We had those growing up in suburban Chicago too -- in my case in the 70s. The trucks would only appear at dusk. We dumb kids thought the fog was a hoot so we would jump on our bikes and chase behind the truck hooting at the novelty, breathing in who knows what chemicals. I can still remember the smell.

It was probably malathion, which is an organophosphate pesticide that is considered low toxicity, although it may be a carcinogen.

> breathing in who knows what chemicals

Probably DDT. Not thwebest of ideas!

In the 1970s? No, almost all use of DDT in the US ended in 1972.

I seem to recall this in the Midwest as recently as the 90s

My dad told me similar stories from midcentury New York.

In FL, we still have the mosquito truck end up coming by at least every other week.

I don't think we do it for malaria these days, just to reduce mosquito stings? Thinking about like mosquito sprays in Chicago...

AFAIK it's more about West Nile and EEE, maybe Zika and even others.

Though, incidentally, if you reduce/eliminate mosquitos carrying West Nile, Zika, etc ... you also reduce/eliminate the ones carrying Malaria :)