I agree with both answers. In addition, temperature will affect metabolism and survival time (the higher the temperature, the higher the metabolic rate and lower survival time for the same amount of oxygen). To take into account insects are very tolerant to hypoxia (low O2) or even anoxia (no O2).
In storage containers, crevices and minute/micro space does exists which allows sufficient air passage for air traffic.If you fill such metal containers with water, you will see that small droplets of water oozing out there, which is indicator that they are not totally air tight.Air passes through such crevices and it is sufficient enough for meeting out requirements of insects esp. triborium spp or grain weevils etc.