When the air which passes over or through a product changes the temperature and humidity of that product, the mites and insects react to it. Air also has other properties that affect insects. Carbon dioxide has a concentration at 0.03 % in air and if it rises to a few percent, the air is toxic to humans and other warm-blooded animals. Mites and insects can tolerate much higher concentrations. One must maintain a carbon dioxide concentration of 60 % at a minimum of
27 ° C for at least four days just to achieve a 95 % extermination of the current storage insects. Efficiency also depends on the metabolism of the insect phase. Resting phases such as eggs and various moulting phases can withstand more than other insect phases. A moderate to high carbon dioxide content in the air will increase the effect of treatments with insecticides or poison gas.
Nitrogen has a poor effect. Nitrogen concentration must be 99.5 % and the duration must be at least tripled at the same temperature as before, to achieve any effect at all. Insects can live in oxygen deficient atmospheres. In contrast, the combination of a high concentration of carbon dioxide and an oxygen level beneath 2 % has proven quite effective to kill pests after some time. As everyone with gastight silos knows, the disadvantage of this method is that it only works as intended if you are very careful to keep the oxygen percentage low in the entire storage period.
Low air pressure has no significant effect on insects. They simply stop their activity as long as the low air pressure lasts, and it is only if the low air pressure has secondary effects in the form of excessive water loss from the insect, that you can count on them to take permanent damage after short periods at low air pressure. Large and rapid pressure changes in the air like vacuum packaging of goods is not good for insects, but it does not necessarily kill them. Very small pressure changes in the atmosphere in the form of low pressure may cause small changes in behaviour, for example, with granary weevils, wherein the percentage of insects that exhibit chaotic behaviour appears to vary with the pressure changes.