Early in District 9, when Wikus and other MNU personnel enter the slums where the Prawns live, we see some Prawns, apparently prepared to resist the relocation, carry normal rifles.
But we also see the Prawns trading their extremely valuable weapons for tins of cat food. I can see plot-wise the value of the Prawns not using their own highly advanced weaponry against the humans (although this does eventually happen) because it would be a ridiculously unbalanced fight.
Is it explained in perhaps a novelization why this is? Could it be that not all Prawns have the right DNA to use such weapons or is it possible that by the point of the relocation that all weapons have already been sold or confiscated?