Bt Transgenic Plants do not harm Parasitoids

Rama Kant Mishra June 13, 2008

The ecological study conducted by Mao Chen and other researcher to evaluate the effect of Bt toxins to the parasitoides have shown the initial results that it does have any ill effect on them. Parasitoides are the organism which live on the host plant to complete its life cycle. Although the ecological safety of transgenic insecticidal plants expressing crystal proteins (Cry toxins) from the bacterium Bacillus thuringiensis (Bt) continues to be debated and raised as a concern. Much of the debate has recent times been focused on nontarget organisms, especially predators and parasitoids that help control populations of pest insects in many crops.

Development and commercialization of corn and cotton varieties expressing insecticidal proteins (Cry toxins) from Bacillus thuringiensis (Bt corn and Bt cotton) have offered an alternative to traditional synthetic insecticides for control of important agricultural pests. Bt corn and Bt cotton have been adopted by farmers in 22 countries to control lepidopteran pests such as corn borers (mainly Ostrinia nubilalis) in corn and the budworm-bollworm complex (Heliothis virescens, Helicoverpa spp., Pectinophora gossypiella) in cotton.

Although many studies have been conducted on predators, but only few reports have examined parasitoids, however some of them have reported negative impacts. None of the previous reports were able to clearly characterize the cause of the negative impact for the parasitoides.

In the present study to provide a critical assessment, researcher used a strain of the insect pest, Plutella xylostella (herbivore), resistant to Cry1C and allowed it to feed on Bt plants and then become parasitized by Diadegma insulare, an important endoparasitoid of P. xylostella. The results indicated that the parasitoid was exposed to a biologically active form of the Cy1C protein while in the host but was not harmed by such exposure.

Parallel studies conducted with several commonly used insecticides indicated they significantly reduced parasitism rates on strains of P. xylostella resistant to these insecticides.

These results have provided the first clear evidence of the lack of hazard to a parasitoid by a Bt plant, compared to traditional insecticides, and describe a test to rigorously evaluate the risks Bt plants pose to predators and parasitoids.