sick monarchs - Help!!!

[niemannim]

-I have hatched about 20 monarchs this fall in S.C. and have five so far
that do not have strength to fly no pesticides involved  as far as I can
tell.  They have no problems when they hatch, but don't have muscle
strength.  Any ideas? I'm on the East coast flyway and have been
raising  Monarchs and other large North American butterflies here for
twenty years and haven't ever seen this problem. Thank you for any
ideas.