re: Mosquitoes
It takes a remarkably small amount of still water for mosquitoes to breed. A bit of leftover rainwater in the bottom of an old tire, or the hollow of an old stump, is all that's needed.
My grandfather kept mosquitoes out of the cattle water trough with a drop or two of oil, which spread over the surface and clogged their little larval breathing tubes. Too small an amount to bother the cows.
My pond out back is stocked with mosquito fish to keep the bugs out. Our local control people will cheerfully bring you a few dozen fish for free on request.