It says in Shulchan Aruch (OC Siman 629 Sif 3) that one may cover a Sukkah with "chitzim" (arrows) that don't have a "beis kibbul". However if they do have a "beis kibbul" then it's not valid for scach. "Beis kibbul" basically means some opening or cup that can be a receptacle, and can therefore be made tamei (impure). The Magen Avraham writes (ad loc., Sif-Katan 2) that "kanim" (rods) that have a "beis kibbul" are valid, since they weren't made to be "m'kabel". Seemingly this is similar to our bamboo sticks or the like that people use for scach. However, what about if one would put some sort of "chomer" (a poision or the like) used to kill bugs inside of the sticks? I'm not talking about a spray or something of the like – rather something that has to it mamoshos (substance) that sits in the sticks and helps to kill the bugs. Even though these kanim, like the M"A says, weren't made to be a beis kibbul, since l'maseh (practically) they are being used in such a way, does this invalidate it for being scach?