Investigations into the biology and behaviour of Thrips tabaci L.

Abstract

The onion thrips, Thrips tabaci (Thysanoptera, Thripidae) is a polyphagous pest of Allium crops in the UK and considerable effort and expenditure is employed in its control. Despite this, overall understanding of the biology and behaviour of T. tabaci is poor and this project addresses some of these deficiencies in knowledge. The relationship between T. tabaci development and temperature was investigated using linear and non-linear descriptors. The most accurate descriptor was a non-linear logistic curve. A forecasting system was developed to predict population trends in the field using field temperature data to estimate the progression of development over time. It was not possible to predict field population trends accurately and possible reasons for this are discussed. The effect of temperature and of leaf quality on behaviour was examined. A range of different behaviours were identified, classified and shown to have a direct relationship with both temperature and leaf quality. The potential for such information to help to explain and predict patterns of behaviour seen in the field is discussed. The diel periodicity of the intra-plant distribution of T. tabaci was examined and a clear pattern identified. A high proportion of adults were located on exposed portions of host plants in the early afternoon. An experiment was conducted, focusing on this potential window of vulnerability, using a novel control technique involving irrigation. No significant control of thrips was achieved, but further investigations into the potential of such strategies are recommended. Field populations of T. tabaci were monitored between 2004 and 2008. Throughout this period thrips were most numerous in late summer and overwintered as adults. The monitoring data were examined in light of what has been learnt about T. tabaci biology and behaviour in this study. Recommendations are made about future work on forecasting and control