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Friday, March 12, 2010 |
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Potential Impact of Bt Corn Hybrids on Monarch Butterfly Larvae
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Addressing the numerous threats to Monarch butterfly populations will require joint efforts coordinated among many different groups. Industry is committed to working with groups involved with the conservation of Monarch butterflies to mitigate all the factors that have a significant negative impact on their populations. Scientific correspondence published in the journal Nature (20 May 1999) asserts that pollen from Bt corn can negatively affect growth and survival of the larvae of the Monarch butterfly. BIO offers the following points in response:
With this letter by John Losey to Nature, old issues have been resurrected to raise questions about the potential for impacts by pollen containing anti pest compounds derived from the soil bacterium BT on Monarch butterflies. Industry is fully committed to exploring the significance of this report.
- Reports of the potential for effects from these Bt corn hybrids on Monarch butterflies or other lepidoptera are not new. They have been reported in the scientific literature and/or regulatory review documents since at least 1986. The key issue is how large an impact is likely, and how significant would such an impact be when compared with the numerous other significant factors known to have impacts on Monarch ranges and numbers.
- EPA has been provided data on the potential for impacts on non target species from Bt pollen for years. Their analyses indicated that, when compared with the numerous other relevant factors, the impacts from such pollen were likely to be negligible.
- Declining Monarch butterfly populations have been a concern for decades. It is known that many factors play a role in these declines. Among the major factors are the following (in approximate order of importance):
- Threats to winter habitat in the central highlands of Mexico
The principal threat to Monarch butterfly populations is widely recognized as coming from the loss of vital over-wintering habitat in the butterflies' southern winter ranges. If we wish to ensure the long term health of Monarch butterfly populations, we first need to address this critical threat.
- Use of insecticides
Typical impacts on non target insects from chemical sprays in or immediately adjacent to treated fields approach 100 percent. The reported impacts from Bt containing pollen are much less.
- Weed management practices that affect their exclusive milkweed host
- Development and changes in land use patterns along migration routes
The loss of farmland and increases in urban sprawl over the past 50 years, and the undisciplined use by backyard gardeners of various herbicides and pesticides have drastically reduced habitat favorable to Monarchs and other lepidoptera.
- Automobile related mortality
- Topical Sprays of Bt in Organic Farming
The use of topical Bt sprays in organic farming, as first suggested with respect to the use of Dipel in 1986 (Brower, L.P. Commentary: the potential impact of Dipel spraying on the Monarch butterfly overwintering phenomenon. Atala Vol. 14(1): 17-19).
- Monarch migration and egg laying patterns 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 leaves. It is thus highly likely that in the real world, outside the laboratory, Monarch larvae would never encounter any significant amounts of corn pollen. This means the real potential for any negative impact is negligible.
- 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. Bt corn thus helps enhance beneficial insect populations that would otherwise be threatened by the use of pesticidal sprays. This leads to significant improvements to environmental quality for, among others, insect eating birds and small mammals, water quality, etc.
- It should be noted that techniques are being developed that would allow the next generation of crops containing Bt and other methods to protect crops against insect pests to contain ingredients that are expressed only in the tissues that the insect pests themselves eat. The current generation of Bt corn is aimed at reducing crop losses to an imported pest from Europe, the European corn borer. This pest eats corn stalks. Varieties of corn are already under development that could express BT or other genes of similar effect only in corn stalks, and not in pollen. Such corn varieties would eliminate entirely any risks to non target organisms that might come from Bt-containing pollen, while also allowing us to maintain the advantages of avoiding chemical pesticide sprays.
Back to Bt Corn and Monarch Butterflies Page
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