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The soil dwelling predators from family Laelapidae are subjected to the influence of all the cultural practices, connected with tilling, use of organic fertilizers, amendments, etc. In 2005-2006 tests were carried out at laboratory conditions at Agricultural university – Plovdiv with two mite species Gaeolaelaps aculeifer (Canestrini 1884) (=Hypoaspis aculeifer). Four different rates of augmentation were used: 5, 10, 20 and 50 mobile stages per plant. The Western flower thrips Frankliniella occidentalis (Pergande 1895) was used as prey. The influence of two organic fertilizers (AgroBiosol and Kompovet B4) was tested on the mite populations. The results showed that adding organic fertilizers to the soil substrate influenced the density and structure of the population and the regulating abilities of the predatory mites. in the variant with organic fertilizer added the population density of the mites increased 2 to 5 fold, compared to the control. In this variant the structure of the population was predominantly of mobile immature stages, the percentage of which always exceeded that of the adults and varied from 51.39 to 82.35% in the variants with different organic fertilizers. By favoring the deveioprnent of the predatory mites the organic fertilizers lead to enhancement of the regulating abilities of the mites for the thrips – the level of damage caused by the thrips and its population density decreased by 45%.