Devra
We live on the Big Island.
We have found that the sow bugs eat our smaller seedlings. We don't plant things out until they are fairly big. Once the plants are big enough the sow bugs don't bother them. We have to keep the flats of seedlings up high enough or the sow bugs just climb up and help themselves. So that may your culprit.

Thanks for the reply. It's so nice to have advice from a fellow Hawaii gardener because so many of our gardening problems are unique to Hawaii.

I always use hay mulch over my beds and the sowbugs must love it because there are always tons of them. The strange thing is, I've always planted my tiny seedlings right into the midst of them without problems. Only in the last two months did the seedlings start disappearing.

Do you know if solarizing the soil with a sheet of clear plastic will kill the sowbugs?

I think solarization will either kill sow bugs or encourage them to move out of your beds and probably kill any eggs.
You are so right about the unique problems here.