I'd also seen them at Walmart.
Audrey's comment on immunity jogged my memory - when I spent the better part of last summer in the Oregon Cascades, the mosquitoes were fierce, so bad during early July you'd inhale a few, particularly in the morning when they first came out around 7AM. DEET helped, but only so much. Funny thing is - the bites didn't itch. Or at least for the first 10 days, and then - zowie, did they ever! Couldn't figure it out until someone (happened to be an MD) mentioned that my body needed a week or two to build up antibodies as it must not have ever "seen" this particular variety before. Once the antibodies came up to speed they itched like every other mosquito bite I've even had.