Badania z 2001 roku. Te badania są już dokładniejsze niż te z 1999 roku. Uczeni stwierdzili, że zmodyfikowane genetycznie białko Bt jest niewątpliwie toksyczne dla motyli (i nie tylko motyli). Białko to ulega ekspresji w pyłku. Toksyczność pyłku jest uzależniona od stopnia stężenia Bt w pyłku. Brano też pod uwagę możliwość wystąpienia innych czynników, takich jak pestycydy. Ostatecznie stwierdzono, że Bt zawarte w pyłku jest niewątpliwie toksyczne dla motyli. Uznano, że toksyczny wpływ modyfikowanej kukurydzy na populację Monarchy jest nieznaczny, ale zaznaczono, i to jest tutaj najistotniejsze, że uczeni biorący udział w tym badaniu nie są w stanie stwierdzić, jakie mogą być dalekosiężne, przewlekłe, skutki notorycznego zatruwania populacji Monarchów modyfikowanym genetycznie białkiem Bt.
„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.
Concern regarding nontarget effects of transgenic crops containing transgenes from the organism Bacillus thuringiensis (Bt) arose after the publication by Losey et al.(1) on the potential risk of corn pollen expressing lepidopteran-active Cry protein to the monarch butterfly, Danaus plexippus L. However, the U.S. Environmental Protection Agency (EPA) concluded in an earlier report that the potential impact of Bt corn pollen, which contains variable amounts of Cry protein, on sensitive larvae of Lepidoptera was negligible because of factors that limit environmental exposure (2). Clarification of the risk posed by Bt corn pollen to monarch butterflies can now be undertaken because of the data reported in this issue of PNAS (3–6) that address exposure and toxic effects of Bt corn pollen.
Only three papers concerning the impact of Bt corn pollen on nontarget Lepidoptera have been published (1, 8, 9), and they are limited in their application to risk assessment (7).
In this paper, we develop a weight-of-evidence approach to the risk of exposure of monarch larvae to Bt corn pollen and the impact of such exposure on populations of the monarch butterfly in eastern North America by using recently published information based on collaborative research by scientists in the U.S. and Canada (3–6). We use an approach to risk assessment that has been performed for many nontarget species in relation to pesticides (10–14), industrial by-products (15, 16), and other potential toxicants found in the environment (17). The approach to this process is consistent, well documented, and standardized (www.epa.gov/NCEA/ecorsk.htm). It requires consideration of both the expression of toxicity and the likelihood of exposure to the toxicant as the basic components for a risk assessment procedure.”