40 PLANT-BUGS INJURIOUS TO COTTON BOLLS. 



This would seem to be the natural result of the insects being fre- 

 quently exposed to direct sunlight. The average daily mean tem- 

 perature during July at Tlahualilo was 81.5° F., and during August 

 at Dallas was 82.8° F., the daily mean for the 2 months averaging 

 82.1° F. There is considerable variation independent of tempera- 

 ture. This is shown by specimens reared from the same egg-batch 

 and kept in the same cage, having in every respect equally favorable 

 opportunities for development. The range in duration of the stages 

 becomes greater with each succeeding instar, which fact is well 

 brought out by Table XVI. 



Cold as a factor in retarding development. — ^At an average daily mean 

 temperature of 69.4° F., the minimum length of the second instar 

 among three specimens of the conchuela was 19 days, the period being 

 from September 26 to October 15. In Table XVI is included a record 

 of 7 days as the duration of this instar in one specimen. This repre- 

 sented the minimum length of the second instar among more than 

 10 specimens of the same brood. The period extended from July 20 

 to July 27, the average daily mean temperature being 77.9° F. A 

 comparison of these two records plainly shows the effect of tem- 

 perature on the duration of nymphal stages. Still greater retarda- 

 tion was exhibited by a lot of 31 fifth-instar nymphs of the conchuela, 

 although the records are not as exact as those given, owing to the 

 fact that the specimens were collected in the field and the entire length 

 of the stage is consequently unknown. The specimens referred to 

 were collected at Barstow, Tex., on October 13, and taken to the 

 laboratory at Dallas, where they were confined in a wire breeding- 

 cage out of doors, and supplied with fresh cotton bolls up to about 

 the middle of November. From among these nymphs adults appeared 

 on the following dates: October 17, 2; October 18, 1; October 19, 2; 

 October 26, 3; November 3, 1. Nymphs were recorded as dead on 

 the following dates: October 10, 5; October 14, 2; October 16, 1; 

 October 26, 1. On December 19, 2 nymphs were still aUve, although 

 feeble and barely able to crawl, owing to lack of food. The average 

 mean temperature at Dallas from October 15 to December 19 was 

 53.7° F., the October average being 62.9° F., November, 57.1° F., 

 and up to December 19, 41° F. 



LENGTH or LIFE WITHOUT FOOD. 



Like the adults, the nymphs of the conchuela, when deprived of 

 food during the summer months, are short-hved. Nymphs in the 

 first instar have been recorded as surviving as long as 5 days without 

 food, which period is the longest ever noted under natural tempera- 

 ture conditions in any instance during the months of July, August, 

 and September. On August 11, 46 nymphs hatched from a batch of 

 eggs and all but 3 of these were dead from starvation on August 14, 



