﻿BULiL,ETI]Sr 1374, U. S. DEPARTMENT OF AGRICULTUEE 



plant, Willcocks ® on the other hand reports only 12 per cent of the 

 total eggs deposited on the bolls in Egypt, stating, however, that these 

 data are based on too few records. No doubt the percentage of eggs 

 deposited on different parts of the plant depends to a great extent on 

 the state of growth of the plant and the ratio of bolls to foliage. 



In the summer of 1921 observations were made on plants growing 

 in the field to determine the number of larvae reaching the bolls 

 from eggs deposited on parts of the plant other than the bolls. These 

 tests were begun August 20. Three sets of plants, two plants per 

 set, were selected, and all bolls then on the plants were removed. 

 Thus the bolls as well as the larvae considered in the experiment were 

 produced after the experiment began. After a sufficient number of 

 bolls were set, no more were allowed to form. Every two days all 

 eggs were removed from the bolls on one plant in each set. The 

 other plant served as a check. On September 14 all the bolls were 

 removed from the plants and examined for larvae and exit holes. 



The results of this test are given in Table 1. 



Table 1. — Infestation of green bolls from which all pink bollworm eggs had been 

 removed and of bolls on check plants 





Plant No. 



Number 

 of bolls 



Number 



of eggs 



removed 



Total 

 number 

 of larvae 

 and exit 



holes 



Number of larvae 

 and exit holes 

 per boll- 



Percent- 

 age dif- 





Test 

 plants 



Check 

 plants 



ference 



1 



19 

 15 

 18 

 18 

 11 

 12 



1,326 

 



722 

 



741 

 



104 

 84 



111 



151 

 51 



116 



5.47 





2.3 



2.. . . 



5.60 





3 -_ 



6.17 



26.5 



4 



8.39 







4.64 



52.0 



6 - 



9.67 







Average per boll . . 











158.1 





5.54 



7.80 



28.9 













1 Bolls on check plants not included. 



The most striking points about these results are the great number 

 of eggs removed per boll and the comparatively little reduction (28.9 

 per cent) in infestation brought about thereby. The proportion of 

 eggs deposited in other places than on the bolls is likely to have been 

 higher in the case of these plants than is normal, because of the limit- 

 ing of the number of bolls that grew on them. Considering, however, 

 Loftin's ^ figures (51.7 per cent), first referred to, it would appear 

 that even with only an equal chance for the larvae hatching from 

 eggs on the bolls to enter the bolls, the infestation should be reduced 

 by at least 50 per cent by the removal of all eggs from the bolls. 



From these observations it must be assumed either that the 

 position of the egg on the plant has little to do with the ability of 

 the young larva finally to enter the bolls, or that in this particular 

 experiment, with such a number of eggs present, many of them were 

 so near the bolls that the young larvae hatching from them were in 

 almost as favorable a position as those hatching from eggs on the 



6 F. C. Willcocks. The Insect and related pests of Egypt. Volume I. The insect and related pests 

 injurious to the cotton plant. Part I. The pink bollworm. 335 pp., Ulus. Cairo. 1916. (Sultanic 

 Agr. Soc.) 



' U. C. Loftin, K. B. McKinney, and W. K. Hanson. Op. cit. 



