A. As with all actions, it is your volition that is the important factor. To kill because one enjoys killing cannot be wholesome, and will have its consequences. If it is your health that concerns you, then take one of the numerous precautions that are available, that way you won’t have to kill them. Or you could reflect on metta and take the attitude that the mosquito has as much right to be here as you and let them have a spot or two of blood. It’s very unlikely that you will come to any harm and it will surely give them a few moments of pleasure and fulfilment in a precarious life that is short and full of anxiety.