﻿STUDIES OF THE PINK BOLLWORM IN MEXICO 



63 



The differences here are so shght that the effectiveness of all the 

 poisons must be considered about the same. In the records for 1921 

 (Table 48, plats 2, 4, 6, and 8) the effectiveness of calcium arsenate 

 and that of arsenite of zinc compare in a similar wav. 



ACTION OF THE POISON ON THE PINK BOLLWORM 



In the fall of 1922 experiments were begun to determine the manner 

 in which the apphcation of arsenicals to cotton reduces the pink boll- 

 worm infestation. It was planned to determine by apphcations of 

 dust, in one case to the entire plant except the bolls, and in another 

 to the bolls onty, whether the young larvae are killed while they feed on 

 the fohage or while they attempt to enter the boll. A few plants 

 were selected for each test and young boUs on them labeled, including 

 boUs on separate plants to serve as checks. Applications of dust 

 were made every five days and repeated after rains. An exami- 

 nation of 50 small boUs as a check at the beginning of the experiment 

 showed an average of 0.38 worm per boU. The results of this experi- 

 ment are summarized in Table 51. 



Table 51. — Effect on pink bollworm infestation of the application of calcium 

 arsenate dust on bolls only and on the rest of the plant only 



Part of plant dusted 



Period of treat- 

 ment 



Num- 

 ber of 

 bolls 



Eggs and eggshells 

 on bolls 



Total 



Total 

 egg- 

 shells 



per 

 boll 



Larvae and 

 exit holes 



Total 



Per 

 boll 



larvae 



in 

 bolls 



Entire plant except bolls Sept. 1 to 30 



Check. None 1 



Bolls only Sept. 1 to Oct. 3. 



Check None 



Average, both checks. 



100 

 82 

 50 



58 



227 

 30 

 242 



0.99 

 3.33 



5.12 



209 

 277 

 185 

 256 



2.09 

 3.38 

 3.70 

 4.41 



3.80 



K eduction in infestation was brought about in both cases, but it 

 was more marked where the foliage was dusted than where the bolls 

 only were dusted. It would appear that young larvse were killed 

 both while feeding on the foliage of dusted plants and while entering 

 the bolls. But the most striking point in the results is the great 

 reduction in the number of eggs found on the bolls after dusting. 

 This was found to be the case also in the examination of bolls from 

 plats in the other poison tests. It suggests that the reduction in 

 infestation may not have been brought about at all by killing of the 

 larvae, but by rcpcUing the moths. This point should be closely 

 studied in connection with further dusting experiments. 



SUMMARY 



An average annual loss of from 20 to 25 per cent of the cotton 

 crop has been caused by the pink bollworm in Mexico, since the 

 infestation attained maximum development. There is a reduction 

 in both the quantity of the total crop picked and the quality of the 

 lint and seed marketed. 



