June, '17] MORRILL: SOUTHWESTERN COTTON PESTS 313 



this season, located about fifty miles from the insects' present range — 

 the suspension of cotton growing in the district for one season would 

 offer a practical means of complete eradication. The Arizona cotton 

 fields have been closely inspected in the past in order that this and 

 other cotton pests may be promptly detected in the event of their 

 introduction. Proportionally more attention will be given to the new 

 cotton district mentioned which lies between the Salt River Valley and 

 the Santa Catalina Mountains. Even with its proximity to the cotton 

 fields of Arizona, the wild cotton weevil is insignificant in comparison 

 with the pink boll worm as a menace to the cotton industry of the 

 arid Southwest. This latter pest will be mentioned again. The 

 relation of elevation to the future distribution of the weevil in the 

 arid Southwest is an interesting subject for conjectures but not a 

 safe matter to investigate. The insect has been found at elevations 

 from about 2,750 to 7,000 feet but is reported by Coad (3) as more 

 abundant on plants growing at elevations from 3,500 to 5,000 feet. 

 The cotton plantings in the Casa Grande Valley are all below 1,500 

 feet elevation and in the Salt River Valley below 1,300 feet. The 

 discontinuance of cotton growing near Tucson, permanently it is 

 hoped, has removed the most important element of danger, w^hich 

 consisted practically of an intermediate step betw'een the present 

 habitat of the weevil and the important cotton-growing districts of 

 lower elevations. 



HOMOPTERA 



The cotton aphis {Aphis gossypii) is the only representative of 

 the Homoptera which has so far proven injurious to cotton in the arid 

 Southwest. In the season of 1914 this insect, known in the older 

 cotton states as a cotton pest only on account of occasional injury to 

 very young plants, was notably destructive to cotton throughout the 

 greater part of the growing season in the Yuma and Imperial Valleys 

 (15). While no appreciable injury has so far been reported it is 

 interesting to note that adults of a species of the insect family Aleu- 

 rodidse were observed on cotton in the Imperial Valley by Mr. W. D. 

 Pierce in 1913 and a similar observation was made by Mr. Pierce and 

 the writer in the Salt River Valley. The possibility of white flies be- 

 coming injurious to cotton occasionally is shown by a statement from 

 Mr. E, A. McGregor of the U. S. Bureau of Entomology, located in the 

 Imperial Valley in cotton insect investigations, who writes concerning 

 them: "They frequently rise in clouds as one brushes through the 

 rows." In the humid cotton belt we have a record by Ashmead of 

 similar abundance of an Aleyrodid {Aster ochiton abutiloneus) in Missis- 

 sippi with but slight injury. 



