I have a gecko that does not appear to be eating.

My leopard gecko has been eating both crickets and silkworms for the past five years. Then he would eat a silkworm and it appeared as if it came back up at some time during the night as it would be in his tank the next day undigested. No bowel movements have also been occurring. Switched to just crickets after this happened over 4 or 5 meals and there continue to be no bowel movements. Our second gecko - same age - is doing well. He is in a different tank that is next to the first geckos. Any idea what is happening or suggestions as to what I can do to fix this problem? Thanks.

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