Man's physical universe

xanabras

754 MAN'S PHYSICAL WELFARE

Over three million pounds of insect powder are used in the United

States each year. In 1940 we imported 12,000,000 pounds of pyrethrum

flowers. Many fly sprays consist of a solution of pyrethrins, the

active ingredients of pyrethrum in a petroleum fraction similar to

kerosene.

Every year about a million pounds of nicotine are extracted from

waste materials of the tobacco industry for use as an insecticide. It

is especially valuable as a contact insecticide in killing aphids.

Lime-sulfur spray used in the control of scale insects is prepared by

boiling together a mixture of sulfur, lime, and water. Recently developed

contact poisons are 4,6-dinitro-ortho-cresol and 2-cyclohexyl-

4,6-dinitrophenol.

Fumigants Are Also Used to Kill Insects.

Hydrogen cyanide gas, HCN, is used to fumigate warehouses and

sacked grain, although carbon disulfide is also effective for dry grain

and seeds. Carbon disulfide presents a serious fire hazard because of

its ready inflammability. A mixture of ethylene dichloride and carbon

tetrachloride, although it is a little more expensive for this purpose, is

not inflammable.

Paradichlorobenzene, so widely used as a deodorant, is also used to

kill moths in clothes, as well as borers in fruit trees. Methyl bromide

has been found to be an effective fumigant for the potato tuber moth,

the codling moth, and the Japanese beetle,

while dichlorethyl ether,

ethylene dichloride, hexachloroethane, ethylene oxide, and methyl

formate are used for other insects.

New invasions of insects are reported frequently, and new methods

of attack are being developed. One of the most destructive insect

pests is the termite, which gets into wood and eats the heart out of it

before it is detected.

Insect Repellents Are Greatly Needed.

In many communities where the expense of mosquito control is too

great, the home owners who have spent a great deal of money in

developing and caring for their lawns and gardens would welcome an

efficient repellent for mosquitoes that would permit them to enjoy

warm evenings in their yards.

A few repellents have been discovered. For example, butyl oxide

oxalate is a fair repellent, while tetramethyethylthiuran disulfide is

an excellent repellent for the Japanese beetle.

Adult houseflies are repelled by a mixture of diethylene glycol

monobutyl ether acetate and triethanolamine. A still better repellent

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