Bacillus thuringiensis (Bt) is a common natural resource potentially used as a biopesticide. With the advent of genetic engineering, Bt genes have been inserted directly into several crops and have become widely commercialised. However, Robin Jenkins argues such large-scale use of Bt crops renders target insects liable to develop resistance against Bt. He claims that the agro-industries' ambition of mass marketing Bt crops will eventually make Bt biologically useless to farmers.

By Robin Jenkins

August 1999

Bt is a naturally occurring soil bacterium that is found throughout the world. When a specific strain of Bt is ingested by certain insect grubs, it may lyse their guts and kill the insect.

Originally identified in 1913, this natural insecticide was first commercialised as a dust or spray just after World War II, and has been used in organic agriculture. By 1980, faced with the environmental problems associated with chemical pesticides, most of the biggest agro-chemical companies were producing Bt sprays as a safer and more selective alternative.

With the introduction of Bt crops, agro-industries are promising several agronomic advantages. Bt crops, such as maize, cotton and potatoes, remain constantly protected since the toxin can be expressed throughout the growing season.

This is unlike Bt sprays, which are effective for a maximum of only three to five days. Furthermore, Bt crops are effectively protected against insect pests that tunnel inside the plant and cannot be reached by Bt sprays.

In 1995, the first Bt crops were approved by the United States Environmental Protection Agency (EPA) on condition that the companies produced plans for the management of insect resistance. The research focus shifted to how resistance can best be delayed rather than whether it could be prevented.

The industries were then optimistic that when insects became resistant to a Bt crop, they could easily replace the Bt with a different strain. However in 1996, Tabashnik, an entomologist at the Hawaii University, showed that a single insect gene could confer resistance to a number of Bt strains, including strains with which the insect had had no prior contact.

Due to EPA requirements, companies such as Novartis (Switzerland) and Monsanto (USA) have commissioned academic entomologists in the USA to devise resistance management strategies. These strategies call for a high expression level of Bt crops, in conjunction with the planting of non-Bt crops, which are supposed to act as a refuge for non-resistant insects. Through selection pressure, the strategy aims to diminish the likelihood of dominance of Bt- resistant insect populations.

Monsanto was willing to settle for a 4% refuge if no insecticides are used, or a 25% refuge, if chemical insecticides are allowed. The strategy is based on a mathematical model of insect population behaviour, but there is no field evidence to show that it works. Many entomologists from the US are even arguing for bigger refuges.

To add to the controversy, at an EPA hearing in February 1998, several US entomologists claim that the Novartis Bt 176 maize does not express the Bt toxin with sufficient uniformity to meet the criteria of the high dose/refuge resistance management strategy. This implies that resistant insects are likely to become the dominant insect population more quickly with the Novartis Bt maize than with the Bt maize developed by Monsanto and others who claim to meet the resistance management requirements. Hence, the Novartis Bt maize could potentially endanger the potency of other Bt maize varieties.

As a compromise, Novartis is currently recommending an even bigger 40% refuge of non-Bt maize grown with Bt maize. To date, this proposal has been refused by other companies since it greatly limits the market of Bt crops and hence they would no longer be profitable to sell.

In the case of Bt maize, the EPA has publicly admitted that a single, comprehensive resistance management strategy is practically impossible since five competing companies have produced several different products, each expressing the Bt toxin differently within various parts of the plant and over the growing season. Maize stem borers could avoid high Bt toxin releases by moving for instance, from Pioneer (USA) Bt maize to Novartis Bt maize at the right time.

Moreover, if the movement of resistant insects to a refuge area is high enough, these insects could pass their resistance gene to a susceptible population. Hence, to manage insect resistance to Bt crops, several strategies are required. This could be problematic to implement for large-scale agriculture, which thrives on the efficiency of uniform technology and its corresponding uniform production system.

The notion so dear to the industries that Bt crops feed the hungry, clean up the environment, and make agriculture more sustainable has no scientific basis. Bt crops are mere products in the struggle for global domination of life industries now being fought between the giants Monsanto and Novartis. Ordinary farmers worldwide will soon find out that Bt sprays no longer work, thanks to the biotechnology industries. - Third World Network Features

About the writer: Robin Jenkins is a consultant for Genetic Resources Action International (GRAIN). The above article first appeared in Biotechnology and Development Monitor (No. 38, June 1999).