﻿STUDIES OF THE PINK BOLLWORM IN MEXICO 



15 



Bolls of the 1921 crop are still available at the present writing 

 (April, 1923), so Table 13 is incomplete, but the records now indicate 

 a longevity of over 16 months. 



DAMAGE CAUSED BY THE PINK BOLLWORM 



DAMAGE TO IMMATtJRE FORMS 



As pointed out by Loftin,^ the young pink bollworm often enters 

 a square and reaches maturity therein without causing shedding, 

 and the larva may develop to maturity in the bloom without causing 

 abnormal development of the boll. Just what amount of damage 

 the pink bollworm does by feeding on the immature forms on the 

 cotton plant is difficult to determine, owing to the usual heavy natural 

 shed of forms at about the same time that the pink bollworm becomes 

 very numerous. Under conditions prevailing in the Laguna district 

 during 1921 and 1922, the damage done to squares, blooms, and very 

 young bolls early in the season certainly was entirely negligible 

 This point is brought out in Figure 6, in which it will be noted that 

 the rapid fruiting early in the season quickly outstrips the multiplica- 

 tion of the pink bollworm in the blooms. 



Under normal climatic and cultural conditions in this district the 

 fruiting of the cotton is very rapid, once it has well begun. Then a 

 point is reached at which, owing to lack of moisture, all young forms 

 begin to shed off. Later the cotton makes a second growth, which 

 may be very little, or very considerable in case the field receives spring 

 or early summer irrigation. This is illustrated in Figure 6, in which 

 all records after August 21 represent counts in irrigated fields only. 



The results of observations on the relation of shedding to infestation 

 made in a field at Tlahualilo during 1922 are given in Table 14, 

 These observations were discontinued early on account of the appear- 

 ance of the leafworm. The table shows the number of forms on 100 

 plants on the dates indicated, the number of shed forms found under 

 these plants at the same time, and the percentage of these shed 

 forms that were infested. The field in which these observations 

 were made was cultivated on July 18 and irrigated on July 20. On the 

 27th it was again cultivated. Many of the shed forms were therefore 

 either covered up or floated away, which made the figure for shed 

 forms on July 29 unusually low, and not representative of the entire 

 shed since July 14. 



Table 14. — Relation of shedding of immature forms from cotton plants to pink 

 bollworm attack, Tlahualilo, 1922 

 fNumber of forms on and under 100 plants] 





Forms on plants 



Shed forms 



Date 



• 



Bolls 



Squares 



and 

 blooms 



Total 



Percent- 

 age 

 attacked 

 by the 

 pink 

 bollworm 



July 14. ., , 



1,586 

 994 

 947 

 1,008 

 1,038 

 1,162 



712 

 49 

 11 

 127 

 932 

 1,319 



834 



488 



132 



10 



12 



36 



212 



3.5 



29. , 



2.6 



Aug. ft 



4.5 



If, , ,'. 



U 



29. . :L 



33.3 



Sept. 6.. .. ,. ,..w..-,— 



fii.:i 



14.. -..-.. 



09.8 



'——•• ^' 









• U. C. Loftin, K. B. McKinney, end W. K. Hanson. Op. cit. 



