During 2007 and 2008, natural mite mortality was recorded in honey bee colonies. These colonies were then treated with various acaricides against Varroa destructor and acaricide efficacies were evaluated. In 2007, experimental colonies were treated with flumethrin and/or oxalic acid and in 2008 the same colonies were treated with flumethrin, oxalic acid or amitraz. The efficacy of flumethrin in 2007 averaged 73.62% compared to 70.12% for three oxalic acid treatments. In 2008, a reduction of 12.52% in mite numbers was found 4 weeks after flumethrin application, while 4 oxalic acid applications produced significantly higher (P < 0.05) mite mortality, an average of 24.13%. Four consecutive amitraz fumigations produced a 93.82% reduction on average in final mite numbers and thus ensure normal colony development and overwintering. The study is important in order to demonstrate that synthetic acaricides should be constantly re-evaluated and the use of flumethrin at low efficacies need to be superseded by appropriate organic treatments to increase the efficacy of mite control in highly-infested colonies during the period of brood rearing.