London (11.1.10)
– Almost as soon as the idea of genetically modified Bt-(insect-resistant)
was first proposed, concern was expressed by some people that insects other
than the target species that attack the plant crop in question would be adversely
affected. Never mind that many wild plants resist insect attack by virtue
of their endogenous insecticide; never mind either than under pressure from
insect attack there will be some spontaneous development of resistance by
plants. Or, indeed, that spraying plants externally with insecticides is random
in its effect, hitting target as well as non-target insects. It was only crop
plants deliberately made insect-resistant by the insertion of a gene coding
for a protein innocuous to other animals that the objections were raised by
pressure groups.
The question was what happened in practice with GM Bt-plants. It was already
known from a series of papers some years ago that Monarch butterflies caterpillars
feeding on milkweed in the neighbourhood of Bt-maize, and hence possibly exposed
to some Bt-maize pollen, were not wiped out as the activists had claimed they
would be (1, 2).
A new study (3) has generated a mathematical model to explore the risk of
exposure. They started from genetically modified (GM) maize MON810 which expresses
a Cry1Ab insecticidal protein, derived from Bacillus thuringiensis
(Bt), toxic to lepidopteran target pests such as Ostrinia nubilalis,
the European Corn Borer. An environmental risk to non-target Lepidoptera from
this GM crop is exposure to harmful amounts of Bt-containing pollen deposited
on host plants in or near MON810 fields. An 11-parameter mathematical model
analysed exposure of larvae of three non-target species: the butterflies Inachis
io (L.) and Vanessa atalanta (L.), and the moth Plutella xylostella
(L.), in 11 representative maize cultivation regions in four European countries.
A mortality–dose relationship was integrated with a dose–distance
relationship to estimate mortality both within the maize MON810 crop and within
the field margin at varying distances from the crop edge. Mortality estimates
were adjusted to allow for physical effects; the lack of temporal coincidence
between the susceptible larval stage concerned and the period over which maize
MON810 pollen is shed; and seven further parameters concerned with maize agronomy
and host-plant ecology. Sublethal effects were estimated and allowance made
for aggregated pollen deposition.
The estimated environmental impact was low: in all regions, the calculated
mortality rate for worst-case scenarios was less than one individual in every
1572 for the butterflies and one in 392 for the moth.
Sources:
1. http://www.cropgen.org/answer21.html
2. A.M.R.Gatehouse, N. Ferry, and R.J.M. Raemaekers (2002). The case of
the monarch butterfly: a verdict is returned. Trends in Genetics, 18,
249-251.
3. J. N. Perry, Y. Devos, S. Arpaia, D. Bartsch, A. Gathmann, R. S. Hails,
J. Kiss, K. Lheureux, B. Manachini, S. Mestdagh, G. Neemann, F. Ortego, J.
Schiemann and J. B. Sweet (6.1.10). A mathematical model of exposure of
non-target Lepidoptera to Bt-maize pollen expressing Cry1Ab within Europe.
Proceedings Of The Royal Society B (http://rspb.royalsocietypublishing.org/content/early/2010/01/05/rspb.2009.2091.full.pdf+html)
<<<back
