Article

Impact of Bt corn pollen on monarch butterfly populations: a risk assessment. Proc Natl Acad Sci U S A

Department of Environmental Biology, University of Guelph, Guelph, ON, Canada N1G 2W1.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 11/2001; 98(21):11937-42. DOI: 10.1073/pnas.211329998
Source: PubMed

ABSTRACT

A collaborative research effort by scientists in several states and in Canada has produced information to develop a formal risk assessment of the impact of Bt corn on monarch butterfly (Danaus plexippus) populations. Information was sought on the acute toxic effects of Bt corn pollen and the degree to which monarch larvae would be exposed to toxic amounts of Bt pollen on its host plant, the common milkweed, Asclepias syriaca, found in and around cornfields. Expression of Cry proteins, the active toxicant found in Bt corn tissues, differed among hybrids, and especially so in the concentrations found in pollen of different events. In most commercial hybrids, Bt expression in pollen is low, and laboratory and field studies show no acute toxic effects at any pollen density that would be encountered in the field. Other factors mitigating exposure of larvae include the variable and limited overlap between pollen shed and larval activity periods, the fact that only a portion of the monarch population utilizes milkweed stands in and near cornfields, and the current adoption rate of Bt corn at 19% of North American corn-growing areas. This 2-year study suggests that the impact of Bt corn pollen from current commercial hybrids on monarch butterfly populations is negligible.

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Available from: Blair D Siegfried, Mar 14, 2014
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    • "The timing of when maize pollen is shed and when the most sensitive life stages are foraging (generally neonates and early instars) may not overlap, which limits exposure. Pollen deposition rates, Cry protein stability in pollen, host plant density, cropping area, temporal and spatial overlap, and larvae feeding behavior are all important considerations that mitigate the magnitude and duration of exposure of pollinators and pollen feeders to Cry proteins in maize pollen (Sears et al., 2001). Hazard studies on honeybee (Apis mellifera) (Maggi, 1999) and monarch butterfly (Danaus plexippus) (Bystrak, 2000) demonstrate low hazard of the Cry1F protein at concentrations that exceed realistic environmental concentrations. "
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    ABSTRACT: Maize (Zea mays) is a widely cultivated cereal that has been safely consumed by humans and animals for centuries. Transgenic or genetically engineered insect-resistant and herbicide tolerant maize, are commercially grown on a broad scale. Event TC1507 (OECD unique identifier: DAS-Ø15Ø 7-1) or the Herculex® (‡) Herculex Insect Protection technology by Dow AgroSciences and Pioneer Hi-Bred. Herculex is a registered trademark of Dow AgroSciences LLC. (Herculex logo here) I trait, an insect-resistant and herbicide-tolerant maize expressing Cry1F and PAT proteins, has been registered for commercial cultivation in the US since 2001. A science-based safety assessment was conducted on TC1507 prior to commercialization. The safety assessment addressed allergenicity; acute oral toxicity; subchronic toxicity; substantial equivalence with conventional comparators, as well as environmental impact. Results from biochemical, physicochemical, and in silico investigations supported the conclusion that Cry1F and PAT proteins are unlikely to be either allergenic or toxic to humans. Also, findings from toxicological and animal feeding studies supported that maize with TC1507 is as safe and nutritious as conventional maize. Maize with TC1507 is not expected to behave differently than conventional maize in terms of its potential for invasiveness, gene flow to wild and weedy relatives, or impact on non-target organisms. These safety conclusions regarding TC1507 were acknowledged by over 20 regulatory agencies including United States Environment Protection Agency (US EPA), US Department of Agriculture (USDA), Canadian Food Inspection Agency (CFIA), and European Food Safety Authority (EFSA) before authorizing cultivation and/or food and feed uses. A comprehensive review of the safety studies on TC1507, as well as some benefits, are presented here to serve as a reference for regulatory agencies and decision makers in other countries where authorization of TC1507 is or will be pursued.
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    • "Research has established potential impacts on many terrestrial organisms, including monarch butterfly (Danaus plexippus) populations (Losey et al. 1999; Sears et al. 2001; Kaplan 2002; Dively et al. 2004), soil bacteria (Baumgarte & Tebbe 2005), slugs (Hönemann & Nentwig 2010), ladybirds (Schmidt et al. 2009), common green lacewings (Chrysoperla carnea) (Hilbeck 2001), earthworms (Zwahlen et al. 2003), and land snails (Kramarz et al. 2009). Although knowledge on Bt toxin impacts on terrestrial ecosystems has been assessed (Barton & Dracup 2000; Conner et al. 2003; Rose and Diverly 2007), there is uncertainty regarding the impacts of Bt corn detritus on stream ecosystems. "
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    • "Studies of entomofaunistic diversity in agroecosystem are rare (Pérez et al. 2011). There are studies on how insect diversity behaves in transgenic crops with pest insects (Betz et al. 2000), nontarget organisms (Naranjo 2005, Torres and Ruberson 2008, Yu et al. 2011, Comas et al. 2013, Dhillon and Sharma 2013), resistance (Wilson et al. 1992, Benedict et al. 1996) and insects without agricultural importance (Sears et al. 2001). Plants with Cry proteins are resistant to damage by certain insects (Romeis et al. 2008, Sainsbury et al. 2012). "
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