In the spring 2006, a flood emergency occurred in the Olomouc region after a rapid snow thaw, with the formation of multiple periodic pools and overflows persisting for long periods. In the floodplain forests, as expected, mass occurrence of adult mosquitoes was observed, infesting the nearby villages. The mosquito emergency continued until August and mosquitoes of both the spring species, in particular, Ochlerotatus cantans, and summer species were implicated in it. To control this emergency, aerial application of VectoBac G larvicide granules based on Bacillus thuringiensis var. israelensis (BTI) at a dose of 6.4 kg/ha was used for the first time in the Olomouc region. Its efficacy was close to 100 % for the treated water areas. The effect was clearly evident in the communities situated in the vicinity of the treated breeding grounds. Nevertheless, not all breeding grounds and blind stream meanders could be treated aerially. As a result, mosquitoes from the untreated breeding grounds caused an emergency in the nearby communities where insecticide aerosols had to be applied on a large scale, even repeatedly in some cases. The treatment of the mosquito breeding grounds with BTI based larvicide granules proved to be an effective and fully selective approach to controlling mosquitoes. Although the technology is exacting and requires professional and organizational skills, it is expected that, in the Czech Republic, this environmentally friendly approach to mosquito control will replace the large scale use of non-selective chemical aerosol insecticides. The public health protection, administrative and legislative authorities should be active in promoting the use of specific BTI based larvicides for the treatment of mosquito breeding grounds, even if located in protected areas, whenever it is needed for mosquito control in emergencies.

        Key words: flood – mosquito emergency – Bacillus thuringiensis var. israelensis – mosquito larvae control – larvicide.