One of my colleagues pointed out to me that, in addition to the effect of
the Bt corn pollen on wild butterflies like monarchs, this also has
implications for the use of refugia in attempting to delay the development
of resistance to Bt in corn crop pests.
The point of having refugia (plantings of corn which are not Bt-transformed
or treated with Bt -- they can be treated with other insecticides, in which
case they must be much larger, or they can be treated with no insecticide at
all) is to have a supply of caterpillars of European corn borer and other
corn lepidopteran pests (e.g. corn earworm and fall armyworm) that are not
exposed to Bt and thus not under selection pressure for resistance. This
susceptible population is supposed to swamp any rare genes for resistance to
Bt. The assumption has been that these rare genes for resistance would be
recessive. That assumption was called into question by the article in
Science last week.
The assumption that these caterpillars would not be exposed to Bt in the
refugia is called into question by this new article, pointing out that the
Bt-transformation is expressed substantially in the pollen. This Bt pollen
would be all over the plants in the refugia (which are supposed to be
planted close to the Bt corn to ensure mating between the resistant and
susceptible moths). During the stages when the caterpillars are feeding out
on the plants (as opposed to tunneling within the stalk) they would be
eating this pollen along with plant material. Thus, they would be exposed
to variable doses of Bt (the very thing the high-dose strategy is supposed
to avoid). Also, corn earworms feeding in the silk might be exposed to
variable doses of Bt pollen stuck on the corn silk (and maybe in the pollen
tubes growing down the silk?) So, another assumption on which the
deployment strategy for Bt-corn was based may be wrong.
Kim Stoner
CT Agricultural Experiment Station
P.O. Box 1106
New Haven, CT 06504
203-974-8480
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