Malaria-carrying mosquitoes are thought to all be strictly nocturnal. Recently, this dogma has started to be questioned, mainly because the rates of malaria did not significantly diminish in areas where bed nets have been implemented.
However, based on some basic observations of the past two months in Tanzania, the rates of malaria have also not significantly diminished because people don't use the nets. I saw plenty of successful fisherman bringing in great catches with the blue PSI nets. Just because the bednets have been handed out, doesn't mean people use them properly. Especially if they don't sleep in beds.
Embarrassingly belated hat tip: My dad