After playing this game occasionally for over a year, I finally managed to win today. At first, I thought the difficultylevel was way too high, but I must say, it is pretty satisfying to beat all the levels at such an insane pace.
Couple of hints: boost up your repairmen (I used 8) asap by leaving a couple of bugs gnawing away at the walls and repairing those walls. As soon as I had 8 repairmen, that is what I did and then proceeded to watch the movie Gomorra. Any other movie will do as well.
At the final 10 levels, I sold one mortar and got me another machine gun turret (3 in total). That helped me survive the airbug levels.