It must be ingested to poison, so it is nontoxic to birds, fish and beneficials. Pyrethrum is extracted from the flowers of chrysanthemum. It is a contact poison that affects the nervous system, paralyzing the insect. The insects produce an enzyme to detoxify the pyrethrum, so organo-phosphates, carbamates or synergists are sometimes added to slow the enzyme action. Piperonyl butoxide is a synergist found in many formulations.
Pyrethrum is extremely toxic to fish, toxic to bees and slightly toxic to birds.
Rotenone, a stomach and contact poison derived from the roots of two South American legumes, is sometimes added to pyrethrum, and is toxic to fish. Labeled for fruits and vegetables, it can also be used on ornamentals. Since capsaicin is acknowledged as a food, the EPA has exempted if from tolerance testing. It purportedly repels aphids, spider mites, thrips, leaf miners, whiteflies, leafhoppers and scale, as well as nibbling mammals. I haven t tried it, or know anyone who has, although I saw the product in a local hardware store.