INSECTICIDES. 485 



No. 6. - — May 22, 1894. Ten caterpillars, before the 

 first molt, were placed in a dish and sprayed with sulpho- 

 naphthol, and then put on a fresh leaf. Six died on the 

 fourth, one on the fifth, one on the sixth and two on the 

 seventh day. Tlie strength of the sulpho-naphthol used in 

 this trial was in the proportion of 1 part to 50 parts of 

 water. 



Cyanides. 



Studies on the anatomy of the caterpillars, made in 1894, 

 by Mr. Kirkland, showed that the contents of the alimentary 

 canal were strongly alkaline. This suggested the idea that 

 some compound might be prepared which would be inert 

 under ordinary circumstances, but when taken into the diges- 

 tive system of the insect would decompose in the alkaline 

 medium and form a deadly poison. Following out this idea, 

 Mr. Moulton prepared a number of the compounds of cyanic 

 acid, which were experimented with during the summer of 

 1895. The substances tried were the cyanides of lead, 

 copper, antimony, zinc and mercury. The last-mentioned 

 compound burned the foliage badly, hence but few experi- 

 ments were made with it. Of the other compounds, cyanide 

 of copper was the only one which gave eifective results, and 

 these were not as satisfiictory as can be obtained from the 

 use of the same weight of Paris green. The other cyanides 

 are practically valueless, since caterpillars were fed through- 

 out their entire life on foliage treated with large proportions 

 of these three compounds, without sufiering injurious effects. 



Contact Insecticides. 

 "Whale-oil soap, several proprietary soap powders, soft 

 soap and kerosene emulsion were experimented with during 

 the summer of 1891, for the purpose of finding a cheap con- 

 tact insecticide, for use where the caterpillars cluster in 

 masses on trees, fences, etc. All of these insecticides were 

 found to be fairly effective. 



Food Selection. 

 The following experiments were conducted, both at the 

 storehouse and in the field, by Mr. Kirkland, during 



