Im getting a medetteranian house geckos to rid roaches will borax kill the geckos.?

im getting a few medeitteranian house geckos to get rid of the german cockroaches i have in the house im moving into. if i use borax to help kill the roaches off will the gecko be harmed? will they walk through it and die? or eat the borax? or eat the roach balls im making mixed with sugar, flour, baking soda and borax? thanks to all who help.