Monsanto's corn SAVES the butterfly, it DOESN'T have the BT in the pollen.
"DEKALB Genetics, now owned by Monsanto, developed hybrids with the DBT 418 event, marketed under the BtXtra brand. In these the Bt Cry1Ab toxin gene is used. This produces a slightly different toxin with different insect specificity, and it is not expressed in pollen, but only in the leaf, kernel, stalk and silk."
(Full story)
The Bowditch Group
03 June 1999
Bt Corn And Monarch Butterflies
Cornell University researchers, in a letter to the journal Nature, May 20 issue, reported that pollen from Bt corn harmed monarch butterfly larvae in laboratory tests. In the Cornell study, one group of monarch (Danaus plexippus) caterpillars fed on milkweed (Asclepias curassavica) leaves dusted with pollen from Bt corn, another group fed on milkweed leaves dusted with pollen from non-genetically-modified corn, and a third group fed on leaves without added pollen. The researchers found that the caterpillars that ate leaves with pollen from the Bt corn ate less, grew more slowly and died sooner. Results were similar to those reported earlier by Hansen and Obrycki (http://www.ent.iastate.edu/entsoc/ncb99/prog/abs/d81.html) who used leaves collected in corn fields. The Cornell researchers (Losey, Rayor and Carter, who can be contacted at jel27@cornell.edu) collected pollen and applied it to lab-raised milkweed leaves.
The Cornell researchers used pollen from Novartis Seeds' hybrid N4640-Bt, which contains the Cry1Ac Bt gene in Monsanto's Bt11 event, sold under the YieldGard brand. The hybrid is designed to be resistant to European corn borer (Ostrinia nubilalis), a common and destructive pest of corn (Zea mays). In Bt hybrids using this event, Bt toxin is produced at high levels, throughout the growing season, in the leaves, pollen, tassel, silk and kernel. This provides excellent corn borer resistance, but as the Cornell researchers discovered strong expression of the toxin gene in pollen may lead to effects on non-target insects.
Other commercial Bt corn varieties have been developed and are being marketed by a number of different companies. Although the Bt11 event and the very similar Mon 810 event, both sold under the YieldGard brand, are widely used, there are other events with different characteristics. DEKALB Genetics, now owned by Monsanto, developed hybrids with the DBT 418 event, marketed under the BtXtra brand. In these the Bt Cry1Ab toxin gene is used. This produces a slightly different toxin with different insect specificity, and it is not expressed in pollen, but only in the leaf, kernel, stalk and silk.
Bt corn was also developed by Ciba (now part of Novartis) and Mycogen (now part of Dow AgroSciences) called KnockOut or NatureGard. This also contains the toxin gene Cry1Ab, but in the event 176. In hybrids with this event, green pollen and stalk tissue produce the Bt toxin. The toxin level in tissue is high early in the growing season, and declines rapidly as the growing season progresses. This may mean that pollen of these hybrids would be harmless to monarchs, but at the same time the corn plant is exposed to more potential damage from late-season feeding by corn borers. However Hansen (lrhansen@iastate.edu ) tells us that the Bt pollen in her study was from Novartis' hybrid MAX 454, which uses the 176 event. It will be interesting to see how her continuation of this research comes out this year.
AgrEvo has recently introduced its Bt event, based on the Cry9c toxin gene. This event is also strongly expressed throughout the plant for the full growing season, but may have different specific toxicity to monarchs than the Cry1Ab toxin.
Thus there are several variables in the Bt hybrids themselves that will affect whether their pollen might be harmful to monarchs (butterflies, that is): the specific Bt toxin expressed, the location of expression, and the timing of expression. Since monarch larvae feed only on milkweed, they will only be exposed to Bt toxin if it is deposited on the leaves of milkweed plants.
Although corn is wind-pollinated, and its pollen may travel considerable distances, the vast majority of corn pollen falls very close to the plant that sheds it. The transport of corn pollen is well understood, since production of hybrid corn seed depends on cross-pollination between pollen-shedding plants and ear-bearing ones. To get adequate yields of seed these generally cannot be placed more than several meters apart. Also, it is important in hybrid seed production to isolate the production of a specific hybrid from sources of pollen of other parents, to avoid off-types in the seed product. The isolation distances necessary to reduce off-types to very low levels are well known. Research to learn the amounts of pollen that might be deposited on milkweeds by corn is under way (see Hansen and Obrycki).
Monarch butterflies are very widely distributed, in their summer breeding range. They feed on milkweed plants in open meadows and grasslands from Southern Canada south through all of the United States, Central America, and most of South America. They are also present in Australia, Hawaii, and other Pacific islands. Those in North America overwinter as adults in California and in central Mexico, and these overwintering habitats are seriously threatened. According to recent studies about half the monarchs in North America hatch and feed as larvae in a band from Nebraska to Ohio, which coincides with the "corn belt" (see Wassenaar and Hobson ,PNAS 1998 95: 15436-15439).
Milkweed is regarded as a noxious weed by farmers, and weed-control practices generally prevent it from growing among crops in fields. There are many herbicides used in field crops such as corn, soybeans and cotton that will kill milkweed. In fact, the advent of herbicide-tolerant crops, with the more complete weed control they can provide, has been noted as another potential threat to milkweed populations (see Hartzler at weeds.iastate.edu ).
Since weed control costs money, farmers do not control weeds growing where they will have no economic effect. Thus milkweed might not be welcome in a field, but is widespread in disturbed sites such as roadsides, fallow fields, uncultivated areas, and field boundaries.
Industry officials have called the Cornell study inconclusive because the researchers did not precisely measure the amount of pollen that was put on the milkweed leaves. The researchers reported that pollen density was set to visually match densities on milkweed leaves collected from corn fields, and that pollen was applied by gently tapping a spatula of pollen over milkweed leaves that had been lightly misted with water.
There are a number of other variables that should be considered. The Bt toxin is notoriously unstable to UV light. It breaks down very rapidly in sunlight. Is this also true for Bt toxin in pollen grains? What fraction of monarch larvae would be exposed to corn pollen, considering that in any specific region the corn is shedding pollen for only a week to ten days each year. If monarch larvae are emerging and feeding during that time, and no other, that would suggest a greater potential impact than if larvae emerge over a longer period, or at a different time. The laboratory studies used laboratory-raised larvae and deliberately exposed them to heavy pollen loads.
According to Dr. Val Giddings, Vice President of Food and Agriculture of the Biotechnology Industry Association, ''Monarch migration and egg laying pattern ensure that the primary period of larval feeding and growth throughout nearly all the Monarch range takes place well before any nearby corn produces pollen. Ongoing monitoring of Bt corn fields by companies since their introduction further shows that very little pollen lands on adjacent milkweed plants. . . . Ongoing monitoring by companies of Bt corn fields since their introduction also shows that insect biodiversity and population densities in Bt corn fields is significantly higher than in fields treated with chemical pesticide sprays.''
Dr. John E. Losey, Cornell assistant professor of entomology, and primary investigator on the study reported in Nature, cautions that ''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...We need to do more research and then objectively weigh the risks versus the benefits of this new technology.''
For many opponents of biotechnology, the study validates the concern that genetic modification can have unforeseen, negative effects on the environment. In response to the study, Greenpeace and the Union of Concerned Scientists are asking the Environmental Protection Agency to consider pulling genetically modified crop seeds off the market, citing broad environmental concerns. The EPA has said it will study the issue. In Europe, EU Commission officials announced that they have placed Pioneer Hi-Bred International Inc.'s application to sell Bt corn on hold, and that it will review earlier EU approvals of genetically modified corn produced by Monsanto Company and Novartis AG. The EU announcement has raised ''great concerns'' about the ability of U.S. seed companies to export, according to U.S. Commerce Secretary William Daley. While the Cornell study has damaged the public's perception of genetically modified crops, and consequently, the biotech industry, more research must be done to determine how threatening biotechnology really is to the Monarch butterfly.
The publicity surrounding the publication of the Nature letter is an example of how preliminary scientific results can be used to whip up heightened concerns among consumers, legislators and regulators. In such cases very little of the true story of the research and its context is conveyed to the concerned parties, and they have no easy way to learn more. We can expect many more of these alarms as crop biotechnology becomes more widely used. The research itself is certainly helpful in raising questions that will help guide the wise use of technology.
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