Relative abundance and temporal distribution of adult Frankliniella occidentalis (Pergande) and Frankliniella schultzei (Trybom) on French bean, lettuce, tomato and zucchini crops in relation to crop age

Field studies assessed the differences in temporal distribution and abundance of Frankliniella occidentalis and F. schultzei on French bean, tomato, lettuce and zucchini from one week after planting to senescence or harvest. Ten samples each of three plant parts leaf and stem, flower and growing tip samples were collected at weekly intervals, in eleven field plantings in the Lockyer Valley (south-east Queensland, Australia) over a three-year period from December 2011 to June 2014. There were significantly more F. schultzei than F. occidentalis in lettuce and tomato, and significantly more F. occidentalis than F. schultzei in French beans. Zucchini supported the highest abundance of both species, with no significant difference in mean abundance. Both species displayed similar preferences for different plant parts, with significantly more in flowers compared to leaf and stem and growing tip samples. There were significantly more thrips in female zucchini flowers compared to male flowers. Thrips were present in small numbers one week after planting in all crops, with peak abundance at flowering. F. occidentalis were temporally segregated by crop age (weeks since planting), with significantly higher levels present in zucchini compared to French bean, lettuce and tomato between weeks three and six, followed by significantly higher levels in French bean between weeks eight and ten. F. schultzei were temporally separated by crop age between zucchini and lettuce, with significantly higher levels present in zucchini between weeks four and six, and in lettuce between weeks eight and ten. Implications for crop monitoring are that sampling should be concentrated at pre-flowering for F. occidentalis in French bean and zucchini and for F. schultzei in tomato and zucchini. For lettuce, the seedling stage is most vulnerable to infestation by both species. Growers should be aware of the potential for both Frankliniella species to disperse from senescing zucchini flowers from week seven and aim to implement control strategies around this period.