﻿64 BULLETIN" 1374, XJ. S. DEPARTMENT OF AGRICULTURE 



The pink bollworm begins its attack on the early squares. From 

 this beginning the numbers of the insect increase with regularity 

 until at the height of the season four or more larvae per boll is a 

 common average and all late bolls are rendered practically valueless. 

 The enormous numbers of larvse that go into hibernation in stored 

 seed and in the bolls and soil in the field insure the presence of 

 sufficient adults to begin the attack the following spring. 



In the summer the larva leaves the boll to pupate. About 80 per 

 cent pupate in the soil, the remainder in and under plant material 

 on the surface of the soil. (Table 3.) The majority of the larvae are 

 found within the first 2 inches of soil (Table 4), and more of them 

 immediately under the plants than between the rows (Table 5). As 

 many as 83 living larvae and pupae have been found in 1 square 

 yard of soil. (Table 6.) Some larvae hibernate in the soil. In some 

 instances over 20 living larvae were found per square yard of soil 

 in the field in winter. (Table 7.) 



The common manner of dispersal is through the carriage of in- 

 fested seed by man. Experiments have shown that isolated plant- 

 ings of cotton even as far as 40 miles from the nearest source of 

 infestation readily became infested where chances of carriage by 

 man were meager but by no means excluded. 



The mortality among newly hatched larvae is great (p. 31). Of 

 the larvae entering the soil for pupation during the summer, 19.7 

 per cent were found to die (p. 32). The attacks of parasites on 

 the pink bollworm in Mexico are spasmodic and as yet have not 

 proved of any importance (p. 36). The mortality of resting larvae 

 in the field during winter and early spring is great, and when fields 

 are flooded in winter hardly any survive. (Table 28.) 



When fields are cleaned in fall and winter and bolls that are shed 

 remain on the soil, many larvae leave these boUs and enter the soil 

 for hibernation. (Table 37.) The survival of larvae during the winter 

 is much greater in bolls on stalks in the field than in boUs on the 

 surface of the soil (Tables 8 and 9), showing plainly the advantage 

 of cutting and burning old stalks. 



The pink bollworm may be killed in cottonseed by heat without 

 injury to the seed. Machines have been made in which the seed 

 is treated either by dry heat or by contact with live steam. By 

 the first method, seed can be disin]Pected by heating to a tempera- 

 ture of 145° F. in 33^ minutes. Bj^ injection of live steam into the 

 seed mass the time of exposure required can be lessened. 



The infestation of green bolls has been reduced as much as 60 per 

 cent (Table 48) by repeated apphcations of arsenicals in the field. 

 This indicates that there is some hope for practical control by this 

 means, but a final conclusion on this point depends on future work. 



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