Question
My dad has had catawba trees in his back yard for many years.  He used the worms for fish bait.  About 2-3 years ago, the caterpillers stopped forming on the trees.  Why could this be happening?  What would cause these worms to stop growing on these trees?  I know that a moth lays the eggs and the eggs develop into these caterpillars.  But why would they just stop producing on his trees?

Answer
Something has killed the source of the caterpillars either an insecticide spray or a natural virus. You need to re establish the population. Your best bet for starting the worms is to harvest eggs from a tree that is already established and attach them to your own tree. You can collect the caterpillars from another tree source and put them on your tree. They will turn into moths and lay eggs giving you a population next year. Try to get the caterpillars small so they will grow on this tree. Of course you will have to fore go fishing with them for this first year so they will develop for the next years.