What you don't say here is how old your crestie is. Hatchlings and juveniles need more protein than fruit and adults will generally eat more fruit (sexually mature females may tend to eat more protein than males to help with reproduction). Anyhow, if he's just a baby, try giving him the crested gecko diet to supplement his crickets and see how he does, and if he doesn't eat that (keeping in mind they have tiny tummies), add Herptivite to his crickets every other feeding.

Let us know how he does.