12 



BULLETIN 358, U. S. DEPARTMENT OF AGRICULTURE. 



Cotton terminals. — Seventy-five pairs of weevils were fed on cotton 

 terminals during the season and observations were made on a total of 

 1,920 weevil days. Feeding was observed on 1 ; 226 weevil days. 

 On 616 days the weevils fed on the stem alone, or 50.2 per cent of all 

 feeding was on this part. On 602 days, or 49.1 per cent of the feeding 

 days, the feeding was on both the stem and bud, while the bud alone 

 was attacked on only 8 days, or 0.7 per cent of the feeding days. 



The preference of the weevil for the stem in these two series was 

 quite marked. This may be due to the mechanical stimulus presented 

 by the shape of the stem which will allow punctures more or less like 

 those made in the squares and bolls. 



Table V. — Relative proportions of the sexes of boll weevils. Observations of 1915. 



Variety and description of material. 



Male. 



Female. 



Number. 



Per cent. 



Number. 



Percent. 



Grandis: 



439 

 1,591 



55.00 

 51.59 



360 

 1,493 



45.00 





48.41 







Total grandis 



2,030 



52.28 



1,853 



47.72 







Thurberiae. 



71 

 4 



55.98 

 40.00 



56 

 6 



44.02 





60.00 









75 



54.74 



62 



45.26 







Hybrids: 



Male thurberiae and female grandis 



52 

 50 



50.49 

 44.25 



51 

 63 



49.51 



Male grandis and female th arberiae 



55.75 







Total hybrids 



102 



47.22 



114 



52.78 







Total and average of all weevils 



2, 207 



52.10 



2,029 



47.90 







SEX OF ADULTS. 



A considerable number of the weevils handled during the season 

 were sexed, and Table V shows the ratio of the sexes. 



Of the hibernated grandis material, 439 were males and 360 were 

 females, or 55 per cent males and 45 per cent females. Of the thur- 

 beriae weevils extracted from Thurberia bolls, 54.74 per cent were 

 males and 45.26 per cent were females. Of the 214 sexed hybrid 

 weevils bred during the season 47.22 per cent were males and 52.78 

 per cent were females. These last figures are in accordance with the 

 observations in 1913 that there was a larger percentage of females in 

 variety thurberiae and the hybrids than in the variety grandis. 



PERIOD FROM EMERGENCE TO OPPOSITION. 



In the series of typical grandis females the period from emergence 

 to oviposit ion when fed on squares varied from 2 to 16 days with an 

 average of 6.6 days. Fourteen females emerging in late June 

 averaged 5.9 days from emergence to oviposition and 5 females 

 emerging in late July and early August averaged 8.8 days from 

 emergence to oviposition. Thus it is shown that temperature has a 



