138 THE GYPSY MOTH. 



latter would be more quickly dissolved in the digestive 

 fluids of the caterpillars. This subject, however, needs 

 more scientific investigation, as the experiments made were 

 too limited in scope to allow any conclusions to be based 

 on the results. As it was found later that neither brand 

 of Paris green gave as satisfactory results in the field as 

 had been obtained in-doors, and as the use of this arsenite 

 was finally given up, the subject of the comparative efficiency 

 of the pulverized and the ordinary Paris green was not 

 further investigated. 



The results obtained by in-door experiments with the pul- 

 verized Paris green led to experiments on a larger scale in 

 the field and accordingly a ton of this poison was purchased. 

 Early in May spraying in the field was begun (see page 55). 

 Most of the sprayers were supplied with the fine Paris green, 

 which, though not proving as efficacious as in the laboratory, 

 nevertheless killed many of the smaller caterpillars. As the 

 spraying continued it was observed that a considerable pro- 

 portion of the caterpillars of middle age were also destroyed. 

 Sometimes, though rarely, persistent spraying appeared to 

 destroy most of the larger caterpillars. By this time it had 

 been determined by experiments in the laboratory that Paris 

 green would not kill all the larger larvae ; yet as it had 

 given better results than any other insecticide, it was thought 

 best to continue its use at varying proportions in the field, 

 and the poison was used at a strength of from one to four 

 pounds to one hundred and fifty gallons of water. As a 

 rule the spraying did not seriously burn the foliage when a 

 solution was used consisting of one pound of Paris green to 

 one hundred and fifty gallons of water; but with larger 

 proportions of poison the foliage was considerably burned. 

 The injury developed so rapidly that within a short time the 

 leaves were all killed and the surviving larvae were obliged to 

 go elsewhere to feed. Therefore, a strong Paris green mixt- 

 ure had little better effect than a weak one. Lime was 

 then used with the Paris green with a view of neutralizing 

 the burning but considerable injury to the foliage still con- 

 tinued. 



Though even when three or four pounds of the Paris green 

 were used to a tank of water, many of the larger feeding 



