According to the 2014 CR Calculator, if we give the Male a DPR of 15–32 he'll be Challenge 2, with DPR 6–14 he'll be Challenge 1 and with DPR 4–5 he'll be Challenge 1/2.
The AD&D Male Giant Mosquito was worth 420 XP compared to 975 or 1,400 for the Females, so I think CR 1 is most appropriate...