A group of insecticides based on esters of phosphoric acid. They enters the target’s body through the integument, thus acting as contact poisons. They may also be systemic, moving through the plant (or the host animal, e.g. livestock) and affecting the feeding pests. Organophosphates are water soluble and their activity is usually of short duration. They differ in their toxicity to mammals, some (e.g. parathion) being very harmful, whereas others (e.g. malathion) are only moderately toxic. Organophosphates inhibit the activities of the cholinesterase system.