After 100 Years, Victory Declared Over a Really Bad Bug

After 100 Years, Victory Declared Over a Really Bad Bug
Pink bollworm caterpillar emerging from a cotton boll. Photo Credit: Alex Yelick, University of Arizona

The invasion first came in 1917 in Hearne, Texas. The attack was persistent, relentless, methodical and annually cost tens of millions of dollars and spread to other states. The insidious invader? The pink bollworm.

Earlier this month, U.S. Secretary of Agriculture Sonny Perdue announced that U.S. cotton is free – after more than 100 years – of the devastating pink bollworm. The announcement is a grand celebration for the cadre of scientists, state departments of agriculture and cotton farmers that formed a united battlefront to strategically eradicate a devastating pest through rigorous control and regulatory activities. The victory declaration is significant since the USDA also lifted the domestic quarantine for pink bollworm, relieving restrictions on the domestic and international movement of U.S. cotton.

“Removing pink bollworm regulations eases the movement of cotton to market both domestically and internationally because farmers will have fewer restrictions to deal with, like fumigation requirements,” said Secretary Perdue. “This welcome development comes just as cotton harvest is in full swing across the southern United States. Cotton growers were critical to this success, banding together to carry out a coordinated, multi-state program and shouldering 80 percent of the program’s cost. The coordinated effort demonstrates the value of partnership, investment, and putting our research close to and beside the farmers we serve.”

When the pink bollworm was first detected in Texas, extensive efforts by the Cooperative Extension Service in coordination with individual producers eliminated the infestation in Texas and an infestation found in Louisiana in 1919. In the 1930’s the pest re-invaded the Rio Grande Valley of Texas. By the mid-1950’s, the pest had spread to surrounding states and eventually reached California in 1963.

And one battalion or large body of troops, that successfully battled this bug can be found here in Arizona, one of the “cotton belt” states that grow a high-quality crop. University of Arizona entomologists and Cooperative Extension specialists made key contributions, along with cotton farmers, to this landmark achievement.

Researchers at the UA College of Agriculture and Life Sciences Entomology Department and Cooperative Extension have been studying the pink bollworm, one of the world's most devastating crop pests, for decades. Before its eradication, the invasive insect often completely destroyed cotton fields despite growers' efforts to control them with insecticides.

"The eradication of the pink bollworm is a great achievement that will benefit cotton growers throughout Arizona and the Southwest," said Bruce Tabashnik, who heads the UA Department of Entomology. "This stunning success came from decades of teamwork, with effective collaboration among growers, biotech companies, the Arizona Cotton Research and Protection Council, the USDA, the Arizona Department of Agriculture and University of Arizona extension and research scientists."

The significance of this achievement isn’t lost on Arizona’s cotton farmers who were front and center in fighting this pest. “It’s a great piece of history for the Arizona cotton growers of the state of Arizona,” explained cotton farmer Paco Ollerton of Tierra Verde Farms and recent Arizona Cotton Growers President. “The growers of this state put millions of dollars, sweat and time into eradicating pink bollworm. This was accomplished in an environmentally friendly way, with the use of pheromones, and sterile insect technology, and with very little use of pesticides. The Trans Pecos area of Texas, New Mexico, Arizona, and California have now been declared pink bollworm free.” 

The UA conducted early testing on Bt cotton, which is genetically engineered to control pink bollworm by producing caterpillar-killing proteins from the bacterium Bacillus thuringiensis . The Bt proteins are not toxic to people or wildlife. Bt cotton was a cornerstone of the eradication program.

Since 1996, UA scientists have led a resistance management program that has been essential in suppressing the pink bollworm and stopping it from developing resistance to Bt cotton in Arizona. Tabashnik led the establishment of the "refuge strategy," the primary approach used worldwide to delay the adaptation of insect pests to genetically engineered crops.

U of A research on the pink bollworm determined the genetic basis of its Bt resistance; and developed and implemented sampling methods, bioassays, and DNA screening to assess resistance of field populations of this pest to Bt proteins. UA scientists also analyzed the movement patterns, life cycle, and distribution of pink bollworm on Bt cotton and conventional non-Bt cotton statewide. They devised and applied computer simulation models that incorporated all of the data collected to project the expected outcomes under different management scenarios. These research advances were pivotal in obtaining approval from the EPA in 2006 to conduct the eradication program.

Cotton growers have not had to spray for pink bollworm since 2008. That fact, combined with integrated pest management programs, has saved Arizona cotton growers an estimated $24 to $25 million per year while increasing safety for growers and improving environmental quality.

“We commend all those that were involved in this effort, Ollerton added. “And, we will be diligent in our efforts to monitor and assure that this pest does not get reintroduced.”

The Pink Bollworm, Heavyweight Contender

U of A entomology Extension specialist Peter Ellsworth participated in the testing and led the development of integrated pest management (IPM) programs for cotton. He is the state IPM Coordinator and Director for U of A’s Arizona Pest Management Center in the Department of Entomology. His insights into the monumental task battling this bug are worthy of the history books.

Since the cotton plant is the pink bollworm’s favorite feast, it’s become ground zero in battling a bug that has involved multi-pronged approaches to destroy it. Traditionally, infestations were generally controlled with insecticides. Transgenic Bt cotton that produces one or two pest-killing proteins became a life-saver in the ongoing battle with the pink bollworm, though in parts of India this voracious pest is now resistant to all types of Bt cotton currently available.

Aside from Bt cotton, IPM entails a suite of tactics to suppress this pest, in part, because of the complexities of the pink bollworm lifecycle. Preventing an infestation is carried out the minute a cotton crop is harvested. The field is plowed under as soon as possible to stop the life cycle of the new generation of bollworm. Unharvested bolls can harbor the larvae. Our scientists and farmers even use mating disruption techniques to help destroy the pest.

According to Dr. Ellsworth, the importance of a pest insect can be evaluated in any number of ways. “In terms of economic loss, no question pink bollworm was our worst threat as we entered the 1990s prior to the development of Bt cotton. It has faded in prominence by this metric, ceding to whiteflies and Lygus, but mainly because of the excellent technologies brought forward (e.g., various Bt traits in cotton) and the constant vigilance and stewardship of the growers of this state (e.g., the Plower program, areawide testing and programs of mating disruption, and maintenance and development of the sterile moth production facility / capacity).”

Economic loss can be examined in other ways, too, including a recent economic analysis U of A conducted on Arizona cotton in Ellsworth et al. (2018) and presented to international scientific audiences:

The above chart shows annual, Arizona statewide average yield loss by pest: pink bollworm (pink), Lygus (green), whitefly (yellow) and all other arthropod pests (blue) as a percentage of the total dollars lost to arthropod pests. See the above links for presentations on other measures of economic loss and control costs. Note, eradication efforts began in 2006.

“What I think makes pink bollworm a “heavyweight” contender is its special biology in cotton. Cotton has been plagued by various caterpillar pests since the beginning of time.” Explains Dr. Ellsworth. “Cotton bollworm, tobacco budworm, saltmarsh caterpillar, beet and other armyworms, cabbage and other loopers, and the list goes on. However, one key attribute of these “worms” is that they are surface dwelling caterpillars that for a time travel on the surface of the plant and feed. While each species is damaging in its own right, this provides a vulnerability to human interventions. And, over the last 2 to 3 decades, the industry has brought forward an array of caterpillar-fighting insecticides, all of which depend on this feeding behavior that helps expose worms to these products. While it can be costly, growers have had access to any number of these control chemicals for caterpillar pests.”

“Not so for the pink bollworm, which, as designed by nature, is almost a perfect cotton-infesting machine. Pink bollworm moths fly and arrive in cotton fields by night and lay their eggs very cryptically, often hidden under the calyx of the developing cotton boll, where unfortunately they are protected from any insecticides. But what’s worse is what happens next. Pink bollworm eggs hatch and these tiny, nearly microscopic larvae are pre-programmed to immediately drill through the surface of the boll. In so doing, they are generally unaffected by all these insecticidal innovations of man. Within hours of being “born”, these tiny animals have gained entrance to their home for the next 2–4 weeks, living within their food source, the green, developing cotton boll. It’s there that they find their preferred source of protein, the developing cotton seeds within the cotton boll. With no interest, need, or reason to ever leave the boll, the pink bollworm caterpillar fully develops inside of a single boll, rendering all of these modern insecticides useless in their control.

“Thus, chemical control of pink bollworm, which really targets the flying moths with very toxic insecticides, carries with it the same kinds of odds as you find in Las Vegas, which ever-so-slightly but always favor the bank. And, pink bollworm is the bank. A grower who could control half of the population of pink bollworms invading her field was doing very well indeed. Too bad that the average number of pink bollworms hatching on and attacking a boll were always numerous by late season. Really too bad that only 1 pink bollworm in a boll is all that was needed to completely destroy the boll and worse foul it with invading fungi and boll rot organisms that also could lead to the production of aflatoxin, a dangerous and potent, yet naturally occurring human carcinogen.

“Cultural options like delaying planting and terminating cotton early prior to the fall were very effective control measures for beating the thermal clock that favors the development of all insects in Arizona’s heat, not the least of which was the pink bollworm. However, this “short-season” approach was done at a heavy cost to the grower in a lost opportunity to grow more cotton and higher yields. Margins being what they are, growers could only claim temporary wins in “cultural” battles, but usually lost the economic war and the opportunity to make cotton production profitable.

“In short, conventional controls of pink bollworms were costly, very much less than effective, and fully jeopardizing of the sustainability of this crop in Arizona. For this reason alone, pink bollworm was likely, throughout its history in Arizona, the worst bug to battle in our system.

The damage a pink bollworm can do can go undetected until the boll is fully destroyed since they attack within.

“The development of highly targeted genetically engineered Bt cottons not only reversed those Vegas odds, they made the cotton grower the winner each season (every hand) because it effectively conferred immunity for the cotton plant against the pink bollworm! This coupled with the imagination and innovation of the Arizona cotton growers of this State gave us the opportunity for eradication that many believed would never be possible.”

So why was this declaration so significant? Dr. Ellsworth says, “That’s simple. Because it was so biologically unlikely, so technically difficult and complex, and worst of all, so dependent on broad-scale cooperation of people (and their borders, politics, regulation, science, and industry), which was probably the most difficult thing to achieve. It is a testament to the human capacity to conceive, design, and develop and then to cooperate to overcome a major pest challenge and reach a goal. There are just a few examples of such a broad-scale eradication of a pest species worldwide. In addition to the obvious economic victory that this represents to our growers, this declaration removes a regulatory burden that has existed for decades and cast a shadow on Arizona’s otherwise very high-quality cotton production.”

In 1955, USDA’s Animal and Plant Health Inspection Service (APHIS) established domestic pink bollworm regulations. At the height of the program, 10 states (Arizona, Arkansas, California, Louisiana, New Mexico, Oklahoma, Texas, Nevada, Mississippi, and Missouri) were quarantined for this pest. Many of these infestations were suppressed through cooperative federal, state and industry programs. By 2003, only Arizona, California, New Mexico, and Texas remained under regulation.

Eradication of pink bollworm took years of committed research by USDA’s Agricultural Research Service (ARS), USDA-APHIS, and the University of Arizona. The remarkably successful program included planting transgenic cotton by growers, using insect pheromones to disrupt mating, releasing billions of sterile moths to prevent reproduction and extensive surveys. Many of the research findings became management strategies used by APHIS and cotton growers in their battle against pink bollworm.

The Arizona Cotton Research and Protection Council (ACRPC), a research arm of the Arizona Cotton Growers Association, played a key role in leading the eradication program. Formerly established by statute in 1984, ACRPC serves as a vehicle through which Arizona cotton growers could provide adequate funding for research and applied technology to address industry needs relating to pest control and crop production. ACRPC activities are funded through an annual assessment on each bale of cotton produced in Arizona. As their vision statement on their website says, “The Arizona cotton industry will be provided sustainable programs and technologies to eradicate, control and manage cotton pests.”

After all, most people don’t realize that cotton really falls into the category of a fruit and all sorts of bugs love this unique plant. Without ACRPC’s funding, the ongoing battle of the bugs could not be carried out.

The United States is a world leader in cotton production and trade. According to industry estimates, the U.S. cotton industry accounts for nearly $27 billion in products and services annually, provides hundreds of thousands of jobs across many sectors, and supplies nearly one-third of the raw cotton that is traded globally.

In the meantime, a team of entomologists from the UA and the USDA was recently awarded a USDA grant to continue pink bollworm research in Arizona through 2021. This ongoing work is conducted under secure containment that prevents the pest from escaping into the environment. One of the researchers’ goals is to gain a better understanding of pink bollworm resistance to Bt cotton that has evolved in India and other parts of the world, so if the pest is reintroduced to Arizona, the tools will be in place to defeat it again. According to the Center for Agriculture and Bioscience International, the pink bollworm still occurs in over 100 countries, including parts of Mexico not in the eradication zone.  So, it might be best not to ask if it will be reintroduced to Arizona, but when.

Join Our Family