Rubber septa is used in

Rubber septa are used in Pheromone trap.
A pheromone trap is a type of insect trap that uses pheromones to lure insects. Pheromone traps are used both to count insect populations by sampling, and to trap pests such as clothes moths to destroy them.
Rubber septa are most commonly used to seal medicinal vials containing either a liquid or freeze-dried solid (which is then liquefied in water or other substance). The medicine is drawn from the vial using a needle, then injected.