26 BULLETIN 918, U. S. DEPARTMENT OF AGRICULTURE. 



The data in the foregoing table were compiled from records kept 

 of weekly examinations made of 100 boll (green) samples taken from 

 different plantations in the Laguna district. The bolls in each sample 

 were taken by walking through the same fields each week and pick- 

 ing the bolls at random. 



ESTIMATE OF DAMAGE TO LAGUNA CROP, 1919. 



In making an estimate of the damage caused by P. gossypiella to 

 the cotton crop of the Laguna for 1919, it was thought best to select 

 certain average fields on average plantations and to keep these 

 particular fields under close surveillance during the entire year. 



Through the courtesy of Don Carlos Gonzales y Farino, of Torreon 

 and of the Tlahualilo Company, Tlahualilo, Durango, certain fields 

 upon their properties were selected. These fields were chosen with 

 the utmost care in order to obtain as nearly as possible an average 

 of all conditions of the Laguna, with respect to factors controlling 

 the amount of damage caused by P. gossypiella. Other fields in dif- 

 ferent parts of the Laguna were examined as often as time would 

 permit for comparison with these fields. Each of these fields was 

 visited regularly (as far as conditions would permit) once a week, 

 and samples of 100 green bolls taken, so that the rate of increase of 

 infestation might be ascertained. 



Samples of seed cotton were also taken at the beginning of each 

 pick from each of the experimental fields, to determine the damage 

 caused by the pink bollworm in the different harvesting periods. 

 These samples were ginned in a sample gin separately, accurate 

 weights being kept of the quantity of lint and seed. A sample of lint 

 from each field sample was taken for classification by the Bureau of 

 Markets, United States Department of Agriculture, to determine 

 the discolorations, grades, and spinning qualities of the lint. 



A 2-pound sample of seed was taken from each field sample for 

 chemical analysis to determine quality and quantity of oil. 



DAMAGE TO SQUARES AND BLOOMS. 



The pink boll worms enter the squares just after hatching from 

 the eggs, and continue feeding until they complete the larval stage, 

 notwithstanding the fact that the squares may bloom in the mean- 

 time. Larvas of all stages have been found in the squares, but 

 generally speaking only full-grown larvae have been observed in the 

 blooms. To ascertain to what extent this floral feeding habit tended 

 to cause damage the following experiment was carried on. 



Tags were placed on 343 normal blooms and on 343 infested blooms 

 during June and July. Table XII shows the results. 



