You might have to mix the feed with some other things like the mosquito maggots or shrimp/krill to slowly get the smallies to take feed. You could also try bits of worms. The feed could be mixed with water, and mashed up a bit and that might help also.

Excerpt from Robert Crais' "The Monkey's Raincoat:"
"She took another microscopic bite of her sandwich, then pushed it away. Maybe she absorbed nutrients from her surroundings."