The natural pyrethrins from the daisy-like flower, Tanacetum or Chrysanthemum cineraruifolium, are
nonpersistent insecticides of low toxicity to mammals. Synthetic analogs or pyrethroids, evolved from the
untural compounds by successive isosteric modifications, are more potent and stable and are the newest
inportant class of crop protection chemicals. They retain many of the favorable properties of the pyreUwns.