Abstract
Simple SummaryThe Cry1Ab toxin content in different plant organs is highly variable by genetic events and cultivars. This applies particularly to the pollen, which is the main route of exposure of protected lepidopteran larvae. Thus, uncertainties appear regarding safety assessments on the basis of analytical and biological studies: (a) genetic events and cultivars produce various Cry1Ab toxin contents; thus, risk analyses based on single pollen counts may be erroneous; (b) analytical problems have been identified explaining the high variability of the documented pollen toxin content; (c) stinging nettle patches subject to maize pollen sedimentation are frequent nearby maize field edges, where protected nymphalid larvae may feed; (d) substantial maize pollen sedimentation (300–600 pollen grains/cm2 in the dominant wind direction) occurs on the leaves of stinging nettle; (e) July and August are the critical months for the young larvae of Nymphalis io, which are the most sensitive for pollen containing Cry1Ab toxin; (f) the exposure of these larvae to maize pollen containing >100 ng of Cry1Ab toxin/g results in <40% mortality and extended developmental times in younger stages. This is a definite hazard, which is a sufficient legal ground for habitat conservation of this protected species in Hungary.A credible risk analysis of maize pollen containing Cry1Ab toxin must include the assessment of (i) pollen production and its Cry1 toxin content; (ii) distribution of the pollen grains in the surroundings; (iii) pollen-catching capacity of the weeds on field edges; (iv) the lifestyle of protected lepidopteran larvae living on weeds; (v) Cry1 toxin sensitivity of non-target caterpillars; and (vi) Cry1 toxin resistance of individual non-target populations. The concentration range of 5–4300 ng Cry1Ab toxin/g dry pollen determined in MON 810 pollen batches is too diverse for handling it as a single set in any mathematical modeling. Within the work carried out mainly with the DK-440 BTY cultivar, the seed samples officially received from the variety owner produced significantly different (250–470 vs. 5–15 ng/g) Cry1Ab toxin concentrations in the pollen. Nymphalis io L1-L3 larvae were nearly six times more sensitive for Dipel than Nymphalis c-album. Feeding on the back side and in a leaf nest, Vanessa atalanta may be subject to lower pollen exposures. N. io larvae may actively attempt to avoid patches with high pollen contamination. Cry1Ab toxin resistance also partially emerged in N. io populations reared in the Pannonian Biogeographical Region (Hungary).
Highlights
Pollen containing Cry1Ab toxin ingested by non-target lepidopteran larvae that consume weeds emerging in maize fields has received wide attention by conservation biologists.Danaus plexippus larvae, reared on Asclepias syriaca leaves dusted with the pollen of “Bt maize” (N4640 maize, SYN-BT11-1—Cry1Ab), reduced their feeding activity, showed delayed growth, and suffered higher mortality than larvae reared on leaves dusted with maize pollen without Cry1Ab toxin [1]
Several commentaries [2–5] followed this pioneering paper, emphasizing that the toxicity observed is a more complex phenomenon than thought earlier, due to the interplay among various factors, including natural maize pollen distribution, Cry/Vip toxin content of different genetic events of maize and cultivars, species sensitivity to Cry/Vip toxin, and the conservation status of lepidopteran species living in Europe
The N. io larvae actively avoid feeding on leaf patches with pollen densities over 1000 pollen grains/cm2, and for this reason, dose-dependence does not exist in the case of maize pollen with Cry1Ab toxin content
Summary
Pollen containing Cry1Ab toxin ingested by non-target lepidopteran larvae that consume weeds emerging in maize fields has received wide attention by conservation biologists. There has been an ongoing formal debate on non-target environmental effects, resulting in several national moratoria Economic reasons, such as the technology fee for patents, the contract system restricting farmers’ rights, concerns regarding the narrowing of national variety choices, practical problems of field treatment and consumer aversion all play roles in rendering MON 810 the only genetic event in the EU approved for public cultivation. Spain and Portugal have authorized and cultivated MON 810 maize cultivars in practically important field sizes. It reached ~30% of maize production in Spain during 2010–2015. Contaminated with sedimented MON 810 pollen (sketch) Notes: + increases the risk; – decreases the risk
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