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Bt corn does not threaten the overall health and well-being of monarch butterflies, according to several recent studies.

The idea that Bt corn did pose a threat to butterflies took flight in 1999, when Cornell University researchers found, in a laboratory study, that monarch larvae could be harmed or killed if they ate large amounts of Bt corn pollen.

Since then, however, a series of lab and field studies have shown that Bt corn poses little or no threat to monarchs. For example, in 2001, a consortium of federal, university and industry scientists led by the USDA’s Agricultural Research Service (ARS) wrapped up two years of research on this question. Their conclusion, in a paper published in the Proceedings of the National Academy of Sciences: the impact of Bt corn on monarch populations is “negligible.” In fact, these researchers estimated that no more than 500 in a million caterpillar larvae would die from eating corn pollen deposited on milkweed growing near cornfields.

In October 2001, the Environmental Protection Agency (EPA) renewed for seven years registrations for varieties of Bt corn. The EPA, which approved the crop in 1995, 1996 and 1998, concluded that Bt corn “does not pose risks to human health or to the environment.”

So, what accounts for the different impressions left by the research findings? It really boils down to overall study design and assessing risk, based on actual hazard (toxicity) and exposure under field conditions.

Real-world research

Bt corn refers to corn that has been enhanced through biotechnology to produce its own insecticidal protein to protect it from the European corn borer, an insect pest that can have devastating effects on corn crops. The “Bt” in the crop’s name refers to Bacillus thuringiensis, a common, naturally occurring soil bacterium, the genes of which have been added to the corn plant.

Monarch caterpillars dine exclusively on the leaves of milkweed plants, which typically grow in ditches in and near cornfields. Every year, corn sheds pollen over a one- to two-week stint, and the concern was that Bt pollen settles on to milkweed leaves, and could impact monarch larvae.

However, when Cornell University researchers conducted their 1999 study, they did not attempt to duplicate real-world environmental conditions. Rather, they used only a small number of caterpillars and gave them no choice but to eat leaves coated with a thick layer of Bt corn pollen. The study’s lead researcher, Dr. John Losey, noted:  “. . . Our study was conducted in the laboratory. . . it would be inappropriate to draw any conclusions about risk to monarch populations in the field based solely on these initial results.”

Consequently, subsequent research projects were structured to account for real-world conditions. For example, the study designed by the team of scientists working with the ARS focused on answering two key questions:

• How much Bt corn pollen does it take to have a toxic effect on caterpillars?

• How likely is it that caterpillars might be exposed to that much pollen?

The findings revealed that monarch caterpillars have to be exposed to pollen levels greater than 1,000 grains/cm2 to show toxic effects. In addition, the study also found that corn pollen levels on milkweed leaves in corn fields averaged only about 170 grains/cm2 — well below the toxic level. Several similar field studies reported much lower pollen concentrations. In Maryland, concentrations were highest — 50 grains/cm2 — at the edge of the cornfield. In Nebraska, pollen concentrations ranged from six grains/cm2 at the field edge to less than one grain/cm2 beyond 10 meters.

The primary reason for these low pollen concentrations is that corn pollen grains are fairly heavy, therefore most settle in the immediate vicinity of the cornfield. Though wind can carry the pollen away from the field, it is deposited over a large area so that concentration of pollen on surfaces remains very low. As a result, monarch exposure to Bt pollen is essentially limited to larvae that develop within or very near to Bt corn. In addition, field studies demonstrated that such factors as rain and morning dew affect pollen’s ability to adhere to leaves and that pollen is degraded by sunlight.

Helping matters even more is the fact that several Insect Resistance Management (IRM) techniques are in place to preserve the benefits of Bt corn technology.10 Among these is a field-layout option in which several rows of non-Bt corn are planted around the perimeter of Bt corn fields, thereby reducing corn pollen migration.

The outlook for monarchs

Now that researchers have answered the questions regarding the immediate risks Bt pollen poses to monarchs, they’ve turned their attention to the subtle effects that could occur from longer-term exposure. Even so, it’s clear that the monarch, which is neither an endangered nor a threatened species, is exposed to far greater risks in the natural world.

In January 2002, for example, tens of millions of monarchs were killed by a winter storm in their Mexican wintering sites. (In a phenomenon still not fully understood by scientists, millions of North American monarchs migrate up to 3,000 miles each year to Mexico.) Initial analysis of the mass die-off — up to 80 percent of the colonies may have been lost — suggested that the diminished forest cover caused by deforestation contributed significantly to this catastrophic event.

In addition to habitat destruction, monarch populations also are depleted by mowing along highways, ditches and pastures, which destroys milkweed. Collisions with cars and trucks — road kill — also take a toll. But the most common killer of monarchs is other hungry insects. All told, less than 10 percent of caterpillars ever reach adulthood.

So based on laboratory and field studies conducted by the scientific experts, the results demonstrate that Bt corn does not harm the monarch butterfly. Higher-yielding biotech crops, including new crops that are able to thrive in poor soil, will reduce the pressure to bring more virgin land under the plow. And that will help preserve important wildlife habitat like the degraded area in Mexico where so much of the monarch population was destroyed in January 2002.

source : whybiotech.com