452 



AN ECONOMIC ENTOMOLOGY. 



is to be applied freely around the base of the infested plants, and 

 probably, in part, depends for its effectiveness upon the large 

 amount of soap it contains. In any case, the earlier the appli- 

 cation is made the greater will be the effect. 



Carbolic acid in varying proportions is often added to mixtures 

 that are applied to tree trunks to prevent the entrance of borers. 

 It does no harm, at any rate, and there is some evidence that the 

 carbolated applications are more completely protective than are 

 those that contain no such material. 



Quassia, in the form of a decoction, has been recommended for 

 insects of various kinds, notably plant-Uce, but in my own ex- 

 perience the results have been unsatisfactory. 



Water, either hot or very cold, has some value as an insecticide ; 

 but the margin of safety is small. Boiling water is quickly fatal to 

 most insects and to vegetation as well. At one hundred and 

 twenty-five degrees Fahrenheit it is fatal to most insects and 

 safe on foliage generally ; at one hundred and forty degrees 

 Fahrenheit it is still safe on most foliage, but above that danger 

 begins, and, at one hundred and sixty degrees Fahrenheit it kills 

 all vegetation on which I tried it. At first blush this seems a 

 very simple remedy, but the practical difficulties of getting the 

 water on at the right temperature are so great that it is rarely 

 used, and then only when it can be applied at short range. 



Very cold or ice-water is effective against plant-lice under 

 some circumstances, and I have known of trees and bushes com- 

 pletely cleaned by one application. But our present knowledge 

 of the effect of cold on insects and plants is too small to make 

 practical recommendations possible. 



Repellents are those materials which are intended to prevent 

 insects from injuring plants that would otherwise be attacked, 

 and it is generally believed that it is the odor that repels. The 

 vapors of some substances, like turpentine, kerosene, naphthaline, 

 camphor, or the like, are absolutely poisonous when breathed, 

 and insects keep away because of the choking sensation pro- 

 duced. Therefore, lime or plaster with turpentine repel the 

 striped melon beetle, while tar-water will not. Other substances 

 have an odor so strong as to disguise that of the food plant so 

 that the insect does not recognize it ; therefore ground bone or 

 fish scraps will attract small rove beetles, but not melon beetles 

 to the melon hills so protected. 



