An adult dragon should get insects a couple times a week, with all he can eat greens every day. Never heard of the mini-mealworms but don't see any real value in getting something smaller than a regular mealworm when regular mealworms are not that great for dragons.
Silkworms are a very good stable insect as are butterworms, various species of cockroach such as lobster, hissing, deathshead and madacascar (though I think these are the hissing roaches, can't remember off hand).
Other than not eating his crickets, has he been eating his greens and is active? What are his poos like? Are they nicely formed without being excessively smelly or runny? Is he lathargic at all or does he seem to go to bed earlier than normal?
More details of his behaviour now and what he was like a few weeks ago, will make it easier to determine what is wrong. It isn't unnatural for dragons who reach a year old to slow down eating insects. He may even stop eating crickets knowing you have more tastier insects available, like silkworms or superworms.