Destruction of peritrophic membrane and its effect on biological characteristics and activity of digestive enzymes in larvae of the Indian meal moth, Plodia interpunctella (Lepidoptera: Pyralidae)

The mid gut in insects is usually lined with a peritrophic membrane (PM), which protects it from microbial infections and physical contact with ingested food. Calcofluor is an optical brightener that has strong chitin-binding properties, which disrupt the chitin-protein structure of PM. In this study, we investigated the effects of calcofluor on the structure of the PM, activity of some common digestive enzymes and biological characteristics of the Indian meal moth, Plodia interpunctella (Lepidoptera: Pyralidae). Twenty hours after feeding on a calcofluor-containing diet, the PM was completely eliminated. We recorded significant effects of calcofluor on the activity of digestive enzymes in the mid and hindguts of larvae. In both these regions of the gut, in particular, there were significant increases in the activity of α-amylase, α-galactosidase and trypsin. The activities of α-glucosidase and β-glucosidase in the midgut of treated larvae were lower than in the control, but were significantly higher in the hindgut of treated larvae. The larvae that fed on on calcofluor for 20 h, took longer to complete their larval and pupal stages, were lighter in weight and fewer reached maturity and laid fewer eggs. Results of this and previous studies highlight the crucial role of PM in enzyme recycling and digestion. PM disruption may negatively affect insect development on the one hand, by decreasing the efficiency of food digestion and, on the other, by increasing the costs associated with an increased enzyme demand and disrupted enzyme recycling mechanism.