By David N. Leff

Monarch butterflies can breathe easier again.

The flap that implicated the striking black-and-orange winged insect erupted in the U.S. just over two years ago, when Nature dated May 20, 1999, ran a one-page item by three entomologists at Cornell University in Ithaca, N.Y. Its title set off the national brouhaha: ¿Transgenic pollen harms monarch larvae.¿ That momentous article¿s first author was Cornell entomologist John Losey.

The monarch butterfly (Danaus plexippus) lives on milkweed (Asclepias sp.), a lowly plant that grows in and along the edges of cornfields. The pollen indicted by the Cornell researchers comes from transgenic corn (Zea mays) engineered to express a protein secreted by the soil bacterium Bacillus thuringiensis. That protein is a crystalline toxin lethal to many species of insects, from mosquitoes to the European corn borer (Ostrinia sp.). That pest causes $1 billion in crop damage annually in the U.S.

Except for herbicide-tolerant soybeans, Bt corn is the most widely grown transgenic crop plant in the U.S. In 1999, it was sown on 9.6 million hectares (over 3,885,000 acres).

In laboratory experiments, the Cornell entomologists fed monarch larvae on Bt corn pollen dusted onto their favorite fodder, milkweed. The resulting die-off of the larvae led the authors to warn: ¿These results have potentially profound implications for the conservation of monarch butterflies.¿

Americans cherish these gorgeous winged insects on a par with their love of bald eagles, observed May Berenbaum, who heads the department of entomology at the University of Illinois, Urbana. Monarch butterflies, she pointed out, are the state insect of Illinois (as they are of Minnesota).

Berenbaum is senior author of a paper released online Friday, Sept. 9, 2001, by the Proceedings of the National Academy of Sciences (PNAS). Its title: ¿Effects of exposure to event 176 Bacillus thuringiensis corn pollen on monarch and black swallowtail caterpillars under field conditions.¿ Hers is one of six parallel papers made electronically public Friday by PNAS. Cornell¿s Losey, interestingly, is a co-author of one paper.

Online Release Forecloses Publication Date

Initially, the six papers were slotted for journal publication on Oct. 2, 2001. ¿What I knew of this,¿ Berenbaum recounted, ¿I heard about only last Thursday. There was a communication from the Environmental Protection Agency requesting PNAS to move up the publication date, so this information could be available to the public during the public comment period.¿

The six papers¿ co-authors are entomologists from nine states, convened by the U.S. Department of Agriculture¿s Research Service (USDA-ARS) to confirm or disprove in actual field trials the dire Cornell laboratory findings. Richard Hellmich, a USDA entomologist at Iowa State University in Ames, heads a USDA-ARS task force to oversee these field tests. Its results, he told BioWorld Today, ¿lay to rest as a major concern¿ the Cornell lab-based warnings.

Surveying the five papers other than her own, Berenbaum summed up: ¿There¿s one paper that¿s a lab assay. Another examines temporal overlap between occurrence of larvae and occurrence of pollen. A third paper looks in different localities in the cornfield to assess the actual field impact. Our paper looked at one particular event that impacts on both black swallowtail butterflies and monarchs ¿ comparing those two different species.¿

Berenbaum, a member of the National Academy of Sciences, edited and submitted the six papers, which were all received by PNAS Aug. 17. She told BioWorld Today, ¿I don¿t think that Bt corn poses a clear and present danger to the monarch butterfly,¿ adding, ¿It¿s not even considered an endangered species.¿ However, she made the point that of the six, her paper was one of several to report a negative effect on what she termed ¿America¿s iconic insect.¿ Other papers dismissed the Cornell results as ¿negligible.¿

Her field experiment tested a specific variant of the insecticidal Bt crystalline toxin, called ¿Novartis Cry 176.¿ ¿This variety of Bt corn,¿ she explained, ¿is known to produce pollen with higher concentrations of the pesticide than other versions. It has been linked to a reduced survival of monarchs at concentrations naturally occurring in and near cornfields.¿

The effect of a given Bt variant is known as a ¿Cry event¿ ¿ Cry for crystalline.

¿When a plant is genetically transformed,¿ Berenbaum said, ¿the investigators can¿t necessarily drop a gene into a genome with great precision. So every time one results in a plant that is expressing whatever the target protein is, that particular genetic configuration is called an event.¿

Cry Havoc¿s 176 Variety Decimates Monarchs

¿Scientists can control when and in what part of the plant the toxin is produced by combining gene sequences with specific promoters,¿ she went on. ¿Cry gene constructs differ in the promoters their corn pollen carry. These are the switches that turn the gene on, expressing the pollen in different arrays of corn tissues.

¿According to the information that we gleaned when writing up our paper,¿ Berenbaum observed, ¿Novartis Cry 176 accounted for less than 2 percent of all transgenic Bt corn planted in the 2000 growing season, so it does not constitute a major proportion of the corn crop out there. In any case, it will not be reregistered for future planting.¿

She noted, ¿Nearly half of the 600 monarch larvae exposed to Novartis 176 died within the first 24 hours. This and subsequent mortality were not associated with proximity to Bt corn, and may have been due in part to predation. We did observe large numbers of predators.¿

Hellmich cited such predators as including ¿beetles, lady bugs, stink bugs, spiders and ants.¿

Berenbaum pointed out, ¿There are many other risks that monarchs face, notably, destruction of overwintering habitat in Mexico.¿ She concluded: ¿The incremental impact of eating Bt corn pollen on overall monarch well-being is, I think ¿ at least as far as the evidence suggests ¿ not a major factor.¿

To which Lisa Dry, director of communications for BIO, the Biotechnology Industry Organization, added: ¿The Cornell lab experiment should never have been taken seriously to the extent that it was. It raised interesting questions, and these six papers in PNAS confirm that there is no risk to monarch butterflies from the Bt corn.¿