FIELDS where genetically modified cotton plants spring up as weeds in other
crops could provide refuge for the cotton boll weevil, warn entomologists in
South Carolina. That could mean the return of this major pest to parts of the
American cotton belt from which it has been eradicated.
The state spent $1.3 million eradicating the weevil, only finishing
the job in 1995. Now growers are afraid the pest could make a comeback if
farmers ignore GM cotton 鈥渨eeds鈥� growing among their other crops.
Researchers in South Carolina first noticed the problem last year in a dozen
fields of GM soybeans where GM cotton had been grown the previous year. Both the
cotton and the soybeans are resistant to Roundup, the wide-ranging weedkiller
made by Monsanto of St Louis, Missouri.
Advertisement
This means that when farmers apply Roundup to kill weeds in newly planted
fields of GM soybeans, it doesn鈥檛 destroy stray GM cotton plants left over from
the previous year. 鈥淚 could look across soybean fields and see hundreds of these
cotton plants,鈥� says Mitchell Roof, an entomologists at Clemson University,
South Carolina, who sits on a technical panel looking for an answer to the
problem.
South Carolina got rid of the boll weevil by setting up a state-wide
eradication programme organised by the South Carolina Cotton Growers鈥�
Foundation. Now, whenever farmers plant a field of cotton, they must inform the
eradication programme. Programme staff will set weevil traps dosed with weevil
pheromones around the fields.
Other crops are exempt, however, and it took a while for anyone to realise
that cotton weeds in soybean fields might be a threat. And although most of the
Roundup-resistant cotton is also genetically engineered to protect itself by
making a natural pesticide called the Bt toxin, the toxin does not always kill
the weevil.
Even a few unmonitored fields could be disastrous. Single female weevils can
lay up to 200 eggs on cotton bolls, so it would only need a few infested plants
to give the weevils a foothold. Last year, scouts with the eradication programme
spotted and treated 12 fields containing the rogue cotton. This year, they are
warning GM soybean and corn farmers who planted cotton last year to watch for
these weedy insurgents and to request weevil traps if necessary.
Randy Lynch, a supervisor with the state鈥檚 eradication programme in Sumter,
warns that if the weevils re-emerge they could spread fast. 鈥淔armers have to pay
attention to where cotton was planted last year,鈥� he says.
Roof, meanwhile, stresses that extra vigilance is a small price to pay for
the benefits of GM cotton. Beneficial insects such as ladybirds, which kill
pests, have returned in droves to the fields where the GM cotton is grown.
Coupled with the effects of the Bt toxin, this has let farmers reduce the
typical number of pesticide applications from 14 to 2 per season. 鈥淭he pluses
far outweigh the minuses,鈥� he says.