Start with the reassurance the question usually needs: a crested gecko that eats a complete powdered diet reliably is not missing out nutritionally. Modern complete powdered diets for this species are formulated to cover its protein, calcium, and vitamin needs on their own, because crested geckos eat fruit and insects opportunistically in the wild rather than living on insects alone. Live insects are enrichment and variety, not a requirement you must somehow force past a refusal.
Confirm the powdered diet is doing the whole job
Check three things before worrying about insects. First, the diet must be a complete crested gecko diet, mixed fresh to a smooth consistency and replaced on its normal schedule, usually every day or every other day, rather than a fruit puree or a homemade mix, which would not be complete. Second, the gecko should be holding a steady weight with a plump tail base and clean sheds, which you can only judge if you weigh it, so weigh monthly on a small scale and note the result. Third, the enclosure should sit in the low-to-mid 70s Fahrenheit (around 22 to 25 degrees Celsius) with regular misting, because a gecko that is too cool or too dry often eats less of everything.
If a gecko on a complete diet is gaining or holding weight, shedding cleanly, and active at night, its refusal of insects is a preference, not a warning sign.
Offer insects the way this species actually hunts
Crested geckos are dusk and night feeders, so an insect offered under bright light at midday is easy to ignore. Offer one or two small insects in the evening, sized no wider than the space between the gecko's eyes. Try a different feeder type before concluding it refuses all insects, because a gecko that ignores crickets may strike at small roaches, and the movement pattern is what triggers the response.
Tong-feeding lets you place the insect in front of the gecko and withdraw it if there is no interest. A smooth-sided feeding cup works for geckos that prefer to hunt alone, provided you check it later the same evening. Remove uneaten live insects rather than leaving them loose overnight, because loose crickets can bite a resting gecko and because uneaten insects foul the enclosure. Dust any insects you offer lightly with calcium powder, as you would for any insect feed, and never offer wild-caught insects, whose parasite and pesticide risks are not worth the variety.
Tactics worth one attempt each
Smearing a little of the powdered diet on an insect sometimes transfers a familiar taste to a new food. Offering an insect immediately after the gecko has licked diet from your fingertip can also work, because the feeding response is already switched on. Presenting a smaller insect than you first tried is worth doing, since oversized prey is a common reason for refusal that looks like disinterest.
Stop there. Do not withhold the powdered diet to make the gecko hungry enough to hunt, because a gecko that relies on that diet should never be starved into a different one, and a healthy refusal will not be cured by hunger. Accept the preference if two or three calm attempts fail, and revisit it after a shed or a season change, when appetites often shift on their own.
When refusal becomes a vet question
Book a vet visit if the gecko also stops eating the powdered diet, loses weight across two monthly weigh-ins, develops a wavy or soft-looking jaw or limbs, or becomes lethargic during its usual active hours. A vet can investigate whether appetite changes point to a wider health issue, which is a different question from insect preference alone. Bring your weight and feeding notes, because a short written record makes that conversation far more useful. KinsLe's Care Teams keeps those evening feeds and monthly weigh-ins assigned to named helpers with completed tasks timestamped, so the crested gecko's record stays reliable enough to show a vet.