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GE - Bt crops and their impact on insects and food webs

From:           fkoechlin@datacomm.ch (Florianne Koechlin)
Subject:        mail-out 65


MAIL - OUT 65                   (March 1999)

Dear friends
This mail-out is about a newly emerging risk-discussion: Do genetically
engineered Bt-crops poison beneficial insects, bees, soil-organisms, fish,
birds? What effects do they have on food-webs, what studies have to be done
and why were they not conducted?

At an international meeting of entomologists in Basel in March 1999
scientists raised a red flag: Genetically engineered Bt-crops could poison
beneficial insects as well as wiping out pests. Angelika Hilbeck and her
team (Swiss Federal Research Station for Agroecology and Agriculture) said
they have found new evidence that lacewings, which eat caterpillars and
aphids, can be poisoned by transgenic Bt-crops (these crops contain a gene
from the soil bacterium Bacillus Thuringiensis coding for a Bt-toxin. The
transgenic plant thus produces its own insecticide). They showed already
last year that in laboratory tests beneficial lacewings were killed by
eating corn-borer caterpillars that had consumed the toxin. In other
experiments her team fed identical quantities of purified Bt-toxin directly
to lacewing larvae or via caterpillars that had consumed the toxin. 50%
more lacewings died after eating the caterpillars than after eating
directly the toxin.(N.S., 27.2.99).
At the same meeting Nicholas Birch (Scottish Crop Research Institute)
presented his findings that transgenic lectin-producing potatoes (lectin is
a toxin of the same group as the Bt-toxin) harmed ladybirds: Eating aphids
reared on transgenic lectin-potatoes reduced the the lifespans and egg
production of ladybirds.

Novartis, the producer of Bt-maize 175 (which is grown now in Spain), said
that these laboratory studies do not reflect real conditions in the
environment and pointed out that they had conducted extensive trials before
bringing their Bt-maize to the market. But Hilbeck has an explanation why
Novartis did not find any dead beneficial insects:"A standard test (..) is
that an insect is fed eggs sprayed with Bt-toxins. The problem is, however,
that lacelaws do not eat the eggs but suck them out from inside, so they do
not get in touch with the poison on the outside of the egg. Only with
long-time feeding trials and a very carefull set-up of the experiment can
such impacts be studied."(Swiss Tagesanzeiger, 19.3.99). And such
experiments have not been done.

Bt-crops are probably the most important transgenic crops: Bt-maize,
Bt-cotton, Bt-potatoes or Bt-rice grow on fields all over the world. 14 out
of 43 commercialised transgenic crops in the US are Bt-crops. Furthermore,
in the US there is a giant patent-battle going on over who will get
monopoly controll over these crops: Up to June 1998, 482 patents had been
submitted or awarded mentioning Bt, some 95 of these patents involve
transgenic plants. The top ten patentees hold 62% of all patents, with Dow
holding 98 and Novartis 36 patents. (Robin Jenkins, in 'Seedling, Sept.'98)

Industry's main-argument for the safety of Bt-crops always was the fact
that Bt-emulsions from Bt-bacterias have been used as a biological and
sprayable insecticide throughout the world since the early 1950s, and
nothing happened. However, there are 2 important differences between the
sprayable Bt-insecticide and the form of Bt engineered into the genome of
crops, as 'World Watch' (Jan./Feb.1999) points out:"First, while the
naturally derived spray version of Bt is highly specific (its toxidity is
activated only in the gut of certain species), the genetically modified
version has been altered to work against an array of insects - harmful or
not. The recent studies showed that beneficial insects were also harmed by
Bt (...) The result was a 2-fold increase in adult mortality and
reproductive failure in 2 very different beneficial species. The studies
also showed dramatically reduced fitness and increased mortality in the
beneficial larvae and eggs (..). These side-effects of Bt crops have now
been demonstrated for a wide variety of insects and soil organisms, and
preliminary studies suggest that the adverse effects could even be felt by
insect-eating bird populations, many levels up the farm foodweb - a foodweb
that includes plants and animals consumed by humans.
The second significant difference is that Bt-crops deliver extremely high
levels of the toxin - roughly 10 to 20 times the lethal dose of sprayable
formulations. Mark Whalon (Michigan State University) notes, that in
contrast to the carefully timed applications of sprayable Bt and the
"micrograms" sprayed each time (...) "these transgenic crops are now
pumping out huge amounts of toxins from all tissues throughout the entire
growing season, from germination to senescence."
The scientists also warn that the more aggressive the measures for pest
eradication, the greater the likelyhood that successive generations of
pests become more resistant. The long-term results would be a mutual arms
race between farmers and pests, in which plants engineered to secrete
increasingly toxic chemicals would be deployed against increasingly
resistant strains of pests. This heighened threat of Bt-resistence, coupled
with the devastation of beneficial insect populations that help keep pests
in check, could lead to massive crop losses.
Although initial large scale plantings of Bt-crops may appear benign, it
will likely take several seasons for toxidity and resistence problems to
emerge. (..) The scientists advocate a moratorium on large scale releases
of Bt-crops until the long-term ecological effects are better assessed".

All the best  Florianne Koechlin


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