20 
BULLETIN 918, U. S. DEPARTMENT OE 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 gossypieUa. 
July 12. 
July 19. 
July 26. 
Aug. 2. 
Aug. 9. 
Aug. 16 
Aug. 23 
From Table IX it is seen that the time of active breeding varies 
considerably, and that hi 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 faU is accumulative. If the offspring from moths 
emerging early in the spring continue breeding throughout the 
