There are less in dryer weather, but then where there are plants that need watering by gardeners using 'dirty water', fresh water, or there is stagnant water lying around, there could be more mosquitos.
If worried about the Zika virus, please check your government information websites for up-to-date information.
You can buy mosquito repellent in a few shops but as always, it is better to bring your own as it can be more expensive (as like sun lotions and sprays) and not always available!
Others may want to bring some plug-in mosquito tablets/liquids for the apartment/hotel room. You can also buy a pack of mosquito coils from local shops,
once lit they burn slowly, one will last for about 6hrs, but they do give off a strong smell if used in small enclosed areas with no ventillation........
have these coils passed any European standard test? Who knows!
British Nationals can find further contact information about dengue fever or malaria within: British-Gov-Health-Information.