Google-search led me to Ellen Pifer's 2003 "Vladimir Nabokov: Lolita, a Casebook" where she indicates Nabokov's quote from Shelley's Ode to a Skylark. in an intriguing context.

"Betraying him at every turn, the narrator's rationalizations are as intriguing in their self-exposure as those of his literary precursor Victor Frankenstein. Humbert's striking kinship with the protagonist of Mary Shelley's novel appears to have gone unnoticed - perhaps because the characters appear to have little in common."*(19)

*(19) Although Humbert's narrative never directly refers to Frankenstein, Nabokov, [ ] undoubtedly read Shelley's popular classic in his youth.[ ]Nabokov's prodigious knowlege of the English Romantics- Byron, Wordsworth, and Percy Bysshe Shelley - as well as their European precursors, contemporaries, and epigones is both obvious and well documented. Nabokov, in his commentary on the translation of Eugene Onegin refers to Shelley's "widow" when glossing a line (chap. 3 stanza 9,18) of Pushkin's novel in verse: "According to his widow, "Nabokov comments, "one summer evening [the poet] heard the skylark and saw the 'glow-worm golden in a dell of dew' mentioned in his famous ode" (2.344).