Normal and experimentally induced lysosomal activity in the larval fat body of Calliphora erythrocephala Meigen.

Acid phosphatase activity was demonstrated by EM-cytochemistry in 4 day old third instar larvae of the fly Calliphora erythrocephala Meigen, but not in younger stages. During larval development, the activity increased, reaching a maximum at the onset of pupariation. The reaction product was localized in Golgi vesicles and sacculi, in vacuoles and in protein granules of varying size and composition, confirming the autophagic character of the protein granules. Throughout larval development, the reaction product was restricted to membrane-bound structures and no indications of "free" cytoplasmic activity that might be related to cytolysis were found. Enzyme activity could be evoked by transplanting inactive fat body lobes into host larvae of a later developmental stage. High enzyme activity was induced in these transplants within 18 h. The sites of activity were roughly the same, but a portion of the activity in the transplants was found in the vacuoles. The induction could be inhibited by cyclohexamide.