Sumithrin is a type I pyrethroid insecticide. Pyrethroids are synthetic versions of a natural insecticide produced by chrysanthemum flowers. Although pyrethroids are among the least toxic insecticides, they are nerve poisons. They act upon the sodium ion channels in nerve cell membranes.
The pesticide containing sumithrin being used in New York City and its suburbs is called Anvil. It is 10% sumithrin, 10% piperonyl butoxide and 80% inert ingredients. Piperonyl butoxide makes the pesticide more effective by preventing insects from detoxifying sumithrin.
Manufacturers are not required to disclose the inert ingredients, although they may be toxic also.