The aggregation pheromone of the western flower thrips, Frankliniella occidentalis (Thysanoptera: Thripidae), has previously been identified as the monoterpenoid ester neryl (S)-2-methylbutanoate. It attracts both male and female adults to traps in commercial glasshouses. In this paper, we investigate the rates of production of this compound at two male densities and in the presence or absence of an adult female. Solid-phase microextraction (SPME) was used to entrain live-male headspace odour and this was compared with external standards to obtain an estimate of pheromone production, which was about 100-300 pg male^-1 h^-1. Significantly more pheromone was apparently produced per male at the higher density, but no firm conclusions could be drawn because the rates were close to the limits of resolution. The rate of production was not affected by the presence of a female thrips. Another male-headspace component, (R)-lavandulyl acetate, was only detectable at the higher male density.