relaxants, and that several others (again including malathion) markedly increase the sleeping
time of barbiturates....
In Greek my thol ogy the s orceres s Medea, enraged at being s upplanted by a rival for the
affections of her hus band Jas on, pres ente d the new bride with a robe pos s ess ing magic
properties. The wearer of the robe immediately suffered a violent death. This death-by-
indirection now finds its counterpart in what are k nown as ‘s ys temic insecticides ’. Thes e are
chemicals with extraordinary properties which are used to convert plants or animals into a sort
of Medea’s robe by making them actually pois onous. This is done with the purpos e of killing
ins ects that may come in contact with the m, es pecially by s ucking their juices or blood.
The world of s ys temic ins ecticides is a weird world, s urpas s ing the imaginings of the brothe rs
Grimm—perhaps mos t closely akin to the cartoon world of Cha rles Addams. It is a world where
the enchanted f ores t of the fairy tales has become the pois onous fores t in which an ins ect that
chews a leaf or sucks the sap of a plant is doomed. It is a world where a flea bites a dog, and
dies becaus e the dog’s blood has been made pois onous , where an ins ect may die from vapo rs
emanating from a plant it has never touched, whe re a bee may carry pois onous nectar back to
its hive and pres ently produce pois onous honey.
The entomologis ts ’ dream of the built-in ins ecticide was born when worke rs in the field of
applied entomol ogy realized they coul d take a hint from nature : they found that wheat growing
in soil containing sodium selenate was immune to attack by aphi ds or s pider mites. Selenium, a
naturally occurring element found s paringly in rocks and s oils of many parts of the world, thus
became the first systemic insecticide. What makes an insecticide a systemic is the ability to
permeate all the tissues of a plant or animal and make them toxic. This quality is possess ed by
s ome chemicals of the chlorinated hydrocarbon group and by othe rs of the organophos phorus
group, all synthetically produced, as well as by certain naturally occurring substances. In
practice, howeve r, mos t s ys temics are drawn from the organophos phorus group becaus e the
problem of res idues is s omewhat les s acute. Sys temics act in other devious ways. Applied to
s eeds , either by s oaking or in a coating combined with carbon, they exte nd thei r effects into the
following plant generation and produce s eedlings pois onous to aphids and othe r s ucking
ins ects. Vegetables s uch as peas , beans , and s ugar beets are s ometi mes thus protecte d. Cotton
s eeds coated with a systemic insecticide have been in use for some time in California, where 25
farm labourers planting cotton in the San J oaquin Valley in 1959 were s eized with s udden
illness , caus ed by handling the bags of treated s eeds. In England s omeone wonde red what
happene d when bees made us e of nectar from plants treated with s ys temics. This was
investigated in areas treated with a chemical called s chradan. Although the plants had been
s prayed before the flowers were forme d, the nectar later produced contained the pois on. The
res ult, as might have been predicted, was that the honey ma de by the bees als o was
conta mi nated with s chradan.
Use of animal systemics has concentrated chiefly on control of the cattle grub, a damaging
parasite of livestock. Extreme care mus t be us ed in order to create an ins ecticidal effect in the
blood and tis s ues of the hos t without s etting up a fatal poisoning. The balance is delicate and
government veterinarians have found that repeated small doses can gradually deplete an
animal’s s upply of the protective enzy me cholines teras e, s o that without warning a minute
additional dose will caus e pois oning.
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