Many of the genetically modified (GM) agricultural crops cultivated worldwide are insect-resistant. These crops, including maize, contain Bt toxins which are toxic to certain pest insects. Environmental risk assessments are part of applications for the cultivation of insect-resistant GM maize lines and must include the potential adverse effects of the crop on other organisms than the pest organisms (non-target organisms), such as Lepidoptera (butterflies and moths). The caterpillars of lepidopteran species that occur in maize field margins may be exposed to Bt toxins. If any of these species are susceptible to the Bt toxin concerned, this could lead to a decline in the size of lepidopteran populations.
COGEM has commissioned a research project to investigate the occurrence of lepidopteran species in maize field margins in the Netherlands. The researchers carried out a literature study and used information on field margin vegetation and field data (distribution data of lepidopteran species) to investigate the potential occurrence in the Netherlands of lepidopteran species (butterflies and macro-moths) which are dependent for their survival on maize field margins (up to 30 m from the field).
The researchers identified 19 butterfly species and 28 macro-moth species which occur in and around maize fields and whose caterpillars may be exposed to Bt toxins via deposition of GM pollen during the flowering period of maize or by eating GM plants. However, the habitats of lepidopteran species present in the Netherlands are not restricted to maize fields and field margins. There are no species for which more than 50% of its distribution or population occur in maize fields and field margins. The researchers therefore conclude that lepidopteran species in the Netherlands do not largely (>50%) depend for their survival on maize fields and field margins, where they could potentially be exposed to Bt toxins.
Further, the study revealed that the Red List species Dusky Large Blue (Phengaris nausithous) is the butterfly species most dependent on maize field margins. There is just a single population of this species in the Netherlands. It occurs in an area where much maize is cultivated and 38% of the records of this species are from maize field margins.