﻿32 



BULLETIN 1374, U. S. DEPARTMENT OF AGKICULTUEE 



A higher mortality among the larvse and pupse between the rows 

 than among those immediately under the rows is noted. 



Table 26 shows the relative mortality among pink boUworms at 

 different depths in the soil. The mortality is greatest in the first 

 2 inches of soil, decreasing with the depth. An average for all depths 

 in this table gives 19.7 per cent mortality. 



Table 26. — Mortality of the pink bollworm at different depths in 



the soil 





Pirst 2 inches 



Second 2 inches 



Third 2 inches 



Date of examination (1921) 



Larva3 and 

 pup 86 



Pupal 



cases 



Larvas and 

 pupae 



Pupal 

 cases 



Larvae and 

 pupae 



Pupal 





Living 



Dead 



Living 



Dead 



Living 



Dead 





July 21 . - 



5 

 70 



3 



31 

 11 



2 



4 



8 

 18 

 17 

 17 

 3 

 

 2 







13 



45 



2 



6 



39 



9 







16 







5 







2 



25 



3 



No examinatioTi 





Aug. 4 



2 

 2 

 8 

 1 

 

 



1 

 

 2 

 2 

 

 







19 - 



5 3 



15 



Sept. 6 



12 



5 







25. -_ 



1 



Oct. ]8 





 1 





 



2 

 3 







29 . -. - - .- 











Total 



126 



fi."; 



114 



34 13 



■^^ 



13 



5 



16 













Total, all stages _.. 



305 



82 



34 









Percentage dead 



21.3 



_ _ _ 15.8 



14.7 















MORTALITY OF LARV^ IN THE RESTING STAGE 



The pink bollworm larva passes its resting period in or about seed 

 or seed cotton in gins and warehouses, in the bolls in the field, and 

 in the soil. As the activity of the insect lessens in the fall, an increas- 

 ing percentage of the larvae spin up in the boll and assume the resting 

 stage. This shows their normal preference for hibernating quarters. 

 Larvse that hibernate in the soil evidently do so because the boll in 

 which they mature does not offer suitable quarters. It may either 

 still be green when the larva is ready to make its cocoon, or it may 

 have fallen to the ground, where the sun's heat becomes so excessive 

 that the larva enters the soil. 



MORTALITY OF LAEV^ IN BOLLS AND SEED IN STORAGE 



One hundred bolls collected from standing stalks in the field on 

 March 9, 1921, showed a total of 109 living larvse and 15 dead ones. 

 Bolls in storage furnish equally as good quarters for the resting 

 larvse. Of the larvse in bolls that had been collected from the fields 

 in the middle of November, 1921, and stored, 10 per cent were dead 

 in March, 1922, and in others that were collected early in December, 

 1922, 7 per cent were dead on February 7, 1923. Usually the larvse 

 in seed or bolls in storage are attacked by mites, and mortality from 

 this cause rises very rapidly in the spring. 



Tables 12 and 13 give records of larvse in stored seed and bolls of 

 the 1920 and 1921 crops. According to these data, the larvse survive 

 longer in bolls than in the seed. As all this material was stored 

 under the same conditions in the laboratory, the most likely explana- 

 tion for the difference is that larvse in loose seed are more accessible 

 to mites than those in the bolls. The more rapid decrease of the 



