Rotenone from derris root paralyzes the insect cardiovascular and respiratory system. D-Limonene from citrus pulp may produce idiosyncratic toxicity in cats and at the present time is not recommended. Chlorinated hydrocarbons are not recommended any more. They kill by CNS toxicity. They should not be used in cats.
Chlorinated hydrocarbons remain in the environment and are therefore of concern.
Organophosphates are not recommended any more. They work by irreversible inhibition of cholinesterase. They are adulticides, however fleas may become resistant by increasing their ability to detoxify. Cats and young animals are very sensitive to the toxicity of these products. Clinical signs include weakness, ataxia and deficits of conscious proprioception that may progress to paralysis.