The new species Parapygmephorus (Sicilipes) costaricanus (Pygmephoridae: Neopygmephorinae) is described from adult females, males, and larvae, and distinguished from Р. (S.) halictinis. Adult females are phoretic оп adult Agapostemon nasutus and detach from female bees when the bees construct or provision nest cells. The mites oviposit vhen the mature Ьее larvae defecate and the mite larvae feed uроп some compol1ent or contaminant of the Ьее feces. Adult male mites сапу pharate females with their enlarged hind legs and the mites copulate before their hosts moult into adults. Adult female mifes attach to tl1e emerging adult bees. These mites are evidently commensals of bees and their life cycles are closely synchronized with those of their hosts. The biology of these mite species associated with bees previously has not Ьееп described. This species occurs not опlу in Costa Rica but also in Mexico, according to Е. А. CROSS.