Disappointing but not unexpected is a leading UK
scientist's reaction to news of what is claimed to be the first
instance of in-field resistance to the GM-derived insect defences
of a crop.
"The sky won't fall in but it's disappointing," said Ian
Denholm, head of Rothamsted
Research's Department of Plant and Invertebrate Ecology.
He was commenting on an
Independent newspaper
report on research at the
University of Arizona which
found bollworm
moth caterpillars resistant to the toxin from the
Bacillus
thuringiensis (Bt) gene that is widely used in creating
pest-resisting GM species.
"Evolution in action"
According to the report, the resistant caterpillars were found
in 12 cotton fields in
Mississippi and
Arkansas during surveys from
2003 to 2006, and research team leader Bruce Tabashnik is quoted as
saying: "What we are seeing is evolution in action. This is the
first documented case of field-evolved resistance to a Bt
crop."
Since introduced in the early 2000s Bt crops have become widely
grown throughout the world, noted Dr Denholm. "They have been
spectacularly successful.
"We have always known that it was relatively easy to select for
resistance [to the Bt toxin] in the laboratory. But we haven't seen
it in the field because these crops are very carefully
regulated."
This included the requirement to provide refuge areas allowing
susceptible species to survive and mate with any becoming
resistant, he explained.
More than one available
As with resistance to conventional insecticides, the development
of resistance to the Bt toxin was not unexpected, he said.
"But it's not the only one available. There are three or four
others, although they are all based on Bt.
"If this latest finding is confirmed there will need to be some
kind of re-think on strategy and possibly a change to some of these
others."
Monsanto's Colin Merritt
points out that Randy Luttrell, of the University of Arkansas,
measured the susceptibility of cotton bollworm to the
Cry1Ac protein (in
Bollgard cotton) between 1992 and 2007.
Interpretations
"Dr Luttrell presented his data at the recent 2007
Entomological Society of
America meeting and concluded there is variation in bollworm
response to the Bt protein, but the data do not support a
conclusion of resistance."
Dr Tabashnik's review of the data is published in the February
2008 issue of Nature
Biotechnology.
"Entomologists in the cotton industry disagree with the
interpretation of the data Tabashnik has made," says Dr
Merritt.
"Our understanding is that
Environmental Protection Agency
also disagrees with his interpretation.
"During the use of Bt as a spray for many decades, as well as in
GM crops for 10 years, isolated strains of insects have shown
slight variations in response. But the fact that field performance
has not been affected shows the technology remains a robust
alternative to chemical methods."
Picture courtesy of Clemson University, Department of
Entomology.