The site where the toxin usually binds in the insect becomes modified to reduce the insecticide's effects. This is the second most common mechanism of resistance. The site of action has been altered to decrease sensitivity to toxic attack. Alterations of amino acids responsible for insecticide binding at its site of action cause the insecticide to be less effective or even ineffective. The target of organophosphorus (malathion,fenitrothion) and carbamate (propoxur, sevin) insecticides is acetylcholinesterase in nerve synapses, and the targets of organochlorines and synthetic pyrethroids are the sodium channels of the nerve sheath.