Cytochemical demonstration of the effects of the acylureas flufenoxuron and diflubenzuron on the incorporation of chitin into insect cuticle

Abstract Flufenoxuron (“Cascade”) is a novel acylurea with acaricidal and insecticidal properties. It acts in a similar manner to diflubenzuron (DFB) by impairing chitin incorporation into insect cuticle. Chitin can be localised cytochemically using the lectin, wheat germ agglutinin (WGA), which binds specifically to N‐acetylglucosamine‐containing polymers. WGA adsorbed to monodisperse colloidal gold (WGA‐gold) was used as an electron‐dense marker for localising chitin in the cuticle of sixth‐instar Spodoptera littoralis. In the cuticle of control insects, the deposition zone and endocuticle were heavily labelled. In flufenoxuron‐ and DFB‐treated insects, only the endocuticle (formed before treatment) was labelled, the deposition zone being devoid of label. These results show that flufenoxuron and DFB act in similar manner in reducing chitin incorporation in the cuticle of S. littoralis.