Which insecticide is least hazardous to human health?

Pyrethrum is a natural plant product which contains 6 active esters known as pyrethrins which work in combination to kill insects. Pyrethrum affects the central nervous systems of insects and disrupts normal function. In the lowest concentration, this affects insect behaviour. At slightly greater concentration, soon knock them down and kill them. As it is a natural insecticide it has the least hazardous effect on human health in comparison to DDT and rotenone.