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History and background
The boll weevil, Anthonomus grandis Boheman, is a native of Mexico and Central America. It was first introduced into the United States near Brownsville, Texas, in about 1892.
By 1922, the pest had spread into cotton growing areas of the United States from the eastern two-thirds of Texas and
Oklahoma to the Atlantic Ocean. The boll weevil colonized northern and western portions of Texas during a subsequent range expansion that occurred between 1953 and 1966. By 1981, the insect was well established in parts of California, northwestern Mexico and Arizona.
As early as 1895 the tremendous damage caused by the boll weevill was recognized. Recommendations were made to terminate cotton production in the infested region and to establish and maintain a cotton-free zone along the Rio Grande River bordering Mexico.
In 1903 the Texas Legislature offered a $50,000 cash reward for a practical way to control the boll weevil. In 1904, Sanderson tried to hand-pick infested squares off cotton plants to prevent weevil reproduction.The same year Hunter concluded the boll weevil could not possibly be eradicated. Since that time, numerous methods of control have been tested and reported.
From 1917 until the late 1940s, the most effective method of control was the use of short-season, early maturing cotton varieties and dusting with calcium arsenate. During World War II, DDT and other chlorinated hydrocarbons were developed and made available to control many insect pests, including the boll weevil.
In 1955, scientists reported that boll weevils were becoming resistant to chlorinated hydrocarbons, and within two years resistance was widespread throughout the cotton belt. Concern was growing about the destruction of beneficial insect populations and the widespread occurrence of organochlorines in the environment. Organochlorines were gradually abandoned in favor of organophosphate insecticides. Although the boll weevil has shown resistance to organophospates in Central America, it has yet to develop resistance in the United States, even in the Texas High Plains, where organophosphates have been used in an ongoing diapause program since 1964.
In 1959 researchers discovered that the boll weevil enters diapause during late summer and early fall in ground trash to overcome the absence of host plants and cold winters. In 1964 researchers noted that temperature and photoperiod are key environmental factors controlling the onset of diapause in boll weevils. In 1973 research documented that boll weevil diapause is related to changes in fruiting activity of the cotton plant. The research also showed that diapause occurred in about 20 percent to 50 percent of adult weevils when larval development coincided with decreasing fruiting levels and in 50 percent to 100 percent as true cutout approached.
In 1959 researchers employed insecticide applications late in the season, as the cotton crop approached maturity, to destroy diapausing weevils before they entered hibernation sites. The size of emerging spring populations during the subsequent planting season was greatly reduced.
In 1966 research showed conclusively that the male boll weevil produces a wind-borne sex attractant, or pheromone. In laboratory tests this boll weevil pheromone was isolated by drawing air from caged males through a column of activated charcoal to which female weevils were quickly attracted. Further research showed that the pheromone of the male boll weevil both attracts females and acts as an aggregating attractant for both sexes.
The first synthesis of a boll weevil pheromone compound was reported in 1968. In 1972 improved synthesis produced about one kilogram of the compund for field studies. Several improvements in synthesis have occurred since, including development of the boll weevil pheromone grandlure, now readily available from manufacturers.
As the techniques for formulating grandlure improved, so did the design of boll weevil traps. Among those selected for general use were wing traps coated with Stikem and Plexiglas, oblique funnel traps. In 1971 plywood wing traps painted dark green and metal traps painted yellow were used in a large test in Texas. In the same year, researchers found that weevils were most attracted to daylight fluorescent-yellow traps. Later in the same year, the Leggett trap was developed.
The Leggett trap is a nonsticky trap that uses the behavior patterns of the boll weevil to ensure efficient capture. Traps baited with grandlure were found to be eight times more effective than manual whole-plant examination in detecting very low densities of boll weevil infestation.
In 1980 a trap index system for weevil infestations in West Texas cotton was developed. The sytem was designed to predict the need to treat overwintered weevils, based on catches in the traps before the cotton reached one-third grown-square stage. In the same year, researchers reported that the application of early season insecticide treatments reduced the number of the overwintered boll weevils before they could establish the nucleus of an F1 breeding generation.
Research suggested that the grandlure-baited trap could be used as an effective sampling tool for low-population densities of overwintering boll weevils as they emerge in early spring and search for fruiting cotton. Rummel at al (1980) suggested that 2 percent oviposition-damaged cotton squares following the appearance of one-third grown squares as the level of damage that was predicted to occur between trap index 1.0 and 2.5 on untreated cotton.
About $70 million is spent annually to control the boll weevil, but the pest still causes an estimated $200 million in crop losses each year. In recent years, these figures may have increased by 50 percent. A new control strategy is imperative because cotton cannot be grown profitably unless the weevil is controlled. Yield losses attributed to the boll weevil, the cost of insecticide control, environmental considerations, infestation of secondary insects and insect resistance all have resulted in an aggressive effort to develop a beltwide strategy for controlling the boll weevil in the United States.
Although most growers judiciously apply control measures to boll weevil infested acreage, in almost all such areas 5 percent to 20 percent of the infested acreage may receive inadequate or no control treatments. This uncontrolled acreage harbors populations capable of reinfesting neighboring areas. Models demonstrate that if only 10 percent of a population remains untreated in an infested area, that portion of the population can develop normally and redistribute throughout the surrounding area after only four generations, or less than one growing season. Also, judicious application of control measures cannot protect against reinfestation from neighboring areas the next season. Growers who treat their acreage are faced with a continuing need to apply insecticide to control reinfestations.
In view of the economic and environmental problems posed by the boll weevil and in recognition of the technical advances developed over a period of almost 100 years by hardworking and talented scientists, a cooperative boll weevil eradication experiment was initiated in 1971 in southern Mississippi and in parts of Louisiana and Alabama. This experiment used an integrated control approach including chemical treatment, releases of sterile males, mass trapping and cultural control.
Based on this experiment, a special study committee of the National Cotton Council of America concluded it was technically and operationally feasible to eradicate the boll weevil. The subsequent success of the three-year boll weevil eradication trial, initiated in 1978 on 32,500 acres in North Carolina and Virginia, led to the creation of the southwestern and southeastern boll weevil eradication programs.
The Southwest Boll Weevil Eradication Program was implemented in 1985 to eradicate the boll weevil from about 233,000 acres in western Arizona, southern California and northwest Mexico. In 1988, the program expanded to include 320,000 acres of cotton in central Arizona. Eradication in southern California and western Arizona was completed in 1987, and in 1991 in central Arizona. The Southeast Boll Weevil Eradication Program was designed to eradicate the boll weevil from about 500,000 acres of cotton in the remaining part of North Carolina and in northern South Carolina. This was followed in 1987 with a program in the remainder of South Carolina and in Florida, Georgia and southern Alabama.
The Southeast program also maintained previously eradicated areas in Virginia and the Carolinas as part of a post-eradication plan. A buffer zone on the western edge of the eradication area was also maintained to prevent boll weevil populations from returning to eradicated areas. The Southeast program has since expanded to eastern Mississippi, middle Tennessee and the remainder of Alabama.
The Texas Boll Weevil Eradication Foundation Inc. was established by the Texas Legislature in 1993. The cotton-producer run, nonprofit foundation governs and oversees the implementation of the boll weevil eradication program in Texas. For the 2002 growing season, 11 zones, representing about 6 millions acres of cotton, will be active in the eradication program.
The Southern Rolling Plains zone was the first area to start the program on 220,000 acres in the fall of 1994, and was declared functionally eradicated, the first zone to achieve eradication, in September 2000. The Rolling Plains Central zone was declared functionally eradicated in February 2002.
