Ithaca, New York
June 3, 2008
Genetically modified (GM) plants
that use Bt (Bacillus thuringiensis), a common soil bacterium,
to kill pests won't harm the pests' natural enemies, according
to
new research by Cornell
University entomologists.
That is welcome news for ecologists and farmers in the debate
over GM plants. Much of the debate surrounding the use of GM
crops focuses on their effect on organisms that aren't pests.
The research showed that GM plants expressing Bt insecticidal
proteins are not toxic to a parasite that lives inside the
caterpillar of the diamondback moth, a devastating worldwide
vegetable pest. It was published in the May 27 issue of the
online scientific journal PLoS One.
"The conservation of parasites is important for enhancing
natural biocontrol that will help suppress pest populations as
well as reduce the potential for the pest insects to develop
resistance to the Bt,"
explained Anthony Shelton, Cornell professor of entomology at
the New York State Agricultural Experiment Station in Geneva,
N.Y., who conducted the study with postdoctoral associate Mao
Chen. "Our studies make it clear that Bt plants are a win-win
situation to control pest insects and to enhance biocontrol and
biodiversity."
The Bt bacterium, which is not harmful to humans, has been used
for decades as a leaf spray and since 1996, in GM plants, a
method that has proven much more effective and is now more
widely used. Both uses are approved by the U.S. Environmental
Protection Agency. In 2007, Bt corn and cotton plants were grown
in 22 countries on 104 million acres, according to Shelton.
"Few studies have examined the effect of Bt plants on parasites
of caterpillars, but some of them have reported negative
impacts," said Chen, noting that the new research suggests that
those negative findings were likely due to testing methods.
To separate out the effect of insecticides and Bt proteins on
the caterpillar and parasite, the Cornell researchers isolated
and bred strains of caterpillars that were resistant to Bt or a
conventional or organic insecticide. Then the caterpillars were
parasitized with a wasp that kills the caterpillar in nature.
The resistant caterpillars were then either fed GM plants
expressing the Bt protein or non-GM plants sprayed with the Bt
protein, conventional insecticides or organic insecticides.
The parasitized caterpillars that ate plants treated with
conventional and organic insecticides to which they were
resistant, survived and developed into moths because the
parasite was killed by the insecticide the caterpillar ingested.
However, when the caterpillar fed on the Bt-sprayed plants or Bt
plants, the parasite was not affected and killed its host
caterpillar when it emerged as an adult wasp, showing that Bt
plants are not toxic to the parasite.
Other Cornell researchers involved in the study include
Elizabeth Earle and Jun Cao from the Department of Plant
Breeding and Genetics and Jian-Zhou Zhao and Hilda Collins from
the Department of Entomology. The work was supported by a grant
from the USAID Program for Biosafety Systems.
Un estudio confirma que las plantas Bt no afectan a
los insectos beneficiosos |
Source:
Fundación Antama
Un nuevo estudio realizado por científicos de la
Universidad estadounidense de Cornell (Nueva York)
confirma que las plantas transgénicas tipo Bt sólo
tiene efecto insecticida contra las plagas que comen
la planta y no contra los insectos beneficiosos que
son enemigos naturales de las plagas, según informa
PlosGenetics en su página web.
Según el informe, los insectos observados han sido
la polilla de dorso de diamante de las coles,
denominada Plutella Xylostella, y un importante
endoparastoide de la misma, la pequeña avispa
Diadegma insulare, que pone los huevos dentro de la
larva de la polilla, donde se desarrollan sus
propias larvas. En el estudio se han utilizado
polillas resistentes a la proteína Bt y a
insecticidas convencionales y de la agricultura
ecológica, siendo parasitados por Diadegma insulare
y alimentadas con plantas de brécol convencional y
transgénico Bt.
Las larvas que comieron plantas tratadas con
insecticidas a los que eran resistentes, sean estos
convencionales o ecológicos, sobrevivieron debido a
que estos isecticidas tenían efecto sobre las
avispas parásitas. No obstante, en plantas tratadas
con toxina Bt o plantas OMG tipo Bt el parásito no
se vió afectado, demostrando que el Bt no es tóxico
para el parásito. |
By Marissa Fessenden |
|