What geographical area of earth has no insects?
According to the geographical/astronomical definition of the tropics, that part of the earth is not changing in size. But in terms of the meteorology involved, the warm band around the earth is beginning to expand beyond the traditional boundries. This is thought to be an effect of global warming, which is underway.
It gets stuck on the insects' hair and wears away at the shells, leaving it dehydrated. It also gets eaten, and cuts up the diaphragm and innards of the insect. Actually diatomaceous earth does not cut up the innards, just the outter shell. The insect is aware that the edges of the DE is very sharp so that is why they leave the area or plant it is on.