Monarchs and the Bt Transgenic Corn Pollen Scare

[Cris Guppy & Aud Fischer]

In reference to monarch larva mortality to ingesting "Bt corn pollen". Paul
Cherubini does not know the full story about Btk, and has not fully
considered the significance of increased monarch mortality. First, Btk does
NOT harmlessly disappear within a week or so of application. Scriber et al
(1995) "Swallowtail Butterflies: Their Ecology & Evolutionary Biology"
(Scientific Publishers, page 326) describes an experiment replicated over
two summers which show that leaves sprayed with Btk under normal field
conditions resulted in 100% mortality to swallowtail larvae placed on the
leaves 30 days after the spraying. Larvae on unsprayed control leaves in the
field had only about 30% mortality. So the effects of Btk spray can last
over a month. There is very little literature on the effects of Btk on
non-target Lepidoptera, because neither government nor industry is
interested in funding potentially "bad news" research. Second, if my memory
is correct a large proportion of milkweed in much of the corn belt states
grows on road shoulders adjacent to corn fields, because a large proportion
of the rest of the states are corn fields (a local resident of the corn belt
can confirm or refute that). And road shoulders tend to be within 20 feet of
cornfields, not 200 feet, allowing ample opportunity for pollen to load onto
road shoulder milkweeds. So potentially a large proportion of monarch larvae
may be affected. Third, even a 5% density independant mortality factor can
be very significant to a population. Populations of monarchs are already
declining as the result of various human mortality factors at all stages of
the life history, so is not an additional 5% mortality of great concern? And
apparently the Bt gene has been added to aspen being planted in nothern
Alberta. Aspen has an incredible output of pollen that covers everything in
the forest. Shall we have entire aspen forests raining Bt-laden pollen on
every lepidopteran foodplant within it?