Frankliniella occidentalis (pergande) is a serious pest of protected crops within the UK because it damages crops and is a vector of tospoviruses. It is resistant to a wide range of insecticides and exhibits thigmokinetic behaviour, making contact between pest and treatment difficult. Applying control procedures to correspond with the diel behaviour patterns of F. occidentalis could enhance control ofthrips. Studies of glasshouse crops showed that the abundance of adults on leaves and flowers increased in ~he afternoon compared to the morning. This could not be accounted for by movements within or between plants, but could be from sites off the plant. This hypothesis deserves further investigation. Infrared videography in the glasshouse generally showed little difference In abundance on plant parts between scotophase and photoppase. In addition, observations made at the time suggested that there was little difference in locomotory activity between the light phases. Contrastingly, laboratory locomotory activity patterns showed an increase in the early morning and late afternoon. A light burst during the scotophase, devised in the lliboratory to enhance locomotory activity, had little effect on thrips in a cucumber glasshouse. These two findings cast doubt on the applicability of laboratory studies to the glasshouse. Flight could be predicted well using ambient light and temperature and showed a clear diel pattern. There was a diel pattern of larval dropping to the ground to pupate, with the majority of larvae falling between late afternoon and midnight. Further sampling within a ,?ucumber glasshouse showed that on any particular day most larvae dropped within a two-hour window. Flight activity, and larvae falling from the crop showed clear' diel patterns. Locomotory activity on the crop djd not show a clear diel pattern. Interpretation and use of these findings would depend upon the type of control procedure applied to a crop.