Insects do not produce heat, i.e., they are "cold-blooded." Therefore, they will not likely produce a definable signature on the palate of the IR camera.
If they are within the wall cavity, there will be no signature at all from the insects themselves. IR can aid in detecting "voids" or "caverns" within the walls, but destructive testing will still likely be necessary to verify the source of the anomaly.
If your inspector is not using thermal imaging, you're not getting the whole picture. �
JPI Home Inspection Service
Santa Clarita CA