After the successful spraying and control of tsetse fly in the northern portion of the Okavango Delta in 2001 the decision was made to continue with the aerial spraying using sequential aerosol doses of the insecticide deltamethrin in the remaining southernmost portion of the Delta in 2002. Meteorological and spray deposition data showed considerable variation between sites. Wool strands used to investigate the extent of residual effects of an application of 0.3g/ha of deltamethrin during cycle 2, revealed that such effects were likely to have lasted for four or five days after the spray event.