PUSTK BOLLWOEM OF COTTON IN MEXICO. 



51 



Table XXVII is a summary of the experiments with the use of 

 hydrocyanic-acid gas. From these experiments it is seen that it is 

 not practicable to use hydrocyanic-acid gas when the seeds are over 

 4 inches deep. It could not be recommended even when seed is in 

 ordinary bags, for the center of a bag of cotton seed is more than 

 4 inches from the surface of the sack exposed. 



Table XXVII. — Fumigation of cotton seed with hydrocyanic-acid gas. 



Experi- 

 ment 

 No. 



Position of generator. 



Dosage 



per 100 



cubic 



feet. 



Expo- 

 sure. 



Per cent 

 of larvse 

 killed. 



Remarks. 



17 





2-2-4 

 4-4-8 

 2-2-4 

 2-2-4 



4-4-8 



4-4-8 

 2-2-4 

 2-2-4 



Hours. 

 2 

 3 



21 

 2 

 24 



24 



24 

 48 



100.0 

 70.0 

 62.5 

 60.0 

 47.0 



34.0 



10.0 



.6 





24 



do 





18 



do 



Do. 



25 



do 



Do. 



16 



do 





15 





6 inches deep. 



14 



do 



2J inches deep. 



12 





killed 1 foot from floor. 

 Seed in bulk, 5 feet deep. 







POISONING EXPERIMENTS. 



As a possible means of controlling the pink bollworm in the field, 

 poison experiments were conducted in the laboratory with both 

 adults and larvse. Moths readily drink water in captivity when it 

 is sprayed on the leaves or blotting paper in the breeding jars, and 

 it was thought they might be killed by poisoning the drinking water 

 with an arsenical solution. Repeated trials were made by using a 

 solution of calcium arsenate for the moths to drink. The longevity 

 of these moths was the same as that of those in the check, where 

 pure water was used. 



While the laboratory experiments in poisoning the adults were 

 not encouraging, it was thought advisable to try it under field con- 

 ditions. From the habit of the newly hatched larvse of crawling 

 over the plants and bolls before they enter, theoretically it seemed 

 possible that a large number of young larva? might be poisoned. 



Average plats were selected at San Isidera, Tlahualilo, and at the 

 laboratory for poisoning the plants. Weekly applications of pow- 

 dered calcium arsenate were made with hand dusters. These appli- 

 cations were begun about July 15 and continued until the last week 

 in October. The gauges on the machines were opened to their fullest 

 extent and as heavy an application as possible was made each time. 

 (Table XXVIII.) 



