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 weevil 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 even 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
compound 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 non-sticky 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 system 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.
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