474 



THE GYPSY MOTH. 



The experiments previously recorded show that a consid- 

 erable amount of time is required for the poison used to 

 affect the caterpillars. Those in the earlier molts were 

 killed in a short time, but in the later molts a much smaller 

 per cent, was destroyed, many of the caterpillars transform- 

 ing and producing imagoes. 



In considering these experiments, it should be remem- 

 bered that the insects were in confinement, and obliged to 

 eat the poisoned leaves, while in field work they may some- 

 times find leaves that have not been sprayed, or that have 

 received but little of the poison, and, therefore, the results 

 in some cases might be somewhat different from those 

 obtained in these experiments. 



The remarkable ability of the gypsy moth to resist the 

 action of arsenical poisons is shown in the case of other 

 poisons. Mr. Moulton covered a piece of lettuce leaf with 

 strychnine, and fed it to a caterpillar. In about an hour the 

 caterpillar appeared to be dead, but soon revived and fed 

 again for a short time upon the poisoned leaf, when it rolled 

 over on its back and for several hours remained apparently 

 dead, but afterwards revived again and appeared as well as 

 ever. 



Analyses of Poisoned Larv^. 



The remarkable resistance to the action of arsenical 

 poisons shown by the gypsy moth led us, in the summer 

 of 1894, to institute a series of investigations on the dis- 

 position of arsenic by caterpillars when feeding on poisoned 

 food. For this purpose, gypsy moth caterpillars which 

 had fed for some time upon poisoned leaves without ap- 

 parent injury, and also those which had died as a result 

 of arsenical poisoning, were carefully dissected, the differ- 

 ent organs and tissues being subsequently analyzed at the 

 chemical laboratory of Harvard University. The work was 

 performed, under my direction, by Messrs. Kirkland and 

 Moulton, the former preparing the material and making 

 the dissections, the latter conducting the analyses. All the 

 operations involved were carried on with extreme care, in 

 order to prevent the accidental introduction of any arsenical 

 substance. After each dissection the instruments used were 



