Florida Agricultural Experiment Stations


 The most recent group of phosphatic materials to gain inter-
 est in the entomological world have been materials known as
 systemic poisons. These can be absorbed through either roots
 or foliage and taken into the tissues of the plant. There they
 serve as an insecticidal material against mites and other insects
 which feed upon the plants. One of these, known as OMPA
 (octamethyl pyrophosphoramide), has been described by Ripper
 et al. (19). Its structural formula is as follows:

 (CH3)2N 0 0 N(CH3)2

 P --0 -P
 / \

 (CH3)2N N(CH3)2
 Other closely related materials are in the experimental stage
 and some will undoubtedly soon be commercially available.

 Pharmacological Action of Phosphatic Insecticides
 All of the materials mentioned above have the same general
 physiological action upon warm-blooded animals. All may be
 classed as anti-cholinesterase agents. These chemicals destroy
 a material in the body which is known as cholinesterase. Ac-
 tually, cholinesterase is an enzyme which has to do with the nor-
 mal functioning of the nervous system (3). Cholinesterase is
 present not only in all warm-blooded animals but also in insects,
 and it is the destruction of cholinesterase in insects by the phos-
 phatic insecticides which gives these materials their insecticidal
 value. When cholinesterase is destroyed the nervous system no
 longer can function properly, symptoms occur and, if extreme,
 death ultimately may result. The actual function of cholines-
 terase is to destroy a substance called acetylcholine. In the
 presence of the enzyme cholinesterase, acetylcholine is broken
 down into choline and acetic acid:
 acetylcholine cholinesterase acetic acid + choline
 When a muscle contracts, the actual sequence of events is due
to an impulse being sent from the brain or nerve center along
a nerve to that muscle. At the point where the nerve ending
joins the muscle fibers the nerve impulse causes the liberation of
acetylcholine, and it is the presence of acetylcholine which causes
the muscle to contract. Normally there is cholinesterase present