Insects are killed by being deprived of oxygen to the tissue cells. It takes about 2-3 days to kill insects. It is toxic to fish. Pyrethrum can kill insects rapidly at very low concentrations. Generally flying insects are killed quickly.
Pyrethrum is also toxic to fish.
Rotenone works mainly on beetles, aphids, leaf eating caterpillers, plant bugs, leaf hoppers, spider mites, whiteflies, thrips and blister beetles. Pyrethrum is effective on aphids, codling moths, leafhoppers, spider mites, stink bugs, thrips, whiteflies, gnats, houseflies, pantry pests and mosquitoes. It can be used on vegetables, fruits, trees, ornamentals, houseplants and in greenhouses up till one day before harvest. You can apply with a hose end sprayer, compression sprayer, power sprayer or a squirt bottle.