What broth are you using? I had trouble with crusty OP50 lawns when I
was growing up my OP50 stock in LB broth; one of the online discussion
boards noted this was common when using LB. My worms were extremely
unhappy with it, too. L1s that hatched on top of the crust would starve
sometimes. However, our worm labs at HSU generally have good results
using 3XD to grow OP50 for spotting plates.
Something else I thought of--perhaps you have too--if this is a recent
problem, could your lab have very low humidity from winter heating?
Good luck, and please post back if you solve the problem.
Graduate Student, Biology
Humboldt State University
1 Harpst St., Arcata, CA 95521