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...10 will be left alive and cannot be killed by that particular spray.

And if the bugs no longer get sprayed, what will the future population be like?

Do the non-resistant bugs outproduce the others? or the other way around? Or does the ratio stay the same?

"Do the non-resistant bugs outproduce the others? or the other way around? Or does the ratio stay the same?"

Considering that the 'others' are dead, I'd say yes for at least one generation. Now, there may very well be mutations or other genetic changes in the next generation that cause some of the bugs to not have their parents' immunity to that particular spray. In that case, their ability to reproduce, in the absense of the spray that would kill them, could be greater or less than that of those who have carried over that immunity. That would depend on exactly how their genetic traits serve them in their current environment. Any genetic change can have consequences ranging from nothing to death.

The reproductive potential of one organism in a species as compared to another merely depends on how fit they are for their environment. The changes that allow for the immunity to the spray may have other consequences that decrease the reproductive potential for those who have the immunity, or it may increase that potential. That's the fun part of genetics - trying to figure out how specific changes fit into the grand scheme of things in terms of the organism, its genetic traits, and its fitness for its environment.

This is still incredibly simplistic, but accurate in a general sense. It makes sense when you think it through.

And if the bugs no longer get sprayed, what will the future population be like? Do the non-resistant bugs outproduce the others? or the other way around? Or does the ratio stay the same?

No way to tell. When the spraying stops that evolutionary pressure is eliminated. The proportion of bugs that have spray resistant genes will be at a higher level though.

This is why it is so important to kill off all members of a rapidly reproducing species (insects, bacteria) population before they can adapt and become resistant. This is why doctors insist that antibiotics shouldn't be taken unless the patient will take the whole dose.