Abstract o 1. Fed, starved and ligated Tenebrio molitor and Morimus funereus larvae were exposed to constant temperatures of 13 and 23°C. Over the period studied (3–5 days) the midgut proteolytic (MPA) and amylolytic activities (MAA) have been studied. 2. At the temperature favourable for the species ( T. molitor 23°C, M. funereus 13°C), MPA and MAA show cyclic changes both in fed and starved larvae. 3. At the temperature less favourable for the species (13°C), both in fed and starved larvae of T. molitor, the activity of both enzymes is maintained at about the same level and MPA shows long-term compensatory response. 4. At the temperature unfavourable for the species (23°C) in fed M. funereus larvae, MPA decreases to a negligible level, and cyclic changes are hardly noticeable. MAA maintains its cyclicity and shows compensatory response. 5. Under the effect of stress (unfavourable temperature, starvation, ligation) a short-term compensatory response occurs either at the level of MPA or MAA, dependent on the intensity of the stress.