Frass is not a pesticide....rather an excellent source of chitin. Chitin stimulates an immune response in plant, plant creates chitinase, an enzyme, which turns the chitin into chitosan, which is growth enhancer & boosts plant's own self defense. Long story short, allows plant to defend itself & pests don't like the environment. The frass is 2-2-2 & works as mild nutrient too. I can't say it is the only reason I have far less gnats this run but sure it has something to do with it. I've become a believer. 
