236 Appendix. 



It is the purpose of this bulletin to give brief directions for the preparation 

 of the most important insecticides and fungicides that have been tested by ex- 

 periment station w^orkers and found useful, prefacing these directions by such ref- 

 ♦^rences to the nature of insects and fungi as may be necessary to an under- 

 standing of the general principles which underlie the successful use of the various 

 compounds mentioned. 



INSECTS AND INSECTICIDES. 



To understand the general principle which underlies the selection of the 

 proper remedy to be used for any particular insect, one has only to know that 

 practically all insects may be divided into two great groups. 



Group I. — This includes all Insects that have biting mouth parts — mandibu- 

 late insects — and which actually chew and swallow the tissues of the plant or 

 other substance upon which they feed. Grasshoppers, caterpillars, flea-beetles, 

 striped cucumber-beetles, codling moth larvae, etc., are good examples of this 

 group. 



Group II.- — This includes all insects with beak-like sucking mouth parts — 

 haustellate insects — which pierce the plant or animal upon which they feed and 

 suck up its juices or blood but neither chew nor swallow any of the structural 

 tissues. The apple-tingis, woolly-aphis, hop-louse, green apple-aphis, black cherry- 

 aphis, San Jose scale, etc., are good example of this group. 



In general, insects which belong to group I may be poisoned by sprinkling 

 or dusting the surface of the plant upon which they feed with some poisonous 

 substance ; but insects which belong to group II cannot be so poisoned since they 

 securetheir food from beneath the surface and cannot be made to eat the poison. 

 They must be destroyed by gases, washes, or other substances which act externally 

 upon their bodies. 



All insecticide substances may therefore be arranged into two general groups. 



Group I — Food Poisons. — This group includes, principally, the various arsen- 

 icals, such as Paris green, London purple, Scheele's green, arsenite of soda, ar- 

 senate of lead. etc. These poisons are all valuable against insects which belong 

 to group I and feed exposed upon the surface of plants but are practically value- 

 less against those of group II. 



Group II — Contact Insecticides. — This group includes a great variety of sub- 

 stances which act externally upon the bodies of insects either as mechanical 

 irirtants or caustics, or to smother them by closing their breathing pores, or to 

 fill the air about them with poisonous gases, or simply as repellants. Soap, sul- 

 phur, tobacco, insect powder, hellebore, kerosene, kerosene emulsions, crude pe- 

 troleum, the lime-sulphur-salt wash, resin washes, hydrocyanic acid gas, and car- 

 bon bisulphide are some of the most valuable insecticides of this group. These 

 are used successfully not only against sucking insects but many of them are also 

 used against biting insects when for any reason it is undesirable to use poisons ; 

 or when it is impossible to apply poisons directly to the food supply, as in the 

 case of insects which work beneath the surface of the soil, or as borers or miners 

 in wood, leaf or fruit, or in stored products, or as animal parasites, or household 

 pests. 



FUNGI AND FUNGICIDES. 



A fungus is a plant as truly as is the apple tree, the prune tree, the wheat 

 plant or any other plant upon which it may be growing. It differs from the 

 common plants essentially in being much more simple in structure and in being 

 devoid of chlorophyll — the green coloring matter of plants. Its seeds, which are 

 called spores, are more simple and very much smaller than the smallest seeds 

 of our common plants and are produced in almost inconceivably great numbers. 

 The vegetative portion of the fungus, the part which, in a sense, corresponds 

 to the roots, stems and leaves of ordinary plants, the part which absorbs the 

 food materials and eventually produces the spores, consists of a mass of more 

 or less branched, white or colorless, and very minute threads and is called the 

 mycelium. 



