I am not a part of the circuit under test).
You can see around where the bridge rectifier diodes are the short the insect created, it goes from primary to secondary??
So ...It is no surprise that the logic is attached to the mains. This is normal in dishwashers, brushless motor washing machines, but not generally microwave ovens (well, certainly not the older ones).You really did have a "bug". Not at all uncommon.One such (in the dishwasher) attempted to burn down my kitchen some years ago when it bridged a solenoid. Even before that, I adopted the practice of completely covering either all possible entry points (including surrounding the control knobs) or covering the control board (or both) of kitchen appliances - microwave, dishwasher, cooktop - with flyscreen mesh, secured with hot melt glue (away from the hot parts, of course). A necessary alternative (but could equally be, addition) to frequent applications of insecticide everywhere.