Bt Corn Benefits Non-GM Corn

A new study published in Science found that Bt corn provides economic benefits for farmers who plant non-GM corn in nearby fields. It sounds great, but is that the whole story?

Researchers studied historic data on economic damage by the European corn borer from the last fifty years and concluded that the commercial introduction of Bt corn in 1996 produced a savings of roughly $6.8 billion over fourteen years. The study further broke down the savings into that realized by Bt corn farmers and non-GM corn farmers and found that non-GM corn farmers realized 62% of those savings. But how is that possible? And why would a farmer spend the extra money on Bt corn if the benefits were going to accrue to the farmers who spent less?

The most interesting result of this study is that it shows that farmers should plant less Bt corn than they have been planting.

The European Corn Borer

The European corn borer is a small moth whose caterpillars damage the corn to reduce yield. They’re difficult to control; farmers have to visually inspect their cornfields to discover the pests. This is a problem for two reasons:Β  1) corn is itchy and no one wants to walk through that stuff and 2) cornfields are vast and the European corn borer lays its tiny eggs on the bottom of the leaf – they’re easy to miss.

Insecticides (both organic and conventional types) must be timed to the growth cycle of the corn borer. Cultural practices, such as cutting the corn stalks close to the soil and plowing them under, provide the best control of the European corn borer, cutting populations by 75%.

The main appeal of the Bt corn is that the toxin in the corn is a sort of insurance against the pest.Β  If the corn borer shows up, the pesticide is already there.Β  If it doesn’t show up, well, that’s money gone, but insurance is like that sometimes.

Bt (Bacillus thuringiensis) – Benefits and Risks

Bt (bacillus thuringiensis) is a group of naturally-occurring bacteria that produces a toxin which kills any insect that ingests it, but produces no effects on most people. (Some people have an allergic reaction to some proteins produced by some Bt – the StarLink controversy, for instance.) When introduced into corn, European corn borer caterpillars die within two days. In those two days, any predatory insect (the ones we want to keep around) that eats the caterpillar will also die. The toxin is very effective.

When Bt is used as a spray, the insecticide will quickly degrade, thereby limiting the effect on predator populations. However, with the Bt toxin genetically inserted into the corn, the presence of the toxin is constant, reducing the numbers of the pest and predators. The Bt toxin in Bt corn is so persistent, it shows up in streams near cornfields.

Heavy use of Bt can also produce resistance to the toxin. Overuse of Bt corn in Puerto Rico has given fall armyworms resistance to Bt. Bt-resistant pests have also shown up in Nebraska, Hawaii, and Florida in the United States, and also in India and China.Β  The European corn borer has developed resistance to Bt in laboratory tests, which indicates it’s a likely candidate for developing resistance in the wild.

But What About the Money?

Bt-resistance and toxicity to non-target insects are well-known problems within the agricultural community. So this study that purports amazing benefits to non-GMO adopters is causing quite a stir. Why not plant more Bt corn for even more benefits? Let’s look at the math a little more.

The study looked at five states – Iowa, Illinois, Minnesota, Nebraska, and Wisconsin – which account for about 53% of the corn grown in the United States. The total savings was $6.8 billion over 14 years due to the introduction of Bt corn. Corn growers who used Bt corn saved $2.5 billion of that.

The other $4.3 billion in savings went to the farmers who did not plant a GM corn variety. Bt corn costs more than conventional hybrid corn: $1.7 billion more over the fourteen years of the study. The other $2.6 billion in savings came from the suppression of the European corn borer, which is the source of the savings for the Bt corn growers.

Refuges for Pest Management

So not only did farmers who eschewed GMOs pay less for their seed corn upfront, they also reaped identical benefits in fewer outbreaks of corn borers. This indicates the benefit of β€œrefuges” – fields of corn without the Bt gene inserted where pests will not be able to develop resistance to the Bt toxin.

William Hutchison of the University of Minnesota, one of the lead researchers on this study, said farmers planting Bt corn should consider going to a 50/50 planting of GM and non-GM varieties. Right now, a refuge planting of only 10% of the corn crop is required to be planted. Studies by the USDA show that 25% of farmers planting Bt corn don’t plant a refuge at all.

At the same time, there are indications that demand for Bt corn from farmers has leveled off.

However, farmers have limited options when it comes to GM corn without Bt in it. Many varieties are stacked, meaning that they have more than one genetically-modified trait. If a farmer wants an herbicide-resistant corn variety or a variety with a resistance to a different pest, the trait toxic to the European corn borer is often included, whether the farmer wants it or not.

It looks like one solution could be to require the planting of a certain number of acres of non-GM corn. What do you think?

Source:Β  “Areawide Suppression of European Corn Borer with Bt Maize Reaps Savings to Non-Bt Maize Growers“, Science 8 October 2010:Β  Vol. 330. no. 6001, pp. 222 – 225
DOI: 10.1126/science.1190242 (paid site)

Image by The Marmot, used with Creative Commons license.

One comment
  1. kingofaces

    “a toxin which kills any insect that ingests it”

    That is incorrect reporting on the part of the author. Bt is a protein that targets specific groups of insects. One of the common types works on moths and butterflies (corn borer is in this group), but it doesn’t affect all them equally. Some moths and butterflies do just fine when exposed to it. Another type only works against specific beetles and does nothing to moths and butterflies. All of the types of Bt used often have no effect on other insects like lady beetles and honey bees.

    “The Bt toxin in Bt corn is so persistent, it shows up in streams near cornfields.”

    Bt is a naturally occurring toxin produced by bacteria in the soil. The study which mentions Bt in streams is fairly questionable a a few assumptions that it makes. You really can’t make the statement that the Bt levels in the streams are due to the corn specifically.

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