20 



BULLETIN 918, U. S. DEPARTMENT OF AGRICULTURE. 



cotton plants during March and April, 1918, were unsuccessful. 

 The first eggs were laid in the breeding jars on May 5, and the first 

 larva (one of the third instar) was found in cotton in the field on 

 May 15, 1918. The first eggs were deposited on April 9, 1919, and 

 the first larva found in the field on April 28. The general infestation 

 in the fields, however, did not begin till later in 1919 than in 1918. 



In general, it may be said that breeding commences in the spring 

 as soon as the squares begin to mature and by the time the first 

 blossoms appear a few larvae are present. The infestation is 

 extremely light at this season and only by careful search will any 

 larvae be found. As a rule the bolls are not attacked till they are 

 from one-half to three-fourths grown, though occasionally a larva 

 works down from the blossom to the newly set boll. It is usually 

 about the middle to latter part of July before bolls on plant cotton 

 are sufficiently mature to be attractive to the larvae. From this 

 date onward the infestation rapidly increases, and in about 10 weeks' 

 time practically every green boll is infested. The cool nights of 

 October and November check the development somewhat, but 

 breeding continues until frost destroys the food plants. 



Table IX shows the weekly increase in the percentage of green 

 bolls infested during the 10 weeks during which breeding is most 

 active. It is computed from weekly examinations of samples of 

 green bolls collected on different plantations, an average number of 

 350 in 1918 and 1,100 in 1919 being used. 



Table IX. — The -weekly increase in the percentage of green bolls infested with Pectino- 



phora gossypiella. 



Week ending- 



July 12. 

 July 19. 

 July 26. 

 Aug. 2. 

 Aug. 9. 

 Aug. 16 

 Aug. 23 



Percentage of green 

 bolls infested. 



1918. 



1919. 



1.1 

 7.0 

 13.6 

 20.0 

 21.0 

 42.0 

 65.8 











4.3 

 5.0 

 10.8 



Week ending- 



Aug. 30. 

 Sept. 6.. 

 Sept. 13. 

 Sept. 20. 

 Sept. 27. 

 Oct. 4... 

 Oct. 11.. 



Percentage of green 

 bolls infested. 



79.2 

 93.0 

 97.3 



20.8 

 29.0 

 41.0 

 45.0 

 63.0 

 83.3 

 100.0 



From Table IX it is seen that the time of active breeding varies 

 considerably, and that in 1919 it was a month later than in 1918. 

 This depends largely upon the development of the cotton. The same 

 climatic conditions which retard the growth of the cotton also affect 

 the activity of the species, and the relative development of the two 

 is about the same from year to year. It is also clearly shown that 

 there are no distinct broods or generations and that the heavy 

 infestation in the fall is accumulative. If the offspring from moths 

 emerging early in the spring continue breeding throughout the 



