The quantities of energy reserves and their utilization were examined in adults of three strains of Tribolium castaneum (Herbst) before and during exposure to two modified atmospheres. It was shown that a strain selected for resistance to high carbon dioxide (CO2) content (HCC) contained significantly greater triacylglycerol (TG) reserves than a strain selected for resistance to low oxygen (O2) concentration (LOC) and an unselected strain. During exposure to HCC (65% CO2, 20% O2, balance nitrogen), the major energy sources were TGs, most of which were consumed during exposure; TG utilization by the unselected strain was more rapid than that by the HCC-selected strain. During exposure to LOC (0.5% O2, 99.5% nitrogen), TGs were also utilized, but to a lesser extent, revealing an indication of more attenuated mobilization of energy reserves. Here, too, TG utilization by the unselected strain was more rapid than by the LOC-selected strain. The function of TGs in enabling the insects to maintain their water balance during exposure was considered. Concentrations of polysaccharides and glucose were low in all strains and although they decreased during exposure to MAs, their contribution to metabolic energy supply during exposure was small. (C) 2000 Elsevier Science Ltd.