The trouble with tracking political dissidents with radio collars is that they flat-out refuse to wear them. Insects, too, are impossible to track with radio collars, but for a different reason. They are too heavy for the insects to carry. So some clever scientists have adapted harmonic radar to the tracking of bees. Click here for the full story.
Bees are fairly burly, as insects go.
To track butterflies, an even lighter device was needed. It's a fascinating tale. Go to the library. Find the February 1997 issue of Discover magazine. The pictures are very impressive.