Did you freeze them or anything before you put them in? I've found if you freeze things for about oh, 20-30 minutes before you put it in it helps. It breaks down the cell walls or something along those lines. I got in fresh mulberry leaves a week or so ago, and wanted to feed one right away. I put it in the freezer for 15 minutes, then put it in the tank. They were on it within 2 minutes. Other than that, they may just not like them. Like people they can have different tastes. Or if you're feeding a high protein food they may be less likely to go for it.