Regarding the following passage:
"Sladko! (Sweet!)" Pushkin used to exclaim in relation to a different species in Yukon.
Is it possible that Nabokov's particular usage of "sladko" (sweet) here is a reference to the Russian wedding custom of wedding-goers loudly exclaiming "gor'ko! (bitter!), to encourage the couple to kiss, at which point the taste becomes "sladko" (sweet)? Especially given that the entire chapter is about lips, kissing, and the insatiable appetites of both Van and the mosquitoes for Ada's skin.
Apologies if this has been pointed out before; I searched online for annotations but did not see this particular interpretation.