Insects are known to feed on very dry substances (such as seeds, hair & flour) without the need to drink water. How do insects remain hydrated with nothing to drink? Metabolic water.
In the process of turning sugar into energy, cells add oxygen to sugar to produce energy, carbon dioxide and water. As long as the insects have adequate supply of food and oxygen, they can produce their own water. The metabolic water is very efficiently retained and the amount of water produced is greater than the low level rate of water loss from the insect.
Hermetic storage that blocks movement of oxygen into a package, will kill insects inside the package. Once the insects inside the package use all the available oxygen, energy metabolism and water production cease. The insect dies from dehydration and the inability to produce water. Hermetic technology, such as PICS bags, can be used to protect food against insect damage while in storage. Grains can be stored hermetically using cheap plastic that is widely available and works better for some applications than pesticides.