Bt corn ravages (some) farmer profits

Is it possible that corn (maize) farmers in the US eastern corn belt are collectively giving up on $99 million a year ($1.98 billion in lifetime benefits) by paying too much for seed? That seems to be one possible conclusion of a paper just published in Science.

A large team led by Christian Krupke at Purdue University looked in detail at university field trials of corn engineered to resist corn rootworm, the larva of a beetle that can cause severe damage and yield loss by munching on the plant’s roots. Since 2003, GMO corn has been available that produces toxins derived from a bacterium, Bacillus thuringiensis, that kill rootworms and protect yield. Widespread planting of Bt corn followed, with two opposite effects.

By killing off the larvae, Bt corn reduces the number of adults that are present the following year, reducing damage by suppressing pest numbers. However, Bt corn also selects for larvae resistant to the toxins, increasing the likelihood of further damage. In some places and some crops, pest suppression has been a success; widespread use of Bt cotton contributed to the eradication of the pink bollworm. But increasing resistance means that seed companies have needed to engineer ever more Bt toxins into their varieties to maintain the same level of protection.

In the US, the Environmental Protection Agency mandated so-called refuges; a certain proportion of the farmer’s field had to be planted with non-Bt corn so that susceptible pests survived. The idea was to combat the potential tragedy of a mismanaged commons, where an individual farmer’s decision to plant all of their land with Bt corn would cause more resistance, the costs of which would be borne by their neighbours. The optimum decision for how much Bt corn to plant would be higher than the optimum for the community as a whole. It could be, though, that widespread pest suppression might be a good thing for all concerned, as it was for cotton farmers and the pink bollworm. In that case the individual optimum and the group optimum would be similar.

The researchers looked at rootworm damage and yields from a series of trials conducted by universities across the corn belt comparing Bt and non-Bt plots. They were able to separate the effects of pest suppression and resistance by looking at the past history of each field.

Root injury was highest in plots planted with non-Bt corn, as expected. In non-Bt plots, a history of Bt corn reduced root damage, showing the benefit of pest suppression. The best protection was seen for Bt maize in plots that had no Bt history, again as expected. The key finding was lower protection if there had been Bt corn in the plot before, showing that the effects of selection outweighed the benefits of pest suppression.

That’s the background to the really interesting part of the paper, a cost-benefit analysis of the consequences. For this, the researchers compared western corn belt states (ND, SD, NE, MN, IA, WI, IL) with eastern states (IN, MI, OH). There are two big differences. In western states, corn is often grown continuously year after year in the same fields, while in eastern states corn is usually grown in rotation with other crops. As a result, more rootworms are present in western states, where they cause around six times more damage than in eastern states.

In both regions, farmers pay a premium of around $25 per acre for Bt seed and in both regions rates of BT planting are roughly the same, 59% in the west and 50% in the east. In the west, that rate is very close to the calculated group optimum. In the east, however, farmers are planting far more Bt corn than they “ought” to, calculated as between 12% and 20%. And the cost of that?

“Farmers could have accrued one-year benefits of 99.0 million USD and lifetime benefits of 1.98 billion USD simply by reducing the Bt planting rate from 50 to 18%”

Why don’t they? Several possible reasons. It seems unlikely that eastern corn farmers simply don’t recognise the costs of protecting against corn rootworm. More likely, consolidation in the seed industry along with industry’s bundling of a package of engineered traits means that they simply cannot get only the traits they need. If they want drought or flooding tolerance, or herbicide resistance, those traits are often available only with a whole bunch of other traits that the farmers don’t need, and as a result of the bundling they don’t even know how much those unnecessary traits are costing them. Bundled traits also run the risk of selecting for resistance in pests that currently do not do much damage.

The researchers say they would like to see government pressure on seed companies to offer greater diversity and to indicate separately the price premium for each bundled trait. That seems unlikely, especially now. For the farmers, I reckon that the ideal individual strategy for an eastern corn farmer now is to abandon Bt corn and take advantage of all your neighbours who are paying to suppress the pest popluation even though they don’t need to.