Assessment of resistance
evolution after intensive
use of Bt technology is
now underway
Inor Ag. Assmann
58
Resistance is needed
Integrated pest management in the Brazilian corn plantations is
focused on fighting common field problems, like armyworms
A clear grasp of what Integrated Pest Management (IPM) is all
about calls for an entirely integrated approach. This happens be-
cause the pest insects have already realized that the cultivation of
different crops is common practice in the fields, and they have
taken advantage of the situation. Researcher Simone Mendes,
from Embrapa Corn and Sorghum, stresses the importance of
a clear grasp of what the production system is integrated with,
while there are, in a succession of years, different possibilities that
compose the agricultural landscape in Brazil. It is the case of the
soybean fields that come prior to the cornfields, or the corn areas
that come prior to cotton, among others.
Currently, the armyworm (Spodoptera frugiperda), is still the
main pest in this activity, even after the liberation and large-scale
use of Br corn. “This species of insect belongs to a group of po-
lyphagous pests that feed on several plant species. “That is why
they continue infesting the fields even in the absence of corn,
feeding on plants like brachiaria grass, millet, cotton and even
soybean.” Within this scenario, the population of the worm grows
and propagates, impairing management practices, seeing that a
great number of worms exist in the area when corn is seeded.
Furthermore, Simone clarifies another phenomenon, referred
to by science as resistance evolution. After an intensive use of the
Bt technology, without the right resistance management strate-
gies, like the use of refuge areas, biotypes or strains of this species
manage to overwinter and propagate in Bt corn fields. “This resis-
tance breakage was registered in the Country initially for protein
Cry1F, present in some species available in the market. Now, we
have varied levels of susceptibility to Bt technologies, depending
on the region and the Bt species in question”, the scientist argues.
Some steps need to be taken when Bt corn is no longer effi-
cient. Initially, there is need to understand that the armyworm
possesses biotypes or strains that live in different Brazilian re-
gions. Therefore, in one region, a Bt cultivar could perform well,
but in another region, it could be the opposite. Another aspect
to be taken into consideration, and greatly important, is the cor-
rect use of the Integrated Pest Management (IPM) practice. “It is
not possible to think of managing a pest strain in the field with-
out monitoring it, in order to evaluate the level of action and the
use of diversified management strategies, like biological, cultural
and chemical control”, Simone Mendes argues.
Another major pest insect is the stink bug (Dichelops furca-
thus), common in fields where corn is grown after soybean har-
vest. The critical infestation period expires about 25 days after
seeding, when the bug sucks the sap of the plant and injects its
toxic saliva, causing leaves to wrinkle and deform in the ear-
ly development stage. In serious outbreaks, the plants remain
completely unproductive. “In this case it is equally necessary to
monitor the pest in the production system, not only in the corn
fields, where the problem of the insect reaches its peak”, the re-
searcher recommends.
