NATIONAL COUNCIL OF HORTICULTURE 25 



time no suitable insecticide is known for use on the peach during the 

 growing season. 



Fumigation. The destruction of insects by poisoning the air which 

 they breathe is practicable with several classes of pests, and has the 

 decided advantage over other methods of complete extermination. An 

 indispensable condition is that the object to be treated must be in an 

 air tight inclosure. Principally three fumigants are used, namely hydro- 

 cyanic acid gas, carbon bisulphide and sulphur dioxide. Fumigation with 

 hydrocyanic acid gas has become the standard treatment for nursery 

 stock, greenhouse plants, flour mills, warehouses, private dwellings, 

 etc. Gassing is also largely practiced in California in the control of 

 insects On citrus trees, and to a limited extent in Florida for the orange 

 white fly. A few years ago, the practicability of fumigating deciduous 

 fruit trees in the East for the San Jose scale was thoroughly tested in 

 Maryland, New York and Illinois, but the practice was never adopted 

 to any extent. 



Carbon bisulphide finds its greatest usefulness as an insecticide 

 for destroying insects in stored grain and cereal products. It is con- 

 venient to use and very effective. This substance is also employed in 

 the destruction of root inhabiting insects as the wooly apple aphis, cab- 

 bage root maggots and still to a limited extent against the phylloxera 

 in France, where at one time it was a very important remedy for this 

 pest. 



Sulphur dioxide, or sulphur fumes, has long been in use for the 

 destruction in rooms or dwellings of certain insect pests, but the bleach- 

 ing effect of the gas in the presence of moisture has made it much less 

 popular than the above two fumigants. Sulphur fumes are further 

 very destructive to plants, as witness the injury to vegetation in the 

 vicinity of smelting works. Nevertheless, sulphur dioxide will be more 

 or less useful in special cases. Thus it has been adopted by the North 

 German Lloyd Steamship Company, for the extermination in vessels of 

 insects, in grain, of rats and other vermin. 



PARASITIC AND PREDACEOUS INSECTS, AND FUNGOUS DISEASES. 



Introduced insect pests are almost invariably much more destruc- 

 tive here than in their original home, supposedly on account of the 

 influence of natural agencies which there operate to keep them reduced. 

 It is one of the resources of economic entomology to import from the 

 original home of an introduced pest any enemies which it may have,, 

 in the hope of bringing about its control. This sort of work had its 

 greatest inspiration in the notably successful importation from Australia 

 into California of the Vedalia to prey upon the cottony cushion scale 

 which threatened to destroy the citrus industry of that state. This 

 markedly successful instance of controlling a pest by one of its natural 

 enemies led to much effort of a similar character. Many importations 

 of predatory and parasitic species have been made, some with fair 

 success, but on the whole without marked effect on the abundance of 

 the injurious species. The introduction from China, the nativity of the, 



