There are reports that Ukrainian civilians are poisoning Russian troops with pies. It may be worth noting that this tactic has a long history, and its use was honored by the Soviet Union when applied against Germans during WW2.
Assuming these reports are correct, and individuals who are not members of the national armed forces are using chemical agents to inflict harm on an occupying force via food products, is this tactic a breach of the Chemical Weapons Convention?
No. They are not engaging in combat under the Aditional Protocol of the Geneva Convention of 1949, because they are neither members of any (recognized or unrecognized) armed forces nor militia. They also don't spontaneously "take up arms to resist the invading forces, without having had time to form themselves into regular armed units".
They are also not unprivileged combatants, because they have not been combatants before, are not spies and are not mercenaries or child soldiers. They also are not taking a direct part in combat.
As a result, they are mere civilians and to be treated as such.
Civilians are not states and their militaries. Only states and military are bound by the CWC.
As a result, no breach of the CWC happens if one of the Occupied People leaves out these PIEs, which are then looted and consumed by the occupying forces. Only civilian charges are legal and retaliation against the Occupied People would be another war crime against them: Looting already is a war crime. What charges can come is dependant on how the PIEs were stored before:
If the PIEs are instead given to the occupying forces knowing they are PIEs, the whole situation changes: suddenly we got a solid charge of [attempted] murder. This is a capital crime, and as a result, the occupying forces could prosecute. In case the occupied (NOT occupying!) country had the death sentence they could execute the perpetrator after a trial. Shooting the perpetrator on the spot, however, could be a war crime. But still, the CWC is not touched as the Occupied People did not become combatants: even when committing single acts, it takes active hostilities, which are defined as combat, to become a combatant. As they are not part of the military, not even organized militia, they can not be held up to the CWC, which by itself only binds the state and their military.
Only if the Occupied People would form a regulated militia, they would not be allowed to leave PIEs.
No, poisoning is just like stabbing with a knife, strangling, shooting with a gun, and all would have been done by civilians acting in very justified self defence as several hundred brutally murdered civilians in the Ukraine would easily prove.
Also, putting seeds into the pockets of dead enemy soldiers so they can do something useful after their death doesn't count as biological weapons.
