Predatory mites double the economic injury level of in strawberry.

The western flower thrips (Pergande) (Thysanoptera: Thripidae) causes bronzing to strawberry fruit. Management of insecticide-resistant strains relies on the integration of predators with carefully timed use of the few insecticides available. Effective management requires better understanding of economic injury levels (EILs) and the factors that affect them. The densities of and the predatory mite (Oudemans) (Acari: Phytoseiidae) were manipulated in field experiments. All stages of flower and fruit were susceptible to thrips damage, but larvae caused nearly twice as much damage as adults per individual. The EIL was about four adult thrips per flower in the absence of predators, but increased to over eight at densities of typical of good establishment in crops. The EIL could be increased by about 0.7 adult thrips per flower for every per flower. The results were supported by measurements of EILs in commercial crops.