You could try a different cricket food. Buggrub is only one in a thousand brands. It might just not be palatable to the crickets.
If your froggy doesn't like the black crickets, go back to the brown. If you first fed the black crickets to him when they were dusted, maybe he is associating the dust with the black crickets?
Food is a good size if it is the size of the length between your frog's eyes.
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~Sara~
5 ball pythons
1.0 Black-lined plated lizard (Lizzy Butt)
0.1 Burmese Python (Pixil)
lots of Rats
1.1 Dogs (Ozzie and Mandy)
0.1 Cat (Isis)
0.0.1 Synodontis Catfish (Big Spotty Fish)
0.1 Convict Cichlid
0.0.1 blood parrot cichlid
0.0.1 African Featherfin Catfish