Help me save my pine
 

The house we just bought has a small (3.5 ft. tall) long leaf pine in
the front yard. Some kind of worm is eating the needles on the tree and
has already eaten the top third of the tree. I've picked them off and
killed them only to have more reappear a week later. These worms are
about an inch long and are green. Does anyone have any idea what they
are and what I can use to keep them off this tree?

Thanks for the help,
Ron