  We prove that a variety of Novikov algebras has a distributive lattice of
subvarieties if and only if the lattice of its subvarieties defined by
identities of degree three is distributive, thus answering, in the case of
Novikov algebras, a question of Bokut from about fifty years ago. As a
byproduct, we classify all Koszul operads with one binary generator of which
the Novikov operad is a quotient.
