Bt-transgenic plants: negligible effects on beneficial insects

press release of February 21, 2006

Transgenic cotton or maize crops expressing Bt toxins have no direct effects on beneficial insects. Researchers of the National Centre of Competence in Research (NCCR) Plant Survival have concluded that the activity and abundance of non-target organisms that feed on pests in Bt crops are equivalent to those observed in non-transgenic cotton and maize crops.

The bacterium Bacillus thuringiensis (Bt) is known to produce an insecticidal protein that is useful for the control of insect pests. Transgenic plants are equipped with the same capacity, as a gene from the bacterium was inserted in the plant's genome. Today, Bt maize and cotton are grown extensively worldwide. In 2004, these crops covered 22.4 million hectares, a 25% increase compared to the previous year.

To find out the effects of these transgenic plants on non-target insects, three researchers from the federal research station Agroscope FAL Reckenholz in Zurich have reviewed results from a large number of studies on the subject. Jörg Romeis, Michael Meissle and Franz Bigler have published their conclusions in the January 2006 issue of the journal Nature Biotechnology.

Since the insecticidal protein is toxic for certain insect pests, adverse effects on beneficial insects (predators or parasitoids) were examined. These beneficial organisms help to regulate pest populations by either feeding on herbivores as e.g. ladybeetles do or by laying their eggs in larvae of pests as done by parasitoids. Hence, it is of importance that the insecticidal protein does not compromise the survival of these beneficial insects that play such an important role for sustainable crop production.

The studies evaluate the impact on insects living within different transgenic crops, such as maize or cotton. There are no indications that Bt plants have direct effects on natural enemies of pests, whether they are consuming the toxin by directly feeding on the plant, or by attacking herbivores insensitive to the toxin they ingested.

However, laboratory and greenhouse studies have shown negative effects on beneficial insects when living solely on herbivores (prey and hosts) that were adversely affected after having ingested the toxin. These effects, which were obtained in worst case scenarios are not due to the toxin itself or to genetic engineering, but rather because the reduced quality of the herbivores (prey or host). Such indirect effects are well known and accepted in chemical pest control. 

The data available to date reveal a high level of compatibility of today's Bt plants with biological control organisms. However, the researchers of the NCCR Plant Survival are cautiously avoiding generalisations. "The currently available data do not allow us to proclaim the safety of other insecticidal proteins that could be expressed in future transgenic crops". The analyses need to be carried out on a case-by-case basis.

Original article:



Agroscope FAL Reckenholz
Dr. Jörg Romeis
tel +41 44 377 7299

Dr. Franz Bigler
tel +41 44 377 7235