The western flower thrips Frankliniella occidentalis (Thysanoptera: Thripidae) is a major insect pest on a wide range of crops throughout the world. There are several unexplained aspects of the mating behaviour, particularly in relation to male-male competition and mate choice. The objectives of the study were to test whether males can detect the mating status of females and whether males avoid mating with previously mated females. Experiments involved either 'experienced' adults taken from a laboratory culture, which had been exposed to high densities of thrips, or virgin adults reared individually. Experienced males mated readily with virgin females, but avoided mating with experienced females. Virgin males showed much less discrimination between females. Avoidance of mating with experienced females is likely to be widespread because it occurred in populations from both the United Kingdom and Kenya. Experienced males also mated with dead virgin females, but avoided mating with dead experienced females, which ruled out the possibility that behavioural differences between the females were responsible. To test whether males could detect whether or not females had mated, virgin females of the same age from the same cohort were either mated once or not mated. Experienced males mated with the dead females that were virgin and avoided mating with the dead females that differed only in that they had mated once shortly before. This showed that males recognise whether or not a female has mated and avoid mating with previously mated females. This avoidance by males suggests that mated females are not usually subjected to high levels of male harassment. The most likely explanation of the avoidance is that males produce an antiaphrodisiac pheromone that is applied to females during mating.