monarch problems

[KTL6]

I have been raising butterflies for about 2 years. I have had the weak
butterfly problem with no answers, but I also have another problem.  The
moanrch chrysalids appear a two tone green.  When they approach the time to
emerge, the chrysalids either turn mushy or the butterfly is weak and can not
fully emerge from the chrysalis.  Their bodies are not completely black toward
the rear , but rather a yellow/green.  I have also had a couple of caterpillars
die in the middle of pupating.  I started keeping a journal last year.  I find
that this problem occured last year at the same time in approxomately the same
numbers.  I use glass containers for raising the caterpillars.  thanks.