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Journal of Experimental Biology 33,311-324 (1956)
Published by Company of Biologists 1956

Proteolytic Activity of the Midgut in Relation to Feeding in the Beetles Tenebrio Molitor L. and Dytiscus Marginalis L

R. H. DADD ¹

¹ Department of Zoology, Imperial College London

1. In Tenebrio secretion of protease occurs spontaneously after moult and adult emergence, and in response to feeding in the active larva and mature adult. Damp cellulose powder or water are effective in increasing secretion in the adult.

2. Since little enzyme is accumulated in the epithelial tissue when the total midgut enzyme is greatly increased, it is inferred that synthesis and discharge are interdependent. When synthesis (as indicated by comparatively high tissue enzyme) is accelerated, growth of the midgut epithelium occurs.

3. In starved Dytiscus protease is accumulated in the midgut tissue. Within one hour of feeding it is largely discharged into the crop. Protease recurs in the midgut tissue in a few hours, but remains low so long as the crop contains undigested material. When the crop is empty, discharge ceases and enzyme is again accumulated in the epithelium. Thus the process of discharge appears to be independent of synthesis.

4. The secretory mechanisms of Tenebrio and Dytiscus are discussed in relation to their feeding habits.