Few things are more annoying than mosquitos flying around your head during hot summer nights while you try to sleep with the windows open.
If your bedroom has steel-framed windows, try this solution: buy flyscreen gauze (the nylon type) from your local hardware store for about R19/m2.
Next, visit your nearest appliance repair centre, ask them for old fridge or freezer door seals, and remove the long, flexible magnets inside.
Cut the flyscreen gauze about 15-20 cm bigger than your window frame and attach it with the flexible magnets. I have been doing this for the past two years and enjoy a peaceful sleep.