APPENDIX. xxxvii 



from the fact that the caterpillars seem unusually resistant to the 

 action of arsenic in doses fatal to most of the insects known to us. 



There is one criticism to be made on all the above experiments : 

 they are on too small a scale to render the results altogether convinc- 

 ing and they are made in the wrong place at Amherst rather than at 

 Maiden, Lynn or elsewhere in the infested region. The extreme 

 caution necessary to prevent the escape of specimens of the larvae 

 prevents the practice of certain lines of out-door work, the results of 

 which would supplement the in-door or laboratory experiments. 



I would therefore suggest that the experiments now carried on 

 at Amherst be duplicated or transferred to some point within the 

 infested district where material is more abundant, and where there 

 is no danger of introducing the insect into new localities. 



These experiments must of course be made by a trained ento- 

 mologist, or by a competent man under detailed instructions. By 

 all odds the most satisfactory plan would be to have you carry on 

 the experiments yourself, for they would then command universal 

 acceptance and would be generally regarded as conclusive. 



The result of the insecticide experiments thus far is so unusual 

 that I would recommend a further series of experiments to deter- 

 mine exactly what becomes of the arsenic eaten by the insects ; 

 whether it is absorbed or whether it is excreted, and how much 

 arsenic an insect will contain when its intestinal canal is filled with 

 poisoned food and excreta therefrom. This could be done by 

 feeding larvae on leaves sprayed with a maximum amount borne 

 by the foliage for say three or four days, and then substituting 

 fresh food free from poison. A chemical test should be made 

 thereafter every day or every day or two, to ascertain the presence 

 or absence of arsenic in the larvae. Microscopic examinations of 

 the digestive tract of poisoned larvae should also be made, and 

 should be compared with that of healthy larvae, to ascertain 

 whether any lesion were caused that might result in a degenerated 

 adult. The excreta of larvae fed upon poisoned food should also 

 be analyzed to determine the amount disposed of in this way. 



This is of course suggestive merely ; but in my opinion the 

 present occasion is an unusually good one to gather a mass of 

 facts whose importance to economic entomology it would be dif- 

 ficult to estimate. 



If I had reason to speak in approbation of the line of experi- 

 ments laid out by yourself at Amherst, I found very much more 

 to admire in the infested district, in the actual field work under 

 the direction of Mr. Forbush. The mere organization of the force 

 and the plan of the work is excellent ; as to the results of the 

 methods adopted, the fact that in the entire infested district 



