Attack of the Evil Monkeys From Hell
RTFA and it says:
Despite their new problems with the monkeys, it is a criminal offence to harm or kill any of them, so the besieged villagers must figure out a way to outwit the monkeys instead. So no, shooting or adding lithium/other chemicals to samples of crops to deter the monkeys (as another poster has suggested) is not a viable solution unless it becomes an extreme situation where criminal charges will not be applied to those that harm the monkeys in any fashion.
The only thing I can think of is to create shelters that the monkeys cannot access since they appear to be stealing the crops from within the houses as well as in the fields.