Pest-proof crops hard work

By PHILIPPA STEVENSON agriculture editor

Farmers looking forward to better pest management as a payoff from transgenic crops are likely to find they are not as easy-care as expected.

Crop and Food Research scientist Dr David Teulon warns that crops with built-in insect resistance, such as Bt potatoes and brassicas, may need more work than conventional plants.

Christchurch-based Teulon's results from research done last year at New York's Cornell University were published only last month, after he presented his findings to the Plant Protection Society's annual conference.

His conclusions on the mixed benefits of using transgenic plants in pest control are strikingly similar to those released last week by the UK Soil Association.

The British report, Seeds of Doubt - North American farmers' experiences of GM crops, said genetically modified crops had been an economic disaster in the US and Canada.

On the ability of Bt crops to reduce insecticide use, the report said modern integrated pest control methods could achieve adequate control and Bt plantings were not being used to replace insecticides, but in addition to them.

The document was hailed by the Green Party for giving new weight to its call to maintain New Zealand's moratorium on the commercial release of GM organisms, which is due to be lifted in October next year.

But it was criticised by the pro-GM Life Sciences Network and Federated Farmers as politically motivated.

Life Sciences chairman Dr William Rolleston said the report was misleading and could not be relied on for an accurate picture of the situation in the US and Canada.

Federated Farmers spokesman Neil Barton said the GM crops in the report were of little interest to New Zealand farmers, who did not grow cotton or soybeans and only a limited area of canola.

"New Zealand farmers will be interested in the next generation of GM products which could potentially produce human health benefits, such as nutraceuticals."

Farmers could not afford to ignore the chances GM products offered in environmental sustainability, productivity and health benefits if consumers demanded them. Barton said.

Teulon's paper examined the benefits and costs of transgenic plants in relation to pest management in New Zealand.

He said it had received little feedback since it was published on the Hortnet website three weeks ago, but he had a good response from fellow scientists at the Plant Protection conference who regarded it as a "nice summary".

Transgenic plants had the potential to lift crop yield and reduce insecticide use on New Zealand farms, but the benefits would depend on several factors, including the plant species, its mix of insect pests, environmental conditions and alternative pest management tools.

The most pressing issue for transgenic plant use was the potential for rapid development of insect resistance, Teulon said.

"Already, about 17 insect species have become resistant to Bt in the laboratory, but only one species has shown widespread resistance in the field." It was widely considered to be only a matter of time before resistance occurred to Bt plants.

In the US, particularly, insect resistance management (IRM) was being developed "as a matter of high priority".

The IRM strategy likely for New Zealand would be the use of plants containing high concentrations of Bt combined with nearby insect refuges of non-transgenic plants.

The proposition entails Bt-free refuges in which a population of toxin-susceptible insects are maintained for mating with their Bt-resistant cousins to prevent the resistant insects becoming dominant.

"In New Zealand, IRM strategies are being considered for two Bt crops," Teulon said. "Results to date suggest sufficient potato tuber moths would forage between adjacent transgenic and non-transgenic potato crops to minimise development of insecticide resistance."

However, preliminary research indicated that might not be true for the diamond back moth in brassica crops. The moth had already developed resistance to Bt pesticides in several countries.

Comparisons of the benefits of transgenic crops had been made only with conventional farming and might not be valid when compared with other management systems, he said.

"For example, integrated pest management [IPM] systems have led to dramatic reductions in insecticide use in apple, kiwifruit, processing tomatoes, and brassicas in New Zealand."

Transgenic plants and IPM both allowed for the more targeted use of insecticides, but he warned that "both systems may delay the development of ecologically based pest management, and pursue a genetic treadmill of solutions in the race against resistance".

One of the challenges in pest management would be to evaluate how and if transgenic plants could be incorporated as safe, effective components of sustainable IPM systems.

* Bt or Bacillus thuringiensis is a naturally occurring soil bacterium which produces an insecticidal toxin. Its role in nature is not well understood, but it has become the most important bio-pesticide, accounting for about 90 per cent of all commercial bio-pesticide sales worldwide. It is used by organic farmers as a form of biological pest control. Crops transformed with genes derived from Bt are also the most common transgenic plants released into the environment because Bt affects a range of insects but has relatively low toxicity to non-target species, including humans.

New Zealand Plant Protection Society

North American farmers' experience of GE crops

Further reading
nzherald.co.nz/ge

GE links

GE glossary


Further reading
nzherald.co.nz/environment