The following Pesticide guns will become available when you reach Rank 8 of the corresponding Armour class. You can only reach Rank 8 by playing under the Inferno difficulty setting.

Trooper Armour Class:
Pesticide Cannon (Tier 8 Rocket Launcher).

Battle Armour Class:
Pesticide Mortar (Tier 8 Grenade Launcher).

Tactical Armour Class:
Pesticide Missile (Tier 8 Missile Launcher).

Jet Armour Class:
Pesticide Rifle (Tier 8 Sniper Rifle).