Agriculture Reference
In-Depth Information
h ere are also other factors that can lead
to changes in Bt ef ects over time. In China,
for instance, insecticide applications some-
what increased again after several years of
Bt cotton use, in spite of the absence of Bt
resistance. Wang
et al
. (2008) attributed
this to secondary pests, which might have
become more important through the
Bt-induced reduction in broad-spectrum
insecticides. Secondary pests are mirids,
mealybugs and other sucking pests that are
not controlled by Bt. Using long-term i eld
trial data from China, Lu
et al
. (2010) also
found that secondary pest populations
increased in Bt cotton. Krishna and Qaim
(2012) analysed pesticide use patterns in
India over a period of 7 years. h ey found
that farmers with Bt cotton increased their
sprays against sucking pests. Nevertheless,
pesticide reductions through Bt increased
over time, because the rise in sprays against
secondary pests was more than of set by the
decline in sprays against bollworms.
Krishna and Qaim (2012) found that
conventional cotton growers in India could
reduce their sprays as well, because the
widespread adoption of Bt cotton led to
area-wide suppression of bollworm
populations. Similar ef ects were reported
for Bt cotton in China and Bt maize in the
USA (Wu
et al
., 2008; Hutchison
et al
.,
2010).
Bt crops are also associated with health
benei ts. Direct health advantages for
farmers occur due to less insecticide
exposure during spraying operations. Often,
the health hazards for farmers applying
pesticides are greater in developing than
developed countries, because environmental
and health regulations are laxer, pesticides
are mostly applied manually and farmers are
less educated and less informed about
negative side ef ects. Pray
et al
. (2001) and
Huang
et al
. (2003) showed for China that
the frequency of pesticide poisonings was
signii cantly lower among Bt cotton adopters
than non-adopters. Hossain
et al
. (2004)
used econometric models to establish that
this observation was related causally to Bt
technology. Bennett
et al
. (2003) and Kouser
and Qaim (2011) obtained similar results
for Bt cotton in South Africa and India.
For consumers, Bt crops can bring about
health benei ts through lower pesticide
residues in food and water. Furthermore, in
a variety of i eld studies, Bt maize has been
shown to contain signii cantly lower levels
of certain mycotoxins, which can cause
cancer and other diseases in humans (Wu,
2006). Especially in maize, insect damage is
one factor that contributes signii cantly to
mycotoxin contamination (see Table 6.1). In
the USA and other developed countries,
maize is inspected carefully so that lower
mycotoxin levels primarily might reduce the
costs of testing and grading. But in many
developing countries, strict mycotoxin
inspections are uncommon. In such
situations, Bt technology could contribute
to lowering the actual health burden (Wu,
2006; Parrott, 2010).
h e studies discussed so far build on micro-
level data collected through farm surveys
and i eld observations. But GM crops are
now grown on 170 Mha worldwide, so
impacts are also observable at the macro
level. Sexton and Zilberman (2012) tried to
evaluate these macro-level ef ects. Based on
several years of data, they estimated cross-
country regressions, where the production
quantities of dif erent agricultural crops in a
country were explained by land area and
area grown with GM crops. In all regressions,
the GM crop area has large and signii cant
positive ef ects, implying that GM tech-
nology adoption has increased country-level
agricultural output. For GM soybean, the
average production-increasing ef ect in
technology-adopting countries was 13%, for
GM rapeseed it was 25% and for GM maize
and cotton it was 46% and 65%, respectively
(Sexton and Zilberman, 2012). Not all of
these increases are net yield gains of GM
technology. Technology-adopting farmers
may also have increased their fertilizer
applications. In some cases, better weed
control with GM allows farmers to grow a
second crop per year, as is observed partly
for HT soybeans in South America. But GM
technology has triggered these ef ects, so
