NOTE: Findings in a study, published in the journal Environmental Management and Change, showing increased secondary pests since the adoption of Bt cotton in China, back up previous studies showing an explosion in secondary pests following the use of Bt cotton.

For instance, in May 2010 the journal Nature reported under the headline "GM crop use makes minor pests major problem" that, "Numbers of mirid bugs (insects of the Miridae family), previously only minor pests in northern China, have increased 12-fold since 1997, [the researchers] found. 'Mirids are now a main pest in the region,' says Wu. 'Their rise in abundance is associated with the scale of Bt cotton cultivation.'"
http://www.nature.com/news/2010/100513/full/news.2010.242.html

Mirids can reduce cotton yields just as much as the bollworms Bt cotton is designed to resist, and the paper, originally published in the journal Science, also noted that the resulting mirid infestations weren't only affecting Bt cotton but were spreading out to threaten other crops such as green beans, cereals, vegetables and various fruits. (Mirid Bug Outbreaks in Multiple Crops Correlated with Wide-Scale Adoption of Bt Cotton in China)
http://www.sciencemag.org/content/328/5982/1151

This backed up the findings of a paper published in 2008 in the International Journal of Biotechnology, which also drew on field data collected in China. This indicated that the apparent financial benefits of Bt cotton had been more or less completely eroded by the increasing use of pesticides by Bt farmers in their battle to control secondary pests.
http://www.inderscience.com/offer.php?id=18348

In a presentation prepared for the American Agricultural Economics Association Annual Meeting at Long Beach, California, the authors noted that Bt farmers were having to use these increasingly heavy volumes of pesticides to try and control pests rarely seen in the field prior to the adoption of Bt cotton.
http://www.grain.org/btcotton/?id=374
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Benefits of Bt Cotton Elude Farmers in China Over Time
Publication date: April 22, 2011
http://www.biosafety-info.net/article.php?aid=778

THIRD WORLD NETWORK BIOSAFETY INFORMATION SERVICE
 
Dear Friends and colleagues,
 
RE: Benefits of Bt Cotton Elude Farmers in China Over Time
 
According to a study published in the journal Environmental Management and Change, a substantial number of farmers in three-cotton producing regions in China have reported that secondary pests have increased since they adopted the use of Bt cotton which is genetically engineered to resist pests such as the bollworm. This is consistent with the scientific literature, which posits that secondary pests are likely to increase over time.                           
The study also found that the reduction of pesticides use has been lower than reported elsewhere, suggesting that more pesticides are needed to combat emerging secondary pests. Thus, the benefit of growing Bt cotton to reduce pesticides use diminishes in the longer term.

The study also debunks the myth that Bt cotton produces higher yields compared to conventional cotton. About a quarter of the farmers reported a lower productivity of Bt cotton versus conventional varieties. In addition, about 60% of the farmers surveyed found that overall production costs have not decreased due to higher prices of Bt cotton seed.
 
The research is based on a study of 1000 randomly selected farm households in five provinces in China. The full paper is available (for free) at: http://www.springerlink.com/content/rj34j3v323423086/

With best wishes
Third World Network
...
Benefits of Bt cotton counterbalanced by secondary pests? Perceptions of ecological change in China
Jennifer H. Zhao, Peter Ho und Hossein Azadi
Environmental Monitoring and Assessment
Volume 173, Numbers 1-4, 985-994, DOI: 10.1007/s10661-010-1439-yOpen Access
http://www.springerlink.com/content/rj34j3v323423086/

Abstract

In the past, scientific research has predicted a decrease in the effectiveness of Bt cotton due to the rise of secondary and other sucking pests. It is suspected that once the primary pest is brought under control, secondary pests have a chance to emerge due to the lower pesticide applications in Bt cotton cultivars. Studies on this phenomenon are scarce. This article furnishes empirical evidence that farmers in China perceive a substantial increase in secondary pests after the introduction of Bt cotton. The research is based on a survey of 1,000 randomly selected farm households in five provinces in China. We found that the reduction in pesticide use in Bt cotton cultivars is significantly lower than that reported in research elsewhere. This is consistent with the hypothesis suggested by recent studies that more pesticide sprayings are needed over time to control emerging secondary pests, such as aphids, spider mites, and lygus bugs. Apart from farmers' perceptions of secondary pests, we also assessed their basic knowledge of Bt cotton and their perceptions of Bt cotton in terms of its strengths and shortcomings (e.g., effectiveness, productivity, price, and pesticide use) in comparison with non-transgenic cotton.

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Discussion and conclusion
Through a comprehensive set of interrelated survey questions, we have provided empirical evidence of farmers’ perceptions on changes in sucking and other secondary pests. In the scientific literature, it is posited that secondary pests are likely to increase over time because of two factors: (1) the general ineffectiveness of Bt cotton against pests other than the bollworm and (2) a lowered dosage of pesticides in Bt cotton. As a result of this, secondary pests that would otherwise not have survived have a chance to emerge and, without additional pest control, could potentially evolve into primary pests (Xu et al. 2008, p. 1272; Men et al. 2004). Our study has found indications that support the possibility of such a scenario. Farmers stated that the main reason for adopting Bt cotton is its pest resistance and not the reduction in pesticide applications (the latter reason mentioned by less than 1%). This is a minute but critical difference as demonstrated below. There is no doubt that farmers are satisfied with Bt cotton, as it has effectively brought the bollworm under control (in the sample provinces, over 90% of the respondents indicated a decrease in bollworm incidence). On the other hand, farmers are also faced with rising secondary pests. The overall majority of the farmers answered affirmative to the question whether secondary pests had increased since the start of Bt cotton cultivation. The type and level of secondary pests perceived shows regional variation, but in all of the three cotton producing regions, a substantive proportion of the farmers (ranging from 30.9% to 97.1%) have perceived a “strong” increase of one or more secondary pests. As secondary pests increase, farmers will need additional sprayings over time. Rural surveys conducted shortly after China’s introduction of Bt cotton in 1996 reported reductions in pesticide applications. For instance, in 1999,    the research group led by Huang and Pray found a reduction in pesticide sprayings ranging from 12 to 3 times (Pray et al. 2001, p. 814; Huang et al. 2001, 2003; Pray et al. 2002). However, posing the same question 5 years later, we found that the average decrease in pesticide sprayings was significantly lower (five to six times).
 
Our survey results also indicated two other potential problems of Bt cultivation. First, we found that farmers have virtually no knowledge about Bt cotton and genetic engineering. A low level of understanding implies that farmers have no means to interpret possible agricultural production problems that they might encounter in the field. In particular, in the case of GM crops of which ecological effects are still insufficiently understood, it is important to raise farmers’ knowledge by stepping up agricultural extension and practical training.
 
Second, approximately a quarter of the farmers perceive a lower productivity of Bt cotton versus conventional varieties. In addition, close to 60% of the respondents finds that overall production costs have not decreased due to higher prices of Bt cotton seed. This result is in contradiction with that found in other research (Pray et al. 2001; Huang et al. 2001). As the bulk of our survey questions did not concern the economic profitability and productivity of Bt cotton, these two findings therefore deserve further investigation.
 
Various researchers have pointed to the potential environmental risks of Bt cotton (Qiu 2008; Wang et al. 2008; Qaim 2003, p. 2126). Due to the lack of scientific understanding of Bt cotton’s ecological impact and the fact that ecological changes can only be monitored and evaluated on a long term, it is vital to adhere to the precautionary principle when biosafety issues are at stake. Bt cotton has a good potential in improving worldwide cotton production due to its effective resistance against the bollworm. At the same time, because of an evident rise of secondary pests, it is critically important to closely follow and assess its commercial production in the field.