Pollen From Genetically-Manipulated Crops Harms Monarch Butterfly Larvae
Monsanto Investing News web page.
Transgenic pollen harms monarch larvae
Excerpts from Scientific Journal, Nature, Volume 214, 1999
Although plants transformed with genetic material from the bacterium
Bacillus thuringiensis (Bt) are generally thought to have negligible impact
on non-target organisms1, Bt corn plants might represent a risk because
most hybrids express the Bt toxin in pollen2, and corn pollen is dispersed
over at least 60 metres by wind3. Corn pollen is deposited on other plants
near corn fields and can be ingested by the non-target organisms that
consume these plants. In a laboratory assay we found that larvae of the
monarch butterfly, Danaus plexippus, reared on milkweed leaves dusted with
pollen from Bt corn, ate less, grew more slowly and suffered higher
mortality than larvae reared on leaves dusted with untransformed corn
pollen or on leaves without pollen.
Larval survival (56%) after four days of feeding on leaves dusted with Bt
pollen was significantly lower than survival either on leaves dusted with
untransformed pollen or on control leaves with no pollen (both 100%,
P=0.008) (Fig. 1a). Because there was no mortality on leaves dusted with
untransformed pollen, all of the mortality on leaves dusted with Bt pollen
seems to be due to the effects of the Bt toxin.
These results have potentially profound implications for the conservation
of monarch butterflies. Monarch larvae feed exclusively on milkweed
leaves4; the common milkweed, A. syriaca, is the primary host plant of
monarch butterflies in the northern United States and southern Canada5.
Milkweed frequently occurs in and around the edges of corn fields, where it
is fed on by monarch larvae6. Corn fields shed pollen for 8-10 days between
late June and mid-August, which is during the time when monarch larvae are
feeding7. Although the northern range of monarchs is vast, 50% of the
summer monarch population is concentrated within the midwestern United
States, a region referred to as the 'corn belt' because of the intensity of
field corn production8. The large land area covered by corn in this region
suggests that a substantial portion of available milkweeds may be within
range of corn pollen deposition.
With the amount of Bt corn planted in the United States projected to
increase markedly over the next few years9, it is imperative that we gather
the data necessary to evaluate the risks associated with this new
agrotechnology and to compare these risks with those posed by pesticides
and other pest-control tactics.
John E. Losey, Linda S. Rayor, Maureen E. Carter
Department of Entomology, Comstock Hall, Cornell University, Ithaca, New York