The legal basis for implementing Cu/ex surveillance in individual countries is as follows: as part of a legal framework on disease surveillance (5/17 countries); based on specific legislation related to mosquito surveillance (Croatia and Portugal); and linked to the International Health Regulations (Portugal). Greece mentioned that the surveillance is embedded in the National Action Plan for WNV. In Portugal, surveillance supports national veterinary and human health legislation aimed at controlling zoonoses, especially those with potential for outbreaks or cross-border transmission. In the UK, the Cu/ex surveillance is linked to the UK National Security Risk Assessment and the National Adaptation Programme, which is related to the UK Climate Change Act.

Seven of the 17 countries implementing Cu/ex surveillance state that their Ministry of Health, at the national level, has the overall responsibility and oversight of vector surveillance and is legally bound to it. One country (Montenegro) mentions that it is the Ministry of Health at the sub-national level, and for one country (Serbia), it is the Ministry of Agriculture at the sub-national level that has overall responsibility and oversight of vector surveillance, while for Croatia, both these ministries have responsibility at the sub-national level. In Spain, the responsibility of entomological surveillance is linked to the 17 regions. In Greece, the Ministry of Health (National Public Health Organization) is responsible for mosquito surveillance at the national level, and the Ministry of the Interior supervises the regional and municipal authorities which are responsible for mosquito management at the local level. In Hungary, the Ministry of Interior is responsible for Cu/ex surveillance. In the UK, the UK Health Security Agency (UKHSA) coordinates mosquito surveillance with local partners.

In most countries, the Cu/ex surveillance plan is designed at the national level (11/17 countries) by the Public or Veterinary health agency (8/17 countries). Other entities responsible for the actual design of the surveillance plan are: a dedicated agency (the Netherlands), a working group within a ministry (Italy, Luxembourg, and Portugal), or a scientific or academic institution (7/17 countries). In Spain, this is the responsibility of the regions. In Greece, the surveillance plan is designed by a Public Health Agency (the National Public Health Organization) at the national level, and by the regional, municipal public health and mosquito management authorities at the sub-national (regional and municipal) level.

The evaluation and possible re-adjustments of the Cu/ex surveillance plan in most countries (14/17 countries) is done by the same organisation or agency that develops the surveillance plan. In the Netherlands, the surveillance plan is part of a plan for cost-effective WNV surveillance for the Netherlands 2025, which is being developed by a One Health consortium composed of various different institutes and agencies, chaired by the Dutch National Institute for Public Health and the Environment. There was a previous plan for WNV surveillance and control 2021–2023.

Five of the 17 countries evaluate and re-adjustment the surveillance plan annually, four countries (Italy, Luxembourg, Netherlands, Spain) do this every two to five years and four countries (Serbia, Slovakia, Slovenia, UK) mentioned that they never evaluate and re-adjust the surveillance plan. For four countries (Bulgaria, Croatia, Hungary, Malta), the respondents did not know this information.

The execution of vector surveillance is mostly done by public/veterinary health agencies (10/17 countries), or scientific institutions. One country (Netherlands) has a dedicated agency for the execution of Cu/ex surveillance. In three countries (Greece, Luxembourg, Spain), the surveillance is executed by private companies. In Greece, the national mosquito surveillance plan is executed by a Public Health Agency and scientific, academic, or research institutions, whereas the regional mosquito surveillance plans are executed by the regional and municipal public health/ mosquito management authorities through contracts with private companies. In Malta, the project-based surveillance was executed by the national infectious disease surveillance and control unit in collaboration with the 'Research Infrastructure Program on insect vectors of human and animal disease'. In Portugal, day-to-day mosquito surveillance activities, including field collection, species identification, and data reporting are executed by Local Public Health Units, under the coordination of regional public health entities and by the Reference Laboratory for Acarology and Entomology of the Instituto Nacional de Saúde (INSA). In Austria, the management of the traps is organised by the federal health directorates. This is organised differently depending on the federal state: in some, one person/institution (university, museum) is responsible for looking after all traps in the federal state, while in others individual locations are managed by employees of federal offices, employees of the Austrian Agency for Health and Food security (AGES), schools or private individuals. The samples are analysed by AGES. In the City of Vienna, the University of Veterinary Medicine is responsible for the implementation of the surveillance. In the UK, local landowners and local authorities assist with surveillance.