Visualization of protein digestion in the midgut of the acarid mite Lepidoglyphus destructor

The ingestion of chromogenic or fluorescent substrates for protease detection enables the visualization of digestive processes in mites in vivo due to their transparent bodies. The substrates for protease detection were offered to Lepidoglyphus destructor, and the resulting signals were observed in specimens under a compound microscope. The protease activity was successfully localized using chromogenic substrates (azoalbumin, AAPpNA, SAAPFpNA, elastin-orcein, SA(3) pNA, ZRRpNA, ArgpNA, and MAAPMpNA) and fluorescent substrates (casein-fluorescein, albumin-fluorescein, AAPAMC, BAAMC, ZRRAMC, ArgAMC, and AGPPPAMC). No activity was detected using the keratin azure and BApNA substrates. In the mesodeum, trypsin-like activity generated by hydrolysis of the BApNA substrate was not observed, but the BAAMC substrate allowed the visualization of trypsin-like activity in food boli in the posterior mesodeum. The results indicate that cathepsins B, D, and G and cathepsin H or aminopeptidase-like activities are present in the midgut of L. destructor. Among these activities, cathepsin D-like activity was identified for the first time in the gut of L. destructor. All proteases mentioned are produced in the mesodeal lumen and form the food bolus together with ingested food, afterward passing through the gut to be defecated. The method used enables the visualization of protease activities in the gut of transparent animals.