manna a sweet substance appearing at certain seasons on a wide range of plants, from trees to grasses. Manna is associated with infestation by scale insects, but it is often unclear whether the manna is exuded by the plant as the result of insect wounds or is, like honeydew, a secretion of the insects themselves. Because of the multiplicity of sources, the identity of a given manna is often debatable. Donkin (1980), in a book-length monograph on the subject, has made the greatest single contribution to such debates.
