JH esterase plays a crucial role in the decrease of JH activity in lepidopteran insects, by hydrolyzing the methyl ester of JH. It is also involved in the transport of JH. H2O + juvenile hormone I = H(+) + juvenile hormone I carboxylate + methanol H2O + juvenile hormone III = H(+) + juvenile hormone III carboxylate + methanol Fat body, the site of their biosynthesis, and the hemolymph where it is secreted. Belongs to the type-B carboxylesterase/lipase family.