March of the weevils: how a Mexican beetle launched a hundred-year attack on United States cotton

Natural History, Feb, 2006 by Robert W. Jones

More than a hundred years ago, a curious-looking insect appeared in the United States that would dramatically transform the economy and landscape of the cotton-dependent South. The first report from the front lines of the unfolding U.S. invasion came in October 1894. That's when a small vial of insects arrived at the headquarters of the U.S. Department of Agriculture (USDA) in Washington, D.C., sent by a pharmacist named Charles W. DeRyee from Corpus Christi, Texas. In those days, farmers made insecticides from chemical ingredients they bought at a local drugstore. When a new and perplexing pest had appeared on cotton farms near Corpus Christi, local farmers had naturally turned to DeRyee for help. The pharmacist, in turn, sent the offending insects off to the USDA, accompanied by a troubling note that described damage to the fruits growing at the top of the area's cotton plants:

The "Top" crop of cotton of this section has been very much damaged and in some cases almost entirely destroyed by a peculiar weevil or bug which by some means destroys the squares and small bolls. Our farmers can combat the cotton worm but are at a loss to know what to do to overcome this pest.

An insect taxonomist at the USDA, Eugene A. Schwarz, identified the "peculiar weevil" as Anthonomus grandis, a member of the Curculionidae, or "snout beetle" family, so-named for its members' unique, elongated snouts. When Schwarz and, independently, C.H. Tyler Townsend, an entomologist from New Mexico College of Agriculture and Mechanical Arts (now New Mexico State University) in Las Cruces, went to Texas to observe the weevil and the damage it caused, they quickly realized the animal's destructive power and alerted the world to the threat it posed to cotton production.

What those investigators saw is characteristic weevil activity. Adults pierce the flower buds, or "squares," with their long snouts and eat the pollen within. They also puncture the immature fruits, or "bolls," to consume the developing cotton fiber. More important, the females bore holes deep into both squares and bolls to deposit their eggs. After hatching, the larvae consume the innards of the plant's reproductive structures. Damaged squares are then severed from the plant, never to become boils. And most of the damaged bolls fail to produce their trademark fluffy fibers. Anthonomus grandis, a modest, quarter-inch-long insect, soon became known as the notorious cotton boll weevil.

The appearance of a field heavily infested by weevils is a depressing sight to any cotton farmer, but it must have been devastating to those who first witnessed the destruction. When weevils are finished with a cotton plant, the plant retains its lush, green foliage, but it has none of its distinctive large, white and pale-pink flowers or fiber-producing fruits. Yellowed, weevil-infested buds are scattered over the ground like confetti.

Yet even for the cotton farmers who first surveyed such depredations, it would have been hard to imagine the sweeping trajectory of the weevil's invasion. From their fields it marched across the South, leaving massive agricultural and economic disruption in its wake. Even today the cost of the pest in crop losses and control measures in the U.S. is estimated at around $150 million a year, and the cumulative costs of the invasion exceed $22 billion. Fortunately for U.S. cotton growers, the war on the boll weevil, begun more than a century ago, is finally being won. The insect has been eradicated from tell states, and it is in retreat in seven more. Unfortunately, the principal weapons in this war have been chemical insecticides, some of which, especially initially, have left toxic residues that are likely to persist for many years.

A second unfortunate reality is that much of the war against the boll weevil had to be fought without knowing the biological history of the enemy--where it came from or why. The mystery can be traced to an obscure taxonomic error. Correcting that error eventually led to a vastly improved understanding of the weevil's natural history, but that understanding came too late to have much impact on the U.S. eradication effort. In fact, the success of the eradication effort led to cuts in spending on research into alternate methods of weevil control. Does that mean the enhanced knowledge is of no more than academic interest? Quite the contrary. The boll weevil may be in retreat in the U.S. but it remains a key cotton pest in Mexico and Central America. In those countries the presence of the weevil's wild host plants may make it futile to apply U.S. eradication methods. More worrisome is that the insect has opened a second front in South America. That invasion continues mounting to this day. Understanding the boll weevil's origins, its natural enemies, and the defenses that relatives of cotton might have evolved against its ancestors may one day help reduce the need for pesticides to control it.

As early as 1802, some thirty-two years before Charles DeKyee's alert, the boll weevil had already been reported destroying cotton plants in what were then wild and isolated regions of Mexico's northern states. That earlier report caused little stir in the U.S. By 1900, however, the weevil was well entrenched in southern Texas and plainly displaying its destructive potential. A growing alarm was spreading among cotton growers throughout the South.