Dr. Paula J. Schlax asked for comments on the Bt genes in corn and their
effects on butterflies. The following comments were sent to me by Martina
McGloughlin, head of the Biotech program at U. C. Davis. I got permission
to forward them to the group. Her comments are consistent with my own
knowledge and experience in this area.
csgasser at ucdavis.edu
>For those of you who are not interested I apologize for sending this but as
>I have received many queries, I thought that sending a general reply with
>points to consider might be of help.
>>>BIO TALKING POINTS RE MONARCH BUTTERFLY BT CORN POLLEN
>>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
>mitigate all the factors that have a significant negative impact on their
>>With this letter by John Losey to Nature (20 May), 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
>>1. Reports of the potential for effects from these BT corn hybrids on
>Monarch butterflies or other lepidoptera are not new. They have been
>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.
>>2. EPA has been provided data on the potential for impacts on non target
>species from BT pollen for years. Their analyses indicated that, when
>with the numerous other relevant factors, the impacts from such pollen were
>likely to be negligible.
>>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).
>>3. These experiments were done in a laboratory with hand application
>of the pollen. So there is a question of density, length of application and
>relevance of methods. Monarch migration and egg laying patterns ensure that
>period of larval feeding and growth throughout nearly all the Monarch range
>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
>actual potential for any negative impact is negligible.
>>4. Ongoing monitoring by companies of Bt corn fields, since their
>introduction, also shows that insect biodiversity and population densities
>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
>to significant improvements to environmental quality for, among others, insect
>eating birds and small mammals, water quality, etc.
>>5. It should be noted that techniques are being developed that would
>the next generation of crops containing Bt and other methods to protect crops
>against insect pests to contain components 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.
>>MONARCH - Specific STUFF
>>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 butterfliesí
>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%. 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
>>Automobile related mortality
>Martina McGloughlin Ph. (530) 752-3260
>Director Fax. (530) 752-4125
>Life Sciences Informatics Program http://lsi.ucdavis.edu>Biotechnology Program http://www.biotech.ucdavis.edu>355 Briggs Hall E-mail:
>mmmcgloughlin at ucdavis.edu>UC Davis
>One Shields Avenue
>Davis, CA 95616