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 d amaging pest of protected cucumbers in the UK and reliable control measures are required that are compatible with other components in the IPM programm e. Although the predatory mite, Amblyseius cucumeris Oudemans (Acarina: Phy toseiidae), has been used for thrips control for many years, results agains t F. occidentalis in cucumbers during the early 1990s were frequently unacc eptable. Three experiments in 1994/95 evaluated a prophylactic approach to the control of F. occidentalis. This involved placing one A. cucumeris cult ure sachet on each plant immediately after planting. F. occidentalis was re leased 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. occi dentalis populations was almost entirely suppressed when the culture sachet s were placed immediately after planting. Thrips damage was reduced compare d to untreated controls when introduction of culture sachets was delayed by 2-4 weeks but this increased the risk of control failure.