The maize field ecosystem
Within the EU, Bt maize has to date been cultivated on an appreciable scale only in Spain. Other EU countries, beneath Germany and France, has voiced a national veto for cultivating Bt maize. Genetically modified Bt maize produces a substance to protect it from its antagonist, the European corn borer .
If large-scale cultivation of genetically modified crops is introduced in Europe, this will primarily involve Bt maize.
A large number of safety research projects have focused on Bt maize, mainly on possible effects on the maize agro-ecosystem, by looking at a large number of non‑target organisms .
Projects completed in 2005-2008 focused on Bt maize resistant to the Western corn rootworm (Diabrotica v.virgifera), a beetle. This maize is not licensed for cultivation in the EU, but in recent years the pest has been spreading steadily across Europe, reaching Germany for the first time in 2007.
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Research projects: results summaryTopic: A large number of small creatures and micro-organisms live in the maize field. They form a species community and each has a place in the food chain. These organisms come into contact with the Bt toxin either directly by eating the plant, or indirectly, by eating or parasitizing prey that have eaten Bt pollen or Bt plant parts. Result (1): Varietal differences were found among the insects in the herbaceous layer and among the pollen feeders and flower visitors, but no Bt effect was found. Fluctuations were attributed to differences in soil and weather conditions. There were also fluctuations from year to year. Result (2): Analyses give no indication that Bt maize has any effect on the frequency and species diversity of non-target organisms. However, the sprayed insecticide was found to have a clear effect on some insect groups. Result (3): The choice of maize variety (Bt maize or a conventional, isogenic reference variety) had no discernible effect on the abundance of arthropods, aphids or their antagonists. Result (4): Varietal differences were found among the insects in the herbaceous layer and among the pollen feeders and flower visitors, but no Bt effect was found. Fluctuations were attributed to differences in soil and weather conditions. There were also fluctuations from year to year. Result (5): So far the cultivation of Bt maize has been shown to have no negative effects on beneficial insects (aphids, cicadas, parasitic wasps, lacewings, hover fly larvae and eggs, ladybirds, predatory bugs and spiders)
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Result (6) Leaf beetles: Leaf beetles are related to the Western corn rootworm, which is targeted by the Bt maize variety being studied in this project (MON 88017). Young larval stages in particular of three of the leaf beetle species studied were found to be sensitive to pure Cry3Bb1 protein on their food plants. The mortality rate was higher; weight gain and pupation rates were lower. By contrast, when maize pollen was fed to two species of leaf beetle larvae, no negative effects on larval mortality, weight gain or pupation rate were observed. Acute damage to the species investigated is unlikely under field conditions, since the amount of toxin ingested via the pollen is probably a lot less than the calculated LD50 dose. Neither were any indications of possible chronic toxicity
or sublethal damage found as a result of ingesting pollen from MON88017 maize.
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Result (7) Spiders: Laboratory: The consumption of Bt toxin, Bt maize pollen and/or bees which have foraged in Bt maize had no negative effect on the mortality rate, lifespan, weight gain, reaction to prey or web parameters of three species of orb-weaver (mangora acalypha, garden cross spider and wasp spider). Field: The spider population in 2001 was significantly lower in the Bt field than in the control fields; in 2002 there was no difference and in 2003 it was higher. The direction of the effects appears to be governed by other (environmental) factors. Result (8) Spiders: Laboratory and field studies show that the brown comb-footed spider absorbs Bt toxin through its prey. Lower concentrations (than in their prey) indicate that the toxin is broken down and eliminated and does not accumulate in the spider. Preliminary laboratory trials with prey fed on Bt maize showed no negative effects on survival or reproduction of the spiders.
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Result (9) Aphids: Laboratory: Research into the developmental stages of aphids: No differences were found between the individual maize variants. Tent trials: The transgenic maize strains were not found to have any effect on the parasitization activity of the parasitoids (parasitic wasps as aphid antagonists) in the tent trial. Nor was any impact detected on the composition of parasitic wasp populations. Field: The transgenic maize varieties studied were not found to have any effect on the population development of the aphids, but varietal differences were found. Result (10) Parasitic wasps: Trichogramma parasitic wasps are natural antagonists of the European corn borer and so are also used as a means of control. Feeding trials: Research into the toxic effects of various Bt maize plant parts on Trichogramma showed no significant negative effects on parasitization or life span. Field trials were not carried out because the laboratory experiments showed no significant effects.
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Result (11) Bees: Laboratory: Feeding bees with pollen containing up to 100 times the concentration of the toxin found in Bt maize pollen produced no effects. Feeding experiments with larvae did not produce any effects either. Field: In tent-like enclosures, bee colonies were fed Bt maize pollen with up to 10 times the normal toxin concentration. No negative effects were observed. There were no differences in the number of bees, foraging and brood care activity or hatching weight compared with bee colonies fed on non-Bt maize pollen. A chance parasitic infestation (microsporidia) caused more significant damage to the Bt-fed colonies. The mechanism behind this was not discovered. |
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