6-[1-Methyl-2-(4-phenoxyphenoxy)ethoxy]-3-pyridinol-d6 is an isotope labelled compound of 6-[1-Methyl-2-(4-phenoxyphenoxy)ethoxy]-3-pyridinol (M321115), which is a metabolite of pyriproxyfen (P998850); a pyridine-based pesticide used against a variety of arthropoda, in particular to protect cotton crops against whitefly.