Margosan-O works as an insect growth regulator. The treated insect usually can't molt to its next lifestage and dies. It also may deter egg laying. Do not expect a quick kill. The active ingredient, pyrethrin, is extracted from a chrysanthemum plant, grown primarily in Kenya, Rwanda, Tanzania and Ecuador.
Most insects are highly susceptible to pyrethrin at very low concentrations.
The compound acts rapidly on insects, causing immediate knock down. Flying insects drop almost immediately after exposure. PBO, however, is not certified to be used on organic crops. Growers, who want to meet organic certification standards, should consult with the Colorado Department of Agriculture before using pyrethrin products. Pyrethrum is non-toxic to most mammals, making it among the safest insecticides in use.