28 



compounds would not injure foliage, and, with this as a basis, later to 

 test the effects of the poison upon the larva*. The arsenates of the alka- 

 lies, from their extreme solubility, were found to be debarred from use 

 as insecticides, but in the group of alkaline earths the behavior of 

 arsenate of barium was found to present features that would warrant 

 a thorough test of its merits when used against caterpillars. 



Unfortunately, the same legislative policy of delay that hindered an 

 early resumption of our field operations in the spring of the present 

 year also handicapped to a serious extent our experimental work. We 

 were unable to begin insecticide experiments until about June 1, at 

 which time larva? were in the second and third molts and the oppor- 

 tunity for experimentation upon the younger caterpillars had passed. 

 However, it seemed fair to infer from past experiences that poisons 

 effective in destroying the partly grown larva? would be at least 

 equally as effective upon the younger and less hardy caterpillars. 

 Experiments made with barium arsenate upon foliage showed its burn- 

 ing point to be at about the rate of 20 pounds to 150 gallons water. 

 The foliage tests were made upon oak and apple. On hornbeam the 

 burning was more marked, yet not sufficient to cause any great injury. 

 In experimenting with larva? a definite number of the insects was 

 confined by means of thin cloth bags upon foliage sprayed with a known 

 proportion of the insecticide. In the case of larva? in the second, 

 third, and fourth molts feeding upon foliage si>rayed with 3, 4, and 5 

 pounds to 100 gallons water, all were dead in five days. With the 

 fifth-molt larva? from 10 to 20 pounds were necessary to kill all the 

 insects in from six to eight days, showing, as in insecticide experiments 

 of past years, that the resistance to poison increased with the age of 

 the caterpillars. Duplicate experiments, tried after larva? had reached 

 maturity, gave less satisfactory results, on account of the pupation of 

 a considerable part of the insects involved. About 200 larva? were 

 used in these experiments, and where any fed for four or five days upon 

 foliage treated with the poison at the rate indicated death ensued in 

 nearly all cases. 



From results of this season's experimental work it would appear that 

 arsenate of barium is probably the best arsenical compound yet used 

 against the gypsy moth. A limited number of experiments upon the 

 larva? of Hyphantria cunea and Datana ministra showed that 5 pounds 

 to 150 gallons were sufficient to destroy the caterpillars in from four to 

 eight days. We simply wish to bring this poison to the notice of the 

 association, so that it may be tested further by those who may so 

 desire, and thus its actual merits will be demonstrated. We feel that 

 more experimentation is absolutely necessary, and particularly the 

 extended use of the poison on a large scale, in actual field operations, 

 before we can get at its true value. 



Mr. F. J. Smith, chemist to the committee, informs me that this 

 poison may be prepared by a process similar to that employed in the 



