THE BOLL WEEVIL LOFTIN 279 



4, August 1934). Thurberia occurs in the United States only in 

 the mountains of southern Arizona and New Mexico, where it is 

 too hot and dry for the boll weevil to become established. However, 

 a variety of the boll weevil more resistant to arid conditions, known 

 as the Thurberia weevil {Anthonomus grandis thurberiae Pierce), is 

 well established in Thurberia in central Mexico and Arizona and 

 in cotton on the west coast of Mexico. The Thurberia weevil prob- 

 ably reached the United States long before the boll weevil, but no 

 cotton was grown in the area and it was of no importance at the 

 time. Cotton production extended westward to escape boll-weevil 

 damage, and the Thurberia weevil transferred to cotton when planted 

 near its habitat. The first Thurberia weevils were found in fields 

 near Tucson, Ariz., in 1920. It differs from the boll weevil in hav- 

 ing only one generation a year on Thurberia and in the adults' pass- 

 ing the winter only within the dry seed pods of Thurberia or bolls 

 of cotton. Although the Thurberia weevil readily attacks cotton 

 and develops two or more generations a year, it does not become 

 abundant enough to cause serious damage to cotton grown under 

 irrigation. The habit of the adults' remaining within the pupal 

 cells until emergence is stimulated by moisture has become so thor- 

 oughly fixed that it was not changed by experimentally maintaining 

 Thurberia weevil on cotton for 10 years, and at the end of the ex- 

 periment an irrigation of the field for planting cotton caused all 

 the adults to emerge and perish before squares became available for 

 food. Carefully controlled biological tests have shown that the 

 Thurberia weevil will interbreed with the boll weevil, and it is 

 feared that if it should become established where the boll weevil 

 occurs, a more vigorous hybrid strain of cotton-feeding weevil might 

 result. The natural climatic barriers have prevented the boll weevil 

 from moving westward and a quarantine requiring treatment of cot- 

 ton moved from the Thurberia weevil area has maintained the gap 

 between the two insects. 



CULTURAL METHODS 



Changes in cultural methods that hasten early maturity of the 

 crop were developed and adapted rapidly after establishment of 

 the boll weevil in south Texas. One of the recommendations of the 

 first entomologist to investigate the boll weevil — the early destruc- 

 tion of the cotton stalks — has been proved by later research to be 

 biologically sound. Early fall destruction of the stalks removes the 

 food from weevils, stops the late season breeding and build-up in 

 numbers, and causes the adults already present to enter hibernation 

 in a semistarved condition that increases the winter mortality. That 

 the earlier the stalks are cut the more effective this method of control 



