An aerosol can containing insect extermination gas. It can be wielded as a weapon, and when sprayed in an enemies face it will cause them to stagger backwards.
David can convert this into a more deadly weapon by combining this with a Lighter using a piece of Vinyl Tape. This will create the Flame Spray.
Pesticide Spray (×9) - Behind the wall panel at the top of the stairs, next to the door leading to the supply room. This wall panel can only be opened by David.
Pesticide Spray (×2) - Inside the left-hand locker on the southern wall of the room with the nameplate of Jim. This locker can only be opened if you are playing as Jim.
Pesticide Spray (×9) - On the ground near the stairs in the passage behind the movable bookcase. You need to push the switch on the wall next to the bookcase in the main room to reveal the passageway.