ECONOMIC ENTOMOLOGY 175 



resulting in the formulation of the general principle of the utility of 

 stomach poisons. This has led to the investigation of many materials 

 from the standpoint of their value as insecticides, together with deter- 

 minations of their relative efficiency in different cases, how to control 

 their effects and how they may best be applied, resulting in the develop- 

 ment of spray pumps, nozzles and spraying apparatus in general. 



Closely following the discovery of stomach poisons as insecticides 

 came that of contact poisons for sucking insects, for though Harris 

 had suggested soap solutions in one or two instances the general prin- 

 ciple had until this time failed to be formulated. Here, too, investi- 

 gation progressed rapidly, developing different materials as contact 

 insecticides varying in strength and in their range of application until 

 this field may now be considered to have been well explored. 



Fumigation, as a method of control, during all this time remained 

 almost unnoticed, its limitations being apparently so great, and the 

 fumigants themselves being so mild as to give little promise of results 

 of value. But during the last twenty years the utilization of gas- 

 tight tents, and of hydrocyanic acid gas and carbon disulfid has shown 

 that this method of control has a far wider range of applicability than 

 was formerly supposed, and fumigation is now perhaps as well devel- 

 oped and its possibilities as thoroughly understood as is the case with 

 stomach and contact poisons. 



During the last three quarters of a century the ravages of insects 

 have so greatly increased as to attract much attention to the subject, 

 and many persons have become specialists in economic entomology. 

 Numbering less than half a dozen in 1850, we now find more than five 

 hundred workers, each year publishing thousands of pages on the 

 results of their investigations. Large societies now hold regular meet- 

 ings at which the problems of economic entomology are discussed; and 

 the subject, once of little importance and of which almost nothing was 

 known, has now become a large and important branch of applied science, 

 with more positions waiting than there are competent persons to fill 

 them. 



The rapid increase in the losses caused by destructive insects, which 

 has focussed so much attention on economic entomology is difficult to 

 state accurately in figures, but was estimated in the report of the 

 TJ. S. Commissioner of Patents (then in charge of the agricultural 

 work of the government) in 1850, to be at least twenty millions of 

 dollars, while other estimates of that period made in terms of the total 

 crop value placed the loss at about ten per cent. Since that date con- 

 ditions have changed materially and are continuing to change for the 

 worse. The development of speedy commerce has enabled many of 

 the most serious pests of foreign lands to reach and establish them- 

 selves here, till in addition to our own native insects we have also one 

 hundred or "more from abroad, many of them developing destructive 



