﻿STUDIES OF THE PINK BOLLWOEM IN MEXICO 



37 



REPRESSION 



CULTURAL CONTROL 



The pink boUworin's habit of pupating in the soil during summer, 

 and of passing the resting period there to some extent, suggests that 

 considerable control may be expected from cultural methods designed 

 to kill the larvae and pupse in the soil. 



IRRIGATION 



In the winter of 1921-22 F. F. Bibby conducted an experiment to 

 show the effect of flooding on resting larvae in the soil. Heavily 

 infested bolls and double seed were placed in a garden under condi- 

 tions as nearly as possible representing those normally found in the 

 field. The material was arranged in plats part of which could be 

 flooded. In these the seed and bolls were buried at several depths, 

 one layer in the first inch of soil, another 3 inches beneath the surface, 

 and a third 6 inches beneath the surface. A fourth layer was placed 

 on the surface of the soil. The latter material floated when water 

 was applied. One plat of each, bolls and seed, was flooded for a 



geriod of 18 days, another for 33 days, and a third for 64 days, 

 lach plat was completely covered with water during this entire time. 

 The flx)ating bolls were kept in water for periods of 18 and 44 days 

 and the seed for 17, 22, 33, and 56 days. 



The data obtained in these experiments are summarized in Table 

 28. In preparing this table the average number of living larvae found 

 in the seed and bolls when the experiment was started was determined. 

 This was considered as 100 per cent and the percentage of living 

 larvae and pupae found in later examinations was calculated on this 

 basis. Forty-seven days after flooding was discontinued on one of 

 the 18-day plats 5 larvae and pupas were found loose in and on the 

 surface.^^ 



Table 28. — Longevity of resting larvae in bolls and seed in flooded and in dry fields 



Approximate date of examination 



Time 

 from be- 

 ginning 

 of treat- 

 ment to 

 examina- 

 tion 



Dayn 



Dec. 26 



Jan. 15 20 



Feb. 4 40 



24 . . fiO 



Mar. 6 "0 



28 90 



Apr. 5 100 



15 HO 



May 24 149 



June 3 159 



Larvae surviving in boUs and seed 



Buried from 1 to 6 inches in soil in field 



In dry 

 plats 



Per cent 

 100 



SO. 9 



18.4 



"i.'s' 



In plat 

 flooded 

 18 days 



Per cent 

 100 



7.6 



4.8 



'i.T 



In plat 

 flooded 

 33 days 



Per cent 

 100 



In plat 

 flooded 

 64 days 



Per cent 

 100 



Floating 

 in water 



Per cent 

 100 

 17.1 

 .2 

 



According to the data gathered in these experiments, the flooding 

 of fields in fall and winter, as (;oinmonly practiced in the Laguna 



"According to Willcocks, Irrigation causes larvsn to leave bolls that are buried and seek the surface of 

 the soil for pupation to a greater extent tiian tlic^y do In dry soil. 



