Amazon, Home Depot, Lowe’s pretty much most home and garden stores will have it. It is an insecticide but not a bio pesticide. It’s not even put on the plant itself just on the top soil. The plant will just see it as a different type of soil essentially. Just looking at the Wikipedia article on what the composition is of diamacious earth will tell you this:
Diatomaceous earth consists of the fossilized remains of diatoms, a type of hard-shelled microalgae.[3] It is used as a filtration aid, mild abrasive in products including metal polishes and toothpaste, mechanical insecticide, absorbent for liquids, matting agent for coatings, reinforcing filler in plastics and rubber, anti-block in plastic films, porous support for chemical catalysts, cat litter, activator in coagulation studies, a stabilizing component of dynamite, a thermal insulator, and a soil for potted plants and trees as in the art of bonsai.