Suppressing establishment of Frankliniella occidentalis Pergande (Thysanoptera: Thripidae) in cucumber crops by prophylactic release of Amblyseius cucumeris Oudemans (Acarina: Phytoseiidae)

Frankliniella occidentalis Pergande (Thysanoptera: Thripidae) is the most damaging pest of protected cucumbers in the UK and reliable control measures are required that are compatible with other components in the IPM programme. Although the predatory mite, Amblyseius cucumeris Oudemans (Acarina: Phytoseiidae), has been used for thrips control for many years, results against F. occidentalis in cucumbers during the early 1990s were frequently unacceptable. Three experiments in 1994/95 evaluated a prophylactic approach to the control of F. occidentalis. This involved placing one A. cucumeris culture sachet on each plant immediately after planting. F. occidentalis was released in all crops to ensure that the biocontrol measure received a severe test. Treatment was compared to untreated controls and the delayed release of culture sachets. The cultures remained active and produced populations of A. cucumeris on leaves for at least nine weeks. Establishment of F. occidentalis populations was almost entirely suppressed when the culture sachets were placed immediately after planting. Thrips damage was reduced compared to untreated controls when introduction of culture sachets was delayed by 2-4 weeks but this increased the risk of control failure.