ENGINEERED CORN CAN KILL MONARCH BUTTERFLIES Agnet May 19, May 19,
1999 Cornell University News Service Ithaca, N.Y.

An increasingly popular commercial corn, genetically engineered to
produce a bacterial toxin to protect against corn pests, has an unwanted
side effect: Its pollen kills monarch butterfly larvae in laboratory tests,
according to a report by Cornell University researchers. Writing in the
latest issue (May 20) of the journal Nature, the Cornell researchers note
that this hybrid crop, known as Bt-corn, has genes from the bacterium
Bacillus thuringiensis (Bt) spliced into the plant genes. These hybrids are
very effective against the ravenous European corn borer, a major CORN pest
that is destroyed by the plant's toxic tissue. The engineered corn is safe
for human consumption.
Unlike many pesticides, the Bt-CORN has been shown to have no effect
on many "nontarget" organisms - pollinators such as honeybees or beneficial
predators of pests like ladybugs. But the Bt-modified corn produces pollen
containing crystalline endotoxin from the bacterium genes. When this corn
pollen is dispersed by the wind, it lands on other plants, including
milkweed, the exclusive food of monarch caterpillars and commonly found
around cornfields.
Like all grasses, CORN is wind-pollinated, and the pollen can be
blown more than 60 yards from the edge of cornfields. "Pollen is that
yellow dusting your car gets on spring and summer days; pollen is
everywhere," says John E. Losey, Cornell assistant professor of entomology
and the primary investigator on the study. "That's why we are concerned
about this problem."
Other researchers on the study were Linda S. Rayor, Cornell instructor
in entomology, and Maureen E. Carter, Cornell research aide. "Monarchs are
considered to be a flagship species for conservation. This is a warning
bell," says Rayor. "Monarchs themselves are not an endangered species right
now, but as their habitat is disrupted or destroyed, their migratory
phenomena is becoming endangered." In the laboratory tests, monarchs fed
milkweed leaves dusted with so-called transformed pollen from a Bt-corn
hybrid ate less, grew more slowly and suffered a higher mortality rate, the
researchers report. Nearly half of these larvae died, while all of the
monarch caterpillars fed leaves dusted with nontransformed corn pollen or
fed leaves without corn pollen survived the study.
The toxin in the transformed pollen, the researchers say, goes into
the gut of the caterpillar, where it binds to specific sites. When the
toxin binds, the gut wall changes from a protective layer to an open sieve
so that pathogens usually kept within the gut and excreted are released
into the insect's body. As a result, the caterpillar quickly sickens and
dies. Bt-engineered CORN is among the first major commercial successes for
agricultural biotechnology. Last year, more than 7 million acres of the
hybrid crop were planted by U.S. farmers primarily to control the European
corn borer. Before the advent of Bt-corn, this pest was extremely difficult
to control because it bores into the stalk, where it is protected from
pesticides. It produces several generations a year. Because it was so
difficult to control effectively with pesticides, annual losses averaged
$1.2 billion. In contrast,Bt-corn provides essentially total season-long
control at a reasonable cost without the use of pesticides. At least 18
different Bt-engineered crops have been approved for field testing in the
United States. As of last year, transformed corn, potatoes and cotton had
been approved by the U.S. Department of Agriculture for commercial use.
Several factors make monarch caterpillars particularly likely to make
contact with corn pollen, Losey says. Monarch larvae feed exclusively on
milkweed because it provides protection against predators. The plant
contains cardenolides, which are toxic, bitter chemicals that the monarch
caterpillar incorporates into its body tissues, rendering it unpalatable to
predators. Milkweed grows best in "disturbed" habitats, like the edges of
cornfields, Losey notes.
The butterflies overwinter in Mexico and by the spring begin migrating
north. The first generation of the year crosses into Texas, other Gulf
Coast states and Florida, seeking milkweed on which to lay their eggs and
feed. By late May or early June, the second generation of adults has
emerged and heads north to areas including the Midwest Corn Belt. Monarch
caterpillars are feeding on milkweed during the period when corn is
shedding pollen, Losey says. Thus "they may be in the right place at the
right time to be exposed to Bt-corn pollen."
Says Losey: "We need to look at the big picture here. Pollen from
Bt-corn could represent a serious risk to populations of monarchs and other
butterflies, but we can't predict how serious the risk is until we have a
lot more data. And we can't forget that Bt-corn and other transgenic crops
have a huge potential for reducing pesticide use and increasing yields.
This study is just the first step, we need to do more research and then
objectively weigh the risks versus the benefits of this new technology."