A campaign in New South Wales against flying swarms of the Australian Plague Locust, Chortoicetes terminifera (Wlk.), using Tiger Moth light aircraft, is described. Large rolling swarms of this locust, travelling across the open plains of western New South Wales, are directed in their general south-easterly move ment by natural barriers in such a way that regular migration routes are followed and predictions of swarm movements can be made. Of particular importance are the timber fringes of creeks and rivers which tend to baulk swarms temporarily and it was in such situations that locust swarms proved most susceptible to treatment by a manoeuvrable aircraft.

A technique of drift spraying was developed wherein aircraft were able to operate without ground direction against travelling swarms by spraying at right- angles to the wind direction and by using the main body of the flying locusts for demarcation. Large numbers of short spraying runs were made in rapid succes sion over the most dense portions of the swarm being treated until control was achieved. It was found that the spacing of the runs was not particularly important as long as each was applied to the densest portions of the swarm. The light and relatively slow-moving Tiger Moths proved highly suitable for this work and they were also useful for scouting and keeping track of swarms. Observations made after spraying indicated that the coherent flying swarms treated in the open plains were almost completely eliminated. If, however, swarms were able to reach closely settled or heavily timbered areas they tended to split and disperse and were difficult to treat. The insecticide used was an emulsifiable concentrate containing 7 per cent. γ BHC, which was diluted with diesel oil, and one gallon of liquid containing 5·6 oz. of γ BHC was designed to cover one acre. However, as the campaign progressed, effective use of the spray was probably obtained at less than one gallon per acre, and a total area of 30–37 square miles of dense swarms was treated at a cost of approximately £13,700. There is scope for an improvement in the efficiency of the spraying technique as well as a reduction in some of the major costs in any future campaign.

It was considered that the campaign carried out in the Ivanhoe—Hillston district completely controlled all swarms in the area and protected from invasion valuable farming lands to the south-east. Further spraying operations, in the Jerilderie district, 150 miles away, were less successful, although many mor locusts were killed. The spraying party arrived in the district too late to plah a strategic campaign and some swarms escaped treatment.

It is concluded that the method of aerial drift spraying is capable of wider application in Australia, particularly in areas where problems of distance, popula tion and lack of facilities militate against successful control by ground machinery.