Key Words  
  Juvenile hormone, juvenoids, methoprene, fenoxycarb, pyriproxyfen
  The history of natural and synthetic bioanalogues of insect juvenile hormone (JH), juvenoids is more than 40 years old. The first JH-active lipid extracts prepared from the cecropia moths in 1956. The first JH-active was an isoprenoid farnesol isolated in 1961, then “pseudojuvenilizing” or JH-mimetic effects of lipids were described; after 1965, JH-active isoprenoids were isolated from natural sources. A sesquiterpenoid ester, juvabione, was isolated from paper products, and a isoprenoid compound with JH activity was isolated from the lipid extracts of cecropia. It was an acyclic sesquiterpenoid ester known as the true JH of insects, the JH-I. Major achievements of 1965-1975 this epoch were registrations and practical applications of the isoprenoid juvenoids, hydroprene, methoprene and epofenonane. They were used against mosquitoes, synanthropic flies, pharaoh’s ants and cockroaches. Since 1980, commercial interests in juvenoids moved from isoprenoids to the polycyclic juvenoids, which were characterized by the presence of 4-phenoxyphenyl structure. The first juvenoid of the 4-phenoxyphenoxy series registered for practical use was fenoxycarb. This juvenoid has been successfully used against various insect pests. Another juvenoid of this series, pyriproxyfen which like fenoxycarb exhibits very high JH activity. In certain species it is more effective than fenoxycarb, but in other species the proportions may be reversed. Data concerning the action of methoprene, fenoxycarb and pyriproxyfen are provided. There may be thousands of synthetic juvenoids which mimic the action of insect hormones. The authentic JH of insects interacts with the genome of insect cells and produces the qualitative, “all-or-nothing” effect. This enables the hormone to act in concentrations close to 10-10 M, first recorded in peptidic juvenoids in 1973. The 10-10 M limits of JH activity were again found in the modern juvenoids containing the bicyclic, phenoxy-phenyl groups; fenoxycarb, pyriproxyfen and other structurally related juvenoids. At 10-10 M concentrations the endogenous JH and the most potent juvenoids are protected from and uninfluenced by esterase and other hydrolytic enzymes. The isoprenoid compounds, JH-I or JHIII, are mostly 10000-times less active than synthetic juvenoids. JH-I, JH-II and JH-III are not the true JH of insects, but misinterpretations of physiologically inert prenol metabolites. The true JH of insects is probably a small peptide.