Use Glad Press'n Seal sealable plastic wrap to ""plug"" vials in the fly kitchen, leaving the real plugging to be done when flies are on the vials. The application of this sealable plastic wrap not only saves time in the food preparation facility , but also in the lab since the vial user does not need to unplug each vial prior to use. The seal has been found to significantly increase the shelf life of prepared fly food.