PINK BOLLWORM OF COTTON" IN MEXICO. 43 



and the mortality increased by breaking up and burying the bolls. 

 On the other hand, the bolls float on water and the wind frequently 

 blows them against the borders on one side of the field, where they are 

 piled up several inches or more deep. This concentration keeps some 

 of the bolls out of the water and affords more protection for the bolls 

 in the interior of the pile against heat and cold. If the fields are not 

 irrigated it means they will not be planted the following year and 

 such fields are usually grazed by goats, cows, and burros, which eat 

 many of the bolls. 



Whether or not the results obtained in these experiments during 

 only one winter 5 hold true for what actually takes place in the Laguna 

 it is impossible to say, but they indicate beneficial results from irriga- 

 tion and burying the boils. That a very heavy mortality, probably 

 more than 95 per cent, does take place in the fields is shown by field 

 examinations of the bolls and the very light infestation in the early 

 part of the season. There are such enormous numbers of larvae 

 hibernating in the fields that the crop would be entirely destroyed 

 if the mortality was not very high. 



Willcocks (7) in Egypt left bolls out of doors exposed to the sun on 

 the surface of dry ground and ground that was watered periodically 

 (three waterings). He found a very high mortality during April, 

 May, and June, and all the larvae were dead on June 25. There was 

 a slightly higher mortality among the larvae in the watered bolls and 

 all the larvae were dead on April 8, while some survived in the dry 

 bolls till May 3. His figures "most certainly show that the chance of 

 resting-stage pink bollworms surviving in the bolls fully exposed to the 

 sun on the surface of dry sheraki land in May, June, and July is a re- 

 mote one." He buried another lot of bolls on November 24 in damp 

 soil in boxes. Some of these were kept dry and others wet. Some 

 were stored indoors and others outdoors, though none were in direct 

 sunlight. There was less mortality in the buried bolls than in those 

 left on the surface exposed to the sun, and he says, in speaking of wet 

 conditions, "this does not seem to be materially disadvantageous to 

 the pest. " In all of the buried bolls there was a decided emergence 

 of thelarvae to the top of the soil, which began as soon as the bolls were 

 buried (November 24) and continued intermittently in some cases 

 where the bolls were kept dry till the following November. Water 

 hastened this larval emergence when applied in the fall or the fol- 

 lowing spring, but though the bolls were badly rotted the larvae were 

 still able to remain in them, and spun up in their almost water-tight 

 cocoons during March, April, and May. 



In our experiments in Mexico, larvae survived better in bolls on 

 the top of the ground than when buried and better when left dry 

 than when irrigated. In Mexico the temperature was never as high 



6 These results were substantiated by experiments during the winter of 1919-20. 



