282 



THE AGRICaLTURAL NEWS. 



Septemiskr 3, 1910. 



INSECT NOTES, 



INSECTICIDES. 



Dniing the past few years there Jias been a great increase 

 in the amount of materials used in the West Indies for the 

 control of insect pests. This has been partly dne to a better 

 knowledge of the means of controlling pests which were 

 formerly known, and partly to the revival of the cotton indus- 

 try, which has brought to notice several not previously recog- 

 nized. 



The pro[ier use of insecticides depends u[ion a knowledge 

 of the life-history and structure of ,ho insects to be dealt with. 

 Insects which have mouth parts suited for biting, may be 

 controlled by means of stomach poisons, which being eaten 

 with the food, cause the death of the insect by their poisonous 

 action. Many .soft-bodied insects, on the other hand, and 

 especially insects which have mouth parts fitted for piercing 

 the plant tissues and sucking the juices from them, may best 

 be destroyed by the use of poisons which kill by coming 

 into contact with the surface of the body. 



Insects which bore into the tissues of plants or live 

 amongst seeds, grain, flour and similar materials may some- 

 times be destroyed by the use of a fumigant, so applied that 

 the poi.sonous fumes or gas will be able to reach the insects 

 and act upon them. In addition to these substances, which 

 actually kill the insects, there may also be considered those 

 which are useful from their action of repelling the insects. 

 Mosquitos, borers, and many household pests may lie dealt 

 with by this means. 



In considering the diflferent kinds of poisons, it may be 

 well to note in a general way the insects for the control of 

 which each kind is useful. 



STOMACH I'oisoNs. Tliese may be used against all kinds of 

 leaf-feeding caterpillars, cut worms, mole crickets, cockroaches, 

 gras.shoppers, ants and white ants. For the control of cater- 

 pillars, a suitable poison may be dusted or sprayed on the 

 surface of the leaves. Cut worms may be killed by mi.xing 

 the poison with an attractive food substance and placing it 

 where they will find it. The same method api)lies to mole 

 crickets, cockroaches, grasshoppers, etc. 



The most important stomach poisons available for insecti- 

 cide purposes are those which contain arsenic in one form or 

 another. The best known of the arsenical poisons in the 

 West Indies is Paris green, whicli has been used to such a 

 large e.xtent in the control of the cotton worm. Other arseni- 

 cal poisons are London purple, arsenate of lead, arsenite of 

 lime and white arsenic. Corrosive sublimate, which is 

 a compouiid of mercury and chlorine, is a very powerful 

 stomach poi.son: but it is not adapted to general agricultural 

 use because of its injurious effect on tender plant tissues; it 

 is the poisonous part of the solution used for the preservation 

 of books against the attacks of insects. (See A'/riraftm-a/ 

 News, Vols. I, p. 140; II, p. 42; VI, p. 346; VIII, p. 367.) 

 Boracic acid may be counted a stomach poison, since it pro- 

 duces death when eaten by cockroaches; and plaster of Paris 

 may also be considered urderthis head, for it may be lui.xed 

 with flour in such a way as to be attractive to cockroaches 

 and cause their death, when, under the influence of moisture, 

 it hardens in the dige.stive tract of the insect. 



Paris green is sold in the form of a very fine powder, 

 which is a compound containing arsenic, copper and acetic acid. 

 It was originally manufactured as a colour, but is now made 

 on a large scale for insecticide purposes. Paris green may be 

 used dry, or as a .spray. It.is used dry in \arying j)roportion.s, 



mi.vcd with air-slaked lime, flour or other substances; or by 

 itself. When used as a spray, it is generally employed at the 

 rate of 1 tb. to |.50 gallons of water. This proportion may 

 be varied to make the mi.\ture either stronger or weaker, 

 according to the plants to be s[irayed. Paris green in water 

 sometimes has a burning ettect on the leaves of plants, and to 

 offset this, quicklime should be added to the mixture at the 

 rate of about 2 lb. of lime to each pound of Paris green. 



London purple is similar in its effect to Paris green, and 

 may be used in the same manner. The proportion of arsenic, 

 in London purple, is rather smaller than that in Paris green, 

 and consequently more of the poison would be required. 

 U.sed as a spray, London purple will need to be treated in 

 exactly the same way as Paris green. Arsenate of lead is 

 generally sold in the form of a heavy paste, which is only 

 available for use as a spray. It is rather .slower in its action 

 than Paris green or London purple, but does not burn the foli- 

 age, even of delicate plants, and on this account it may .safely 

 be use<l even at strengths of 10 to 20 ft), per 100 gallons of 

 water. AVithin the past few years, arsenate of lead has been 

 placed on the market in the form of a powder, which may be 

 applied dry, as a dust. 



Arsenite of lime and white arsenic are more likely to 

 burn the leaves of plants th^n any of the otlier arsenical 

 poisons mentioned, and consequently have a somewhat limited 

 use. They may be employed in the destruction of cut 

 worms, ants, gras.shoppers and termites, in the form of a bait 

 in which the poison is mixed with some attractive food 

 substance. 



Corrosive sublimate, used as book poison, is pre[)ared by 

 mixing 1 oz. of this material with 1 oz. of carbolic acid in 2 

 parts of methylated spirit. The corrosive sublimate enters into 

 solution, and when the mixture is applied to the surface of 

 books, especially those in cloth bindings, it gives very good 

 protection against the attacks of cockroaches and similar 

 pests. 



Boracic acid is u.sed as an insecticide mixed with equal 

 parts by weight of sweet chocolate, molasses or some similar 

 substance, for the destruction of cockroaches. This mixture 

 is not poisonous to cats, dogs and fowls; but is a very efficient 

 remedy for cockroaches. Plaster of Paris mixed with flour 

 will also be eaten by cockroaches if placed in their haunts 

 and, if water is available for the insects to drink, proves 

 a very good insecticide. The plaster of Paris, moistened by 

 water, hardens in the digestive tracts of the insect.s, and in 

 this manner kills them, as has been explained. 



CONTACT roisoNS. Thesc are found useful for the con- 

 trol of scale insects, plant lice, cotton stainers and mosquito 

 larvae. In the case of the first three of these, it is necessary 

 that the insecticide should come directly into contact with 

 the bodies of the insects. In the case of mosquito larvae, for 

 instance, when kerosene is ai)plied to the surface of the water 

 in which they live, the insects are killed by absorbing the 

 poison, as well as by suffocation. 



Contact poisons usually depend for their insecticidal 

 properties on the action of the soaii, oil or ro.sin which is con- 

 tained in them. Recently, spraj' mixtures containing lime, 

 salt or sulphur, or some form of ar.senic have also been used. 

 Kerosene eiuulsion, whale oil .soap and rosin compound are 

 well-known examples of contact poisons which have been used 

 in the West Indies with good results. The directions for 

 prejiaring them for u.se may be found in various publications 

 of the Imperial Department of Agriculture*. The lime, silt 

 and sulphur mixtures are more especially suitable for use in 



*.See. .S'c.Jc Insects nf the Li'esKv AiiiVhs, Pamphlet series 

 Nos. 1-t and 22. 



