You don't owe them any further explanation, but I would give it to them in hopes they leave you alone when they realize you caught them with their hand in the cookie jar. 

I do annual spraying. 

A lot of people think they're going to love it here until they get here and realize visiting a resort (with 24/7 A/C and weekly pesticide spraying) isn't quite the same as really living here. 

So, they can actually be your eyes on the condition of the property.In your shoes, if you think they are causing the problem, I'd suggest you have a pest control that must enter the unit as well as spray outside - once a month.  

Spray on pop corn is easily scraped and the drywall finished.

The Tom' spray never comes out. $10,000 cat.  

We now do quarterly inspections of our properties to make sure tenants are not painting, changing light fixtures, installing backsplashes, staining kitchen cabinets, spray painting the patio, etc.

Spray painting, broken windows etc.Thanks for any, possibly calming, advice and reassurance 

I talked to a professional painter friend. he had me spray a clorox /water  mix on all the walls about knee high down. and spray door frames heavy. 

If that happens is it up to me to go over there with my can of wasp spray and deal with it, or do you all let the tenants handle this?