Well, first off, you may have a hard time getting a gecko to recognize a f/t pinkie as food. Snakes do this because they have a very developed sense of smell and they are attracted to heat. My geckos have only eaten them live, and some of them simply refuse them no matter what. What type of gecko are you feeding? Perhaps with a lot of coaxing and jiggling and a VERY hungry gecko, you could get one to take it. Wouldn't hurt to warm it pretty well too. I feed pinkies to my leopard, tokay, and bent-toed geckos year-round, whenever I have extra available. They'll last at least 8 months in the freezer. You don't need to pre-kill them, just place them in a baggie in the freezer and their hearts will stop rather quickly. Good luck getting them to take it!
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?.?.? Leopard Geckos (eggs incubating)
1.1.1 Rhacodactylus ciliatus
2.5 Paroedura picta(eggsincubating)
1.1 Paroedura bastardi(eggs incubating)
1.1 Paroedura androyensis
1.1 Hemitheconyx caudicinctus
1.1 Cyrtodactylus irianjayensis
1.1 Gekko gecko
1.1 Pachydactylus turneri
1.1 Uroplatus henkeli
0.0.1 Hemidactylus turcicus turcicus
1.2 Teratolepis fasciata
Snakes
1.0 Blizzard Corn
1.0 Christmas corn
1.2 Reverse Okeetee corn (1 tang)
1.0 Ball Python