The present invention in general relates to the field of biological crop protection by use of phytoseiid predatory mites. More particularly the present invention relates to a system for releasing a phytoseiid predatory mite in a crop and novel uses of host mites in such phytoseiid predatory mite releasing system. The phytoseiid predatory mite releasing system according to the invention and the uses according to the invention are characterised by the selection a host mite species having an intrinsic growth rate (rm) of <；0.28.
