Bt corn susceptible to both rootworms and aphids (22/7/2007)

1.The root of the issue: Corn yields surprises
2.High Susceptibility of Bt Maize to Aphids

NOTE: The reporting of research showing problems with Bt corn (maize) is given a decidedly positive spin in both these items. Yes, Bt corn seriously fails to protect against rootworms despite farmers paying Monsanto big bucks for that protection (item 1), but heck it does a great job against corn borers! Likewise, when Bt corn turns out to be significantly more susceptible to aphid infestation (item 2), this can be construed as a "remarkable positive effect" on the "performance" of the corn leaf aphid! Thus, the panglossian researcher moves safely though biotech's best of all possible worlds.


1.The root of the issue: Corn yields surprises
Anne Cook The News-Gazette, July 13 2007 [shortened]

URBANA The stacked corn traits farmers pay big bucks for aren't keeping rootworms from munching on their favorite food.

[University of Illinois entomologists Mike Gray and Kevin Steffey] and their student assistants this week started digging up corn plants in UI fields to look at their root system health, an annual ritual for these scientists who study pests that prey on the state's largest crop.

Gray said they've discovered some surprising differences in their 25-acre test plots near South Race Street. He said project overseer Ron Estes called their attention to the surprising difference in height between one transgenic variety that contains proteins engineered to kill both corn borers and rootworms, and its close relative without the traits.

The second surprise is that rootworms did significant early damage to transgenic varieties.

Gray said they started digging up roots to evaluate damage in July as well as August for a very specific reason a severe storm that swept through in July a few years ago and flattened a lot of corn fields, a sure sign rootworms have been at work in the ground.

"There was more damage than expected," he said. "That was an opportunity presented to us. We decided to do a second set of evaluations to compare roots treated with soil insecticide to roots of transgenic varieties with stacked traits for rootworm and corn borer protection."

Technology incorporated into plants to make them lethal to insects relies on Bacillus thuringiensis, a bacterium that expresses a protein that breaks down the digestive system of insects when they ingest it.

But Steffey said the technology introduced in 1996 that works so well for corn borers, killing about 99 percent of the beetles that eat it, doesn't work as well on rootworms, technology introduced in 2003.

"You don't get the expression in the roots that you get in the leaves," he said, adding that many companies don't emphasize that fact when they're selling their stacked hybrids to farmers.


2.High Susceptibility of Bt Maize to Aphids Enhances the Performance of Parasitoids of Lepidopteran Pests

Concerns about possible undesired environmental effects of transgenic crops have prompted numerous evaluations of such crops. So-called Bt crops receive particular attention because they carry bacteria-derived genes coding for insecticidal proteins that might negatively affect non-target arthropods.

Here we show a remarkable positive effect of Bt maize on the performance of the corn leaf aphid Rhopalosiphum maidis, which in turn enhanced the performance of parasitic wasps that feed on aphid honeydew. Within five out of six pairs that were evaluated, transgenic maize lines were significantly more susceptible to aphids than their near-isogenic equivalents, with the remaining pair being equally susceptible.

The aphids feed from the phloem sieve element content and analyses of this sap in selected maize lines revealed marginally, but significantly higher amino acid levels in Bt maize, which might partially explain the observed increased aphid performance. Larger colony densities of aphids on Bt plants resulted in an increased production of honeydew that can be used as food by beneficial insects.

Indeed, Cotesia marginiventris, a parasitoid of lepidopteran pests, lived longer and parasitized more pest caterpillars in the presence of aphid-infested Bt maize than in the presence of aphid-infested isogenic maize. Hence, depending on aphid pest thresholds, the observed increased susceptibility of Bt maize to aphids may be either a welcome or an undesirable side effect.

Authors: Cristina A. Faria, Felix L. Wäckers, Jeremy Pritchard, David A. Barrett, Ted C.J. Turlings

To read the original journal article (as a pdf), here http://www.plosone.org/article/fetchObjectAttachment.action?representation=PDF&uri=info%3Adoi%2F10.1371%2Fjournal.pone.0000600

(This journal article was originally published in PLoS. Open Access.)

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