Thanks to Welch’s love for the music, he and the company are about to unveil their first staging of the mythology-based work, which premiered in a luxe Paris Opera Ballet production in 1876. Sylvia, the tale of a shepherd’s love for a forest nymph, is the first of four full-length story ballets that Houston Ballet has in store from now through June. The coming ones include the other great beneficiary of Delibes’ gifts, Coppélia.