VEGETABLE INSECTS. 267 



fertilizers, the use of trap crops^ and the protection of the natural 

 enemies of insect pests all have their uses in reducing the loss caused 

 by insects, and often constitute the most effective means of keeping 

 some of the worst pests under control. 



Direct measures are those that kill by mechanical methods, 

 stomach poisons, contact sprays, or fumigation. 



MECHANICAL METHODS. 



Under this head comes the practice of collecting insects in order 

 to destroy them. This may be done by hand-picking, sweeping thein 

 into nets, catching them on various kinds of sticky surfaces, or by 

 catching them with trap lights. ]Many types of insects may be con- 

 trolled by these methods when no other way is feasible. 



STOMACH POISONS. 



The best known and most commonly used stomach poisons in 

 insect control are the various arsenical compounds. The most ef- 

 fective of these are discussed below. 



Arsenate of Lead. — This is an excellent poison, and is used more 

 extensively than any other arsenical in the control of leaf-eating 

 insects. It may be used either as a liquid spray or in the form of 

 dust and is effective both ways. For most leaf-eating insects it is 

 usually used at the rate of one pound of the powder form, or two 

 to three pounds of the paste to one hundred gallons of water. Ap- 

 plied in dust form it is very effective, and is peculiarly adapted to 

 Porto Rican conditions. It should be mixed with an equal part of 

 air-slacked lime, or dry, leached wood ashes, and may be applied by 

 shaking from a cheese-cloth bag, or by the use of a dust gun. 



Paris Green. — This is probably the best known of the arsicnicais 

 used in insect control, and it is a very strong and deadly poison. It 

 is excellent for use in the preparation of poison baits, but owing to 

 its tendency to burn delicate foliage, it is being displaced as a leaf 

 spray,' by the newer and safer arsenicals. 



Two other arsenicals that are coming into favor and are giving 

 excellent results in insect control are calcium arsenite and zinc 

 arsenite. Tbese both come iu the same form as arsenate of lead, and 

 may l)c used in a similar manner. 



CONTACT INSECTICIDES. 



The various concoctions of kerosene, tobacco, and soap are the 

 standard contact sprays and may be used against all soft-bodied 

 sucking insects. 



