cate whether a field is infested; infested fields are 

 then treated with carefully timed, low doses of the 

 insecticide malathion. 



As a result, the pest has been eradicated from Al- 

 abama, Arizona, California, Florida, Georgia, Kansas, 

 New Mexico, North Carolina, South Carolina, and 

 Virginia. Weevil populations are also declining in the 

 other cotton-producing states: Arkansas, Louisiana, 

 Mississippi, Missouri, Oklahoma, Tennessee, and 

 Texas, as well as in the adjacent Mexican states. The 

 USDA expects the boll weevil to be eradicated from 

 the U.S. by 2009. Nevertheless, the eradication pro- 

 gram has been controversial because of its high cost 

 and, again, its continuing heavy reliance on insecti- 

 cide, which has reportedly triggered outbreaks of oth- 

 er, insecticide-resistant pests. 



Meanwhile, undeterred by impending defeat in the 

 north, the boll weevil remains on the march in South 

 America. It was apparently introduced into the north- 

 ern part of the continent during the late 1940s and, 

 in a mirror image of its U.S. invasion, has moved steadi- 

 ly southward. The insect has now invaded all the ma- 

 jor cotton growing regions ot Brazil and Paraguay, and 

 has entered northern Argentina. Fortunately, this time 

 pest managers have a much greater range of manage- 

 ment options to choose from. Eradication programs 

 in parts of South America are underway. 



Two obvious questions arise from the story of 

 the boll weevil's U.S. invasion: why did the in- 

 sect appear when it did, and where did it come from? 

 The answer to the first question is historical, and rel- 

 atively straightforward. The arrival of the pest in the 

 U.S. can be traced to economic changes wrought by 

 the Civil Wir. The Union's naval blockade of the 

 Confederacy prevented Confederate States from 

 shipping cotton to European textile mills, sending 

 cotton prices skyrocketing worldwide. Mexican 

 farmers, who retained access to European markets, 

 responded by planting more cotton, particularly in 

 northern Mexico. In the years before the Civil War, 

 U.S. cotton farms had been separated from their 

 Mexican counterparts by the wide, cotton-free re- 

 gion of northeast Mexico. But shortly after the war, 

 the northward expansion of Mexican cotton farm- 

 ing had narrowed that region substantially, bringing 

 the cotton fields of the two nations within weevil- 

 flying distance. Increased trade between the block- 



aded South and Mexico may have also helped the 

 weevil cross the border. 



But answering the first question only underscores 

 the lack of an answer to the second: where did the 

 boll weevil originate? Entomologists agreed fi-om the 

 very first that, because the weevil was previously un- 

 known in the U.S. or South America, it must have 

 come from southern Mexico, where it was first col- 

 lected, or perhaps from Central America. They also 

 concurred that the boll weevil, like many other plant- 

 eating insects, restricts its reproduction to a narrow 



The USDA expects the boll weevil to be 

 eradicated from the United States by 2009. 



range of host plants. Hence cotton and its close rela- 

 tives, all members of a group known as the cotton 

 tribe within the family Malvaceae, were the only 

 plants from which the boll weevil could have come. 

 Entomologists and botanists all concluded that the in- 

 sect's origins must be closely linked to the diversity 

 and geographic range of the cotton tribe. 



Those two clues prompted many investigators to 

 search Mexico and Central America for the cradle of 

 the boll weevil. At first, biologists discovered boll 

 weevils only on wild or cultivated cottons — all spe- 

 cies of GossYpiiiiiJ — so they assumed the insect was 

 restricted to that genus. Searches for close relatives of 

 cotton in Mexico and Central America later turned 

 up two more genera from the cotton tribe, Thcspesia 

 and Ciciifiiegosia, that host boll weevils. But hosts from 

 these two genera invariably had few weevils, which 

 occurred only when the plants grew near fields ot 

 cultivated cotton, suggesting that neither genera was 

 likely to have been the boU weevil's ancestral host. 



So cotton remained the prime suspect. Then, in 

 the 1960s, Paul A. Fryxell, a botanist who special- 

 ized in the Malvaceae family at the USDA Cc^tton 

 Laboratory in College Station, Texas, realized that a 

 relatively obscure but diverse genus of small, tropi- 

 cal trees by the name of Hampea had been assigned 

 to the wrong plant family. Other botanists had clas- 

 sifieci Haiiipcd solely on the basis of male specimens, 

 which lack the distinctive tube of fused stamens that 

 surrounds the female flower parts in members of the 



jf Agriculture (USDA) receives 

 i:he boll weevil on U.S. soil. 



1922 Range of boll weevil reaches 

 its maximum extent in the U.S. 



1939 DDI's utility as an insecticide discovered, 

 launching the development of an arsenal 

 of synthetic insecticides. 



1919 Compounds of arsenic first sprayed on 

 cotton fields to combat boll weevil. 



1924 Airplanes first dust cotton with arsenic com- 

 pounds to control boll weevil on a large scale. 



February 2006 NM l'KM IIISIOKN 33 



11 



