indirect) acquisition occurred in addition to direct impaction and became dominant when the nymphs were sprayed in relatively dense pasture. Residual insecticide was accumulated during the first hour or so after treatment, at a rate which was approximately proportional to the residue level on the grass and the amount of grass available. The nymphs accumulated residual insecticide presumably from contact and feeding on the contaminated grass; collection from deposit on the soil surface was negligible.