Bt corn variety OK for black swallowtails

Rcjohnsen rcjohnsen at aol.com
Sun Jul 2 20:43:29 EDT 2000


Bt corn variety OK for black swallowtails

S. Milius
   The first published field study of Bt corn and butterflies—and the first
check for any Bt-pollen risks to black swallowtails—finds no harm from a common
corn variety, say researchers of the University of Illinois at
Urbana-Champaign.
   Bt corn makes its own pesticide, thanks to genetic material borrowed from
the soil bacterium Bacillus thuringiensis. The pattern of pollen wafting from
Bt corn variety Pioneer 34R07 showed no relationship to the pattern of deaths
among black swallowtail caterpillars on nearby wild plants, report C. Lydia
Wraight, May R. Berenbaum, and their Illinois colleagues. Their paper will
appear in the Proceedings of the National Academy of Sciences.

 Plants nibbled by black swallowtail caterpillars often grow beside cornfields.
(University of Illinois)

  
   Pioneer 34R07 also seemed benign in lab tests, the researchers report, even
at concentrations of 10,000 pollen grains per square centimeter. That's 40
times as dense as the heaviest dusting researchers observed in the field.
   The black swallowtail caterpillars are not immune to Bt toxins, explains
Berenbaum. After 3 days of dining on the same high concentration of pollen from
another Bt corn, Novartis Max 454, some 80 percent of the caterpillars died.
Both varieties target European corn borers.
   The lesson of the research, Berenbaum says, is that by selecting different
genetic versions, "it may be possible to manage nontarget effects."
   Because no one has published quantitative studies of lethal doses, Berenbaum
declines to say whether black swallowtails are more or less susceptible to Bt
than are monarchs.
   Bt looked like a great start for a smart pesticide, with low risks to humans
and other mammals. Different Bt strains tended to zap rather focused clusters
of related insects, targeting groups of moths but sparing bees, for example.
The method's white-hat reputation was muddied last May by a Cornell University
study showing that in the laboratory, nearly half of young monarch caterpillars
died after 4 days of eating leaves dusted with Bt pollen (SN: 5/22/99, p. 324).
Ever since, researchers have been scrambling to find out what happens outside
the laboratory.
   A workshop last November and presentations at the Entomological Society of
America's annual meeting last December released early results of field studies
of Bt effects. Overall, they looked encouraging for the method, but none has
been published.
Berenbaum and her colleagues tested black swallowtails because they, like
monarchs, favor plants abundant beside crop fields and fencerows. Also,
Berenbaum has devoted 25 years to studying the species. Support for the project
came from a university fund for environmental research.
   The Bt corn the researchers studied gets its pest-killing power from a
genetic construct called Monsanto event 810. The researchers arrayed the
caterpillars' food plants, wild parsnips, at five distances from the field,
from 0.5 to 7 meters. They then tucked young caterpillars among the leaves of
each plant and set out glass slides smeared with Vaseline to monitor how much
pollen landed.
   Plenty of caterpillars died, as expected for a field-side jungle harboring
spiders and other dangers. However, the deaths didn't taper off with the pollen
density or distance from the field. Hence, the researchers say, pollen wasn't
an issue.
   "It's an excellent study," says John E. Losey of Cornell, a coauthor of the
monarch study that ignited the recent fuss. He welcomes the data on a second
species but cautions that pesticide susceptibility arises in complex patterns.
"It's too early to make sweeping generalizations," he says.
   Linda S. Rayor, another Cornell coauthor of the monarch paper, greeted the
swallowtail study as much-needed ecological research. Rayor's subsequent work
on Bt corn, not yet published, supports the idea that "there's a big difference
in varieties."
   Demanding a pesticide that affects only the targeted villains may be a
hopeless quest, Berenbaum muses. "The plain fact of the matter is that growing
food has nontarget effects—plowing has nontarget effects," she says. "Our
challenge is to minimize them."
References:

Losey, J.E., L.S. Rayor, and M.E. Carter. 1999. Transgenic pollen harms monarch
larvae. Nature 399(May 20):214.

Wraight, C.L. . . . and M.R. Berenbaum. In press. Absence of toxicity of
Bacillus thuringiensis pollen to black swallowtails under field conditions.
Proceedings of the National Academy of Sciences.

Further Readings:

Hansen, L. 1999. Non-target effects of Bt corn pollen on the Monarch butterfly
(Lepidoptera: Danaidae). Available at
http://www.ent.iastate.edu/entsoc/ncb99/prog/abs/D81.html.
Milius, S. 1999. BT-corn pollen can kill monarchs. Science News 155(May
22):324.
Sources:

May R. Berenbaum
Department of Entomology
University of Illinois, Urbana-Champaign
320 Morrill Hall
505 South Goodwin
Urbana, IL 61801
John E. Losey
Department of Entomology
Comstock Hall
Cornell University
Ithaca, NY 14853
Linda S. Rayor
Department of Entomology
Comstock Hall
Cornell University
Ithaca, NY 14853
>From Science News, Vol. 157, No. 24, June 10, 2000, p. 372.

       


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