Abstract: A series of four trials evaluated the potential of Steinernema feltiae and S.carpocapsae to control Tuta absoluta larvae in tomato leaves. In an initial ‘proof of concept’,high rates of 10 million nematodes/litre were found to be as effective as spinosad. The secondtrial demonstrated that 80% mortality could be achieved with 1 million S. feltiae/litre at a costcomparable to the standard chemical insecticide. The third and fourth trials evaluated the lowerapplication rate on a large scale in a 1.17ha tomato crop using the nursery’s own robotic sprayequipment. This provided 40-50% mortality. Steinernema feltiae could make an importantcontribution to the overall IPM programme by slowing down the population growth of T.absoluta while the primary biological control agents (Nesidiocoris tenuis or Macrolophus spp.)become established. This could be particularly important in organic tomato crops where there arevery few effective alternatives.