See if you can get a clear picture of the little white dots, and post it?
Unless your fly spray was a systemic insecticide, it's not going to have any residual effect. Most insecticides are contact effect. i.e. you have to hit the insects to kill them. That's why it's just as good, and less toxic to everybody but the bugs to use the soapy water spray.
More likely the white spots are burn marks on the leaves from the stuff. It won't hurt the plants much as long as the rest of the leaves are nice and green.
