London (2.8.06) – Cotton production in China is very diverse. Some areas in drier, irrigated western China have large monocultures – like in Arizona and California – while in eastern China, where most of the Bt cotton is used, it is grown in small plots as a rotation crop that often follows winter wheat in a mosaic which includes corn and peanuts.

A recent report from Cornell University (1) (see suggested that problems had arisen with Bt-cotton in China: that while the boll-weevils for which the transgenic strain had been designed continued to be well-controlled, other pests (mirids) had taken their place with insecticide usage back to where it had originally been.

The paper in question was not peer reviewed; nor has it been published, appearing apparently only as a presentation at a conference. The paper’s data and conclusions have been challenged, most seriously by the Chinese scientist who provided the field data for the US analysts (2).

Huang Jikun, director of the Centre for Chinese Agricultural Policy, which provided data for the study, says the findings could be based on a faulty analysis. It is well-documented that insect species, including mirids and other secondary insect pests of cotton have yearly population fluctuations based on weather and other environmental factors independent of Bt cotton. Summer 2004 was cooler and wetter than normal, leading to mirid outbreaks on other crops nearby, not only on cotton. Much smaller populations of the mirids were present on those same farms in 2005 and 2006. Dr. Huang and his collaborators have been conducting large annual surveys since Bt cotton arrived in China, all of their work shows a large reduction in pesticide use. The group have published several papers in top journals.

While agreeing that it is very important to study and develop strategies against insects that are not affected by Bt, Huang said that the Cornell study underestimated the benefits of GM cotton by comparing differences in income between GM and non-GM farmers in 2004. By then, nearly ten years of farmers growing GM cotton had dramatically reduced the bollworm population on non-GM as well as GM and cotton farms, decreasing the amounts of pesticides used for both.

Pest management control in China may also have been wanting. The Cornell paper itself reports that integrated pest management is not always the practice in China: Empirical studies also show that Bt adopters in China sprayed way too much pesticides compared with optimal levels. Irrational behaviour of over-spraying discounts the benefits of Bt technology and causes downsize bias as well.

By improperly using new technologies farmers in developing countries may fail to realize the promised profits.

Cotton farmers in the U.S. and other countries who plant licensed Bollgard cotton are familiar with the need to monitor their crop for secondary pests and make insecticide applications as needed.

Moreover, secondary pests such as mirids typically are controlled with fewer sprays than the worm pests controlled by Bollgard cotton; therefore, farmers continue to see reduced insecticide costs by spraying for secondary pests only as needed.

A major benefit of legitimate, commercial distribution of Bollgard cottonseed in countries that enforce intellectual property rights facilitates the dissemination of product information to educate farmers on how to use new technologies most effectively.

Thus, cotton entomologists in the US and Australia have long anticipated, found, and addressed secondary pest problems in Bt-cotton which resulted from the reduced use of insecticides against bollworms. For decades, the main pest problem in California was mirids, replaced in recent years by cotton aphids (apparently an introduced biotype). For climatic reasons, bollworms were never really a problem so California was already something of a model for life with Bt-cotton. The south-eastern US has managed increased densities of stink bugs since Bt cotton. Australia anticipated increases in aphids and mirids, but has not had the aphid problems. Some growers in Australia have adopted trap crops using alfalfa for mirids, a strategy first proposed and trialled in Caliornia more than 30 years ago.

As so often in biology, the situation is not as clear as one might have thought from the original publication (2).


1. Seven-year glitch: Cornell warns that Chinese GM cotton farmers are losing money due to 'secondary' pests. Cornell University (July 26, 2006) (

2. Zi Xun. Cornell GM cotton study flawed according to Chinese scientist. Science and Development Network (31.7.06) (


  Further thoughts on Chinese Bt-cotton pests