Scientists Find Genetic Basis Of Insect's Resistance To Engineered Crops

Now, a team of geneticists has identified a gene that confers high levels of resistance in a common agricultural pest – a discovery which will allow farmers and government officials to take early steps to prevent uncontrollable outbreaks.

The scientists published their findings in the Aug. 3 issue of the journal Science.

The geneticists, from North Carolina State University, Clemson University and the University of Melbourne, studied the DNA of the tobacco budworm moth (Heliothis virescens), which feeds on a variety of crops and has developed resistance to most conventional chemical insecticides.

"Not only will knowledge about this gene enable us to detect the early signs of pests evolving resistance to the current engineered plants, it may also allow us to modify the plants so they will be defended against the new pest strains," said Dr. Fred L. Gould, the William Neal Reynolds Professor of entomology at NC State and a co-author on the Science paper.

Specifically, the researchers located the recessive gene (BtR-4) that confers much of the resistance in the moth to natural toxin from the soil bacterium called Bacillus thuringiensis (Bt). Several crops – including cotton, which is a host plant for the moth's larvae – have been genetically encoded with the insecticidal Bt toxin, which kills all budworm moths except rare individuals that contain a pair of the recessive genes.

The popular Bt crops give farmers a tool for controlling pests like the tobacco budworm moth while reducing the need for potentially dangerous chemical pesticides. But some people, including organic farmers who have long used naturally produced Bt bacteria for controlling pests, worry that the new, genetically altered crops could cause pests to rapidly develop resistance to naturally produced Bt toxins as well as the transgenic Bt toxins, leaving farmers without a reliable organic pest-control agent.

To address these concerns, the Environmental Protection Agency requires that cotton farmers plant at least 4 percent of their fields with non-modified cotton to ensure the dominant genes of susceptible moths remain common in moth populations.

While resistant budworm moth strains have not yet caused damage in the field, previous research by Gould and his colleagues established that 1.5 of every 1,000 moths carry one of the genes for resistance to the Bt toxin. Based on this frequency of resistance, the researchers predicted that it would likely take about 10 years for Bt resistance in budworm moths to become a problem if Bt cotton was widely planted. Those results assume that cotton farmers are complying with the EPA's "high-dose/refuge" mandate.

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