I would not go out of my way to destroy a mosquito but if it insists on attacking me, disturbing my daily activity or nightly sleep, then my killing of it in self-defense is ethically justified, if harmless precautions like screening windows and netcurtaining the bed have been taken but fail to keep it away.

-- Notebooks Category 6: Emotions and Ethics > Chapter 7: Miscellaneous Ethical Issues > # 10