Due to their action as stomach poisons and rapid degradation they can be more selective against pests than against beneficial species. Most BI's are nontoxic to plants. Nicotine sulfate may be harmful to some ornamentals. Not all BI's are less toxic than all synthetics and should be handled accordingly. BI's tend to cost more than synthetic insecticides, and are not as readily available.
Potency often varies from among batches.
Tolerances for residues of some materials have not been established. Some are not registered for use in certain states. The source of Pyrethrum and Pyrethrins is powdered, dried flower heads of the pyrethrum daisy that is grown mostly in Kenya. The mode of action is disruption of nerve function. The pyrethrums cause rapid knock-down and paralysis.