New study shows "strong evidence" of Bt resistance
NOTE: A new study led by a pro-GM researcher shows "strong evidence" of Bt resistance after carefully analyzing 41 reports from 5 continents. Among other things the resewarchers discoved through a Freedom of Inofrmation request to the EPA that Herculex GM corn had to be pulled from Puerto Rico after the discovery of widespread insect resistance. The resistance was so bad that Dow and Pioneer had to withdraw their GM (Bt) seed from the market and advise growers to spray pesticides instead.
EXTRACT: Tabashnik said the rebuttal of his earlier study on cotton was a letter, not a study, and was signed by seven researchers with financial ties to Monsanto. "There was no criticism in that letter that had a sound, scientific basis," he said.
UA researcher says crop pests abroad resistant to controls
By Tom Beal
Arizona Daily Star, 12.22.2009
A UA researcher says pests that destroy corn and cotton have developed resistance to the most effective and benign method to kill them.
Bruce Tabashnik, University of Arizona research entomologist, said resistance does not pose an immediate threat to the vast acreages of Bt corn and cotton grown with genetically introduced Bt toxins, but argues for continued monitoring.
Tabashnik's study, published this month in the Journal of Economic Entomology, analyzed 41 reports from five continents. It uncovered "strong evidence" of naturally evolved resistance in an obscure journal, an unpublished government report and multiple studies that he said failed to reach the obvious conclusions their data supported.
Officials for Monsanto, which dominates development of the world's genetically modified crops, concede resistance to Bt developed in isolated fields in South Africa and Puerto Rico, but dispute Tabashnik's other claims.
Scientists have long expected corn and cotton pests to develop resistance to Bacillus thuringiensis, or Bt.
Since their introduction as transgenic seed products in 1996, various Bt products have proved effective in reducing damage to cotton bolls and corn crops and have let growers reduce the amount of pesticides sprayed on crops worldwide.
Bt is a naturally occurring soil bacteria that is used by organic farmers to ward off pests. The U.S. Department of Agriculture says "use of Bt cotton reached 65 percent of planted cotton acreage in 2009 and Bt corn use grew from about 1 percent of corn acreage in 1996 to 63 percent in 2009."
Worldwide, about 25 percent of corn and cotton are grown from Bt seed, said Tabashnik, and the incidence of resistance is very small.
"This is a success story and should be portrayed as such," said Margaret Mellon, director of the food and environment program at the Union of Concerned Scientists.
"Bt is a splendid pesticide. It is notable for the fact that it goes after pest insects without having effects on mammals or other organisms," said Mellon. "This is the kind of pesticide we want to work as long as possible."
Keeping it working requires honest discussion of problems that arise, Mellon said.
She said Tabashnik's work in this and other studies is important for growers, seed companies and consumers who all have an interest in preventing development of Bt-resistant insects.
Reports of resistance would have been a "tragedy" a few years back, said Fred Gould, an expert on insect ecology and evolution at North Carolina State University.
"But now the (seed) companies have the ability to see this and the technology has moved ahead and they should be able to remedy this issue," said Gould.
Gould said Tabashnik's research illustrates the need to stick to practices recommended by scientists and ordered by the EPA that require a potent dose of Bt and "refuge" fields where non-Bt crops can house non-resistant insects to dilute the population of resistant insects.
The studies unearthed and analyzed by Tabashnik show that resistance can evolve more rapidly when recommendations are not followed, Gould said.
In one 2006 case in Puerto Rico, the paper says, the EPA concluded that a moth species, whose larva is known as fall armyworm (S. frugiperda), developed resistance to Bt corn crops that expressed a toxin known as Cry1f.
Dow AgroSciences and Pioneer Hi-Bred International reported the incident to the EPA, withdrew the seed from the market and advised growers to spray pesticides.
The incident was not reported in any peer-reviewed journal, Tabashnik said. He got the data with a Freedom of Information Act request to the EPA.
A similar lack of safeguards led to resistance to a Monsanto Bt corn in South Africa by a stem-borer known as B. fusca in the 2005-06 and 2007-08 growing seasons.
That evidence was reported in the South African Journal of Plant and Soil. The journal is not available through online scientific sites; Tabashnik, working with a grant from the U.S. Department of Agriculture, went to South Africa and gathered the data. It's author, J.B.J. Van Rensburg, became a co-author of the report, along with Yves CarriÃ¨re, also of the UA's Department of Entomology.
A more widely known reinfestation of Bt cotton crops by a bollworm in the Southeastern United States between 1992 and 2006 was reported in at least five scientific publications, said Tabashnik, but researchers never used the data to draw the conclusion that the bollworm in question, Helicoverpa zea, evolved resistance to Cry1Ac, the toxin in a Monsanto product called Bollgard.
A Monsanto spokesman disputed Tabashnik's characterization of the problem in the Southeast United States, but conceded that the South African and Puerto Rican incidents were evidence of field-developed resistance.
Those incidents were limited to small areas where effective management practices were not followed, said Timothy Dennehy, lead researcher for insect resistance management in cotton for Monsanto.
Dennehy, a former colleague of Tabashnik at UA, said earlier claims of field resistance to Bollgard in the Southeast were rebutted by "the entomological community in the South." Dennehy said a second generation of Bollgard with 2 Bt toxins is now available to growers in the Southeast.
"Why would you be trying to find fault with something that is by no means a clear and present danger?" he asked.
Tabashnik said the rebuttal of his earlier study on cotton was a letter, not a study, and was signed by seven researchers with financial ties to Monsanto.
"There was no criticism in that letter that had a sound, scientific basis," he said.
Some of Tabashnik's own research is underwritten by Monsanto. His department at the UA monitors resistance to the Bt cotton program in Arizona. The principal cotton pest in the Southwest ”” pink bollworm ”” is very susceptible to Bollgard and has shown no signs of evolving resistance. It is an "unqualified success," Tabashnik said.
Mellon, of the Union of Concerned Scientists, said a series of "lucky breaks" kept resistance to Bt from developing worldwide.
Bt resistance is a recessive trait in most pests, meaning two resistant pests would have to mate to produce resistant offspring.
"That's lucky for the world," she said, "but this is no time to slack off and to foolishly think we've beaten the bugs."
Tabashnik is a fan of Bt crops, but considers himself "an honest broker of information" in the politically charged world of genetically modified crops.
He wants genetic modification to be used wisely, in scientifically based programs that prevent, or at least ward off, development of resistance.
The overwhelming success of the Bt crops has made growers a bit complacent, Tabashnik said.
Compliance with refuge requirements, as reported to the EPA, slips yearly, he said.
His research is a warning, he said, "not the end of he game."
"Everybody is aware that insects adapt," he said. "There is no such thing as a permanent solution to insect control."