OAFT News: Monarch Butterfly Researchers Urge Caution in Over-Interpreting Results

Academic Researchers and Industry Associations Agree Reports on Bt Crop Impact on Monarch Butterflies Overblown

WASHINGTON, D.C. (June 10, 1999) – Several academic experts have urged caution when interpreting the results of a preliminary laboratory study at Cornell university on the effect of Bt corn pollen on the Monarch butterfly that was published as a letter in the journal Nature (5/20/99). These university researchers stressed that the monarch study did not represent natural conditions and that extensive environmental research has confirmed the safety of Bt corn on non-target insects, such as the ladybird beetle, honeybee and the green lacewing, in the natural environment.

Dr. John Losey, the Cornell University entomology professor who conducted the research said, ‘Our study was conducted in the laboratory and, while it raises an important issue, it would be inappropriate to draw any conclusions about the risk to monarch populations in the field based solely on these initial result.’

In a response letter published in Nature (6/3/99), Dr. John Beringer, professor at the University of Bristol’s School of Biological Science in the United Kingdom and chairman of the U.K. Advisory Committee on Releases to the Environment, wrote, ‘There is a need for scientific rigour in the presentation of the information to ensure that it is not misrepresented … preliminary observations should not be over-interpreted’.

We want to make sure that the monarch is protect, and we want to verify the belief of numerous scientists that Bt pollen is not putting the monarchs at significant risk,’ said Dr. L. Val Giddings, vice president for food and agriculture, Biotechnology Industry Organization (BIO).

Factors in field reduce likelihood of monarch exposure to corn pollen

By design, the Cornell researchers did not match the conditions that would be present in a natural setting. In the laboratory, the caterpillars were given no choice but to feed on one treatment, in this case leaves dusted with corn pollen. In the field, the caterpillars may move about and may avoid ingesting pollen.

Under natural conditions, monarch larvae feed primarily on milkweed. Most researchers consider it likely that most milkweed does not grow close enough to corn fields to be exposed to significant amounts of corn pollen. According to an Iowa State University study by Laura Hansen and Dr. John Obrycki, the majority of corn pollen stays within the cornfield in a natural setting. The Iowa State study found that pollen density decreases by 70 percent a the edge of a cornfield, and by 90 percent three meters away from the edge of the cornfield.

Further, the majority of monarch larvae feed on milkweed when corn pollen is not present. Corn plants producer or ‘shed’ pollen for a short period of time (typically most pollen is produced in a given field over a 5-10 day period.) Based on known migration behavior, even in those regions in which corn and monarchs co-habitate, only a small portion of the monarch population will be present when corn is shedding pollen.

For these reasons – – the location of milkweed outside the range of most pollen drift, and minimal overlap between monarch feeding and pollen shedding – it is likely that the vast majority of monarch larvae throughout their range over a growing season are never exposed to corn pollen in nature at all.

Bt Corn Benefits Non-target Insects

The Bt corn crops that are currently on the market were developed to control the European Corn Borer. Prior to the introduction of Bt corn, farmers controlled European Corn Borer with conventional insecticide sprays that are toxic to monarch butterfly larvae and other desirable, non-target species. By reducing the use of these insecticides, Bt corn reduces the potential to harm non-target species, and reduces impacts of agricultural inputs on the environment in general.

‘I still think the proven benefits of Bt corn outweigh the potential risk,’ stated Dr. Losey. ‘We can’t forget that Bt corn and other transgenic crops have a huge potential for reducing pesticide use and increasing yields.’

Dr. Chris DiFonzo, Michigan State University Field Crops Entomologist & Pesticide Education Coordinator, said ‘Bt corn is a much safer method of pest management, and has less detrimental impact on all aspects of the environment — monarch included — than the use of broad-spectrum insecticides.’

‘When you consider the monarch butterflies in context with the widely recognized benefits of Bt crops, it’s clear that trends in agriculture will only help the monarchs and the environment overall, said BIO’s Val Giddings, ‘For example, Bt crops preserve beneficial insects that prey on harmful insect pests, thus limiting the need for additional insecticide sprays. Growers planting Bt crops have dramatically reduced the damage done by harmful pests and have reduced handling and exposure of insecticides on the farm.’

‘As conservation groups have noted, the primary threat to the monarch butterfly is the loss of crucial winter habitat in southern California and central Mexico,’ Giddings added. ‘Other threats come from habitat degradation along butterfly migratory routes, pesticides, and other human activities. It’s not an exaggeration to say more monarchs succumb to high-velocity collisions with car windshields than ever encounter corn pollen.’

In addition to the extensive number of field studies that have been conducted to determine the effect of Bt crops on beneficial insects, BIO and the American Crop Protection Association are working along with industry partners to address and evaluate these issues further. The available information strongly supports the advantages of Bt crops on beneficial insect population relative to the use of insecticides.

For further information on this subject, contact the following independent experts:

Warren Stevens, Ph.D
Missouri Botanical Garden
4344 Shaw Blvd, St. Louis, MO 63110-2291
(314) 577-5103

Albert Tenuta, Ph.D.
Pest Management Specialist and Plant Pathologist
Ontario Ministry of Agriculture, Food and Rural Affairs
Ridgetown Campus, University of Guelph
Ridgetown, Ontario
(519)674-1617