Chinese, U.S. scientists make first reversal of pest resistance to GM cotton

The issue of pest resistance to genetically modified (GM) crops has received widespread attention, and researchers from China and the United States revealed on Monday the success of a surprising new strategy for countering this problem.

In a study published in the U.S. journal Proceedings of the National Academy of Sciences, they reported that hybridizing genetically engineered cotton with conventional cotton reduced resistance in the pink bollworm, a voracious global pest.

The findings were based on an 11-year study, in which researchers at the Chinese Academy Of Agricultural Sciences (CAAS) and the University of Arizona (UA) tested more than 66,000 pink bollworm caterpillars from China's Yangtze River Valley, a vast region of southeastern China that is home to millions of smallholder farmers.

According to the study's authors, this is the first reversal of substantial pest resistance to a crop genetically engineered to produce pest-killing proteins from the widespread soil bacterium Bacillus thuringiensis, or Bt.

"This study gives a new option for managing resistance that is very convenient for small-scale farmers and could be broadly helpful in developing countries like China and India," study coauthor Kongming Wu, who led the work conducted in China and is a professor in the CAAS's Institute of Plant Protection in Beijing, said in a statement.

Crops genetically engineered to produce insecticidal proteins from Bt kill some major pests and reduce use of insecticide sprays.

However, evolution of pest resistance to Bt proteins decreases these benefits.

The primary strategy for delaying resistance is providing refuges of the pests' host plants that do not make Bt proteins. This allows survival of insects that are susceptible to Bt proteins and reduces the chances that two resistant insects will mate and produce resistant offspring.

Before 2010, the U.S. Environmental Protection Agency required refuges in separate fields or large blocks within fields.

Planting such non-Bt cotton refuges is credited with preventing evolution of resistance to Bt cotton by pink bollworm in Arizona for more than a decade.

By contrast, despite a similar requirement for planting refuges in India, farmers there did not comply and pink bollworm rapidly evolved resistance.

The new strategy used in China entails interbreeding Bt cotton with non-Bt cotton, then crossing the resulting first-generation hybrid offspring and planting the second-generation hybrid seeds.

This generates a random mixture within fields of 75 percent Bt cotton plants side-by-side with 25 percent non-Bt cotton plants.

"We have seen blips of resistance going up and down in a small area," said senior author Bruce Tabashnik, a professor in the UA's College of Agriculture and Life Sciences. "But this isn't a blip. Resistance had increased significantly across an entire region, then it decreased below detection level after this novel strategy was implemented."

Tabashnik called this strategy revolutionary because it was not designed to fight resistance and arose without mandates by government agencies. Rather, it emerged from the farming community of the Yangtze River Valley.

"For the growers in China, this practice provides short-term benefits," Tabashnik added. "It's not a short-term sacrifice imposed on them for potential long-term gains. The hybrid plants tend to have higher yield than the parent plants, and the second-generation hybrids cost less, so it's a market-driven choice for immediate advantages, and it promotes sustainability." Enditem