Quote: So, if the armour is chitin, what do you make a sword from?
Well, why won't you look at the other parts of those same giant insects that you are making your armor from? Their claws (lobster-like)? Their stingers (bee-like), etc?
Like the armor, I could imagine a sword made from a claw or spear made from a stinger won't look very conventional, but just imagine if you could take either the bottom or top pincer off from a whole claw that is very elongated, you could have something that looks like a curved katana-like blade with an array of thorns protruding from one side of that blade.
For the stinger-spear, you could have the poison-sacks hanging from sides of the spear head or within the shaft of the spear, and have some sort of trigger mechanism to release the poison whenever you make a thrust through armor.