10 
INSECTICIDES FOR EXTERNAL SUCKING INSEOTS (CONTACT POISONS). 
The simple remedies for this class of insects, such as soap, insect pow- 
der, sulphur, tobacco decoction, ete., are frequently of value, but need 
little special explanation. Some brief notes will be given, however, 
describing the methods of using some of these substances which are 
easily available and will often be of service, particularly where few 
plants are to be treated. The standard remedies for this group of 
insects, viz, the kerosene emulsions, resin washes, lime, sulphur, and 
salt wash, hydrocyanic acid gas, and vapor of bisulphide of carbon 
will be afterwards treated in the order mentioned. 
SOAPS AS INSECTICIDES. 
Any good soap is effective in destroying soft-bodied insects, such as 
plant-lice and young or soft-bodied larve. The soaps made of fish oil 
and sold under the name of whale-oil soaps are often especially valua- 
ble, but variable in composition and merits. A soap made with caustic 
potash rather than with caustic soda, as is commonly the case, should 
be demanded, the potash soap yielding a liquid in dilution more readily 
sprayed and more effective against insects. 
For plant-lice and delicate larvae, such as the pear slug, a strength 
obtained by dissolving half a pound of soap in a gallon of water is suf- 
ficient. Soft soap will answer as well as hard, but at least double 
quantity should be taken. 
As winter washes the fish-oil soaps have proved the most effective 
means Of destroying certain scale insects, and have been particularly 
serviceable against the very resistant San Jose scale. For winter appli- 
cations the soap is employed at the rate of 2 pounds to the gallon of 
water, and is applied hot with a spray pump as soon as the leaves fall 
in the autumn, repeating if necessary in the spring before the buds 
unfold. 
PYRETHRUM, OR INSECT POWDER. 
This insecticide is sold under the names of Buhach and Persian insect 
powder, or simply insect powder, and is the ground-up flowers of the 
Pyrethrum plant. It acts on insects externally through their breathing 
pores, and is fatal to many forms both of biting and sucking insects. 
It is not poisonous to man or the higher animals, and hence may be 
used where poisons would be objectionable. Its chief value is against 
household pests, such as roaches, flies, and ants, and in greenhouses, 
conservatories, and small gardens, where the use of arsenical poisons 
would be inadvisable. 
It is used as a dry powder, pure or diluted with flour, in which form 
it may be puffed about rooms or over plants. On the latter it is prefer- 
ably applied in the evening, so as to be retained by the dew. ‘To keep 
out mosquitoes, and also to kill them, burning the powder in a tentor a 
room will give satisfactory results. 
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