Monarch butterfly larvae harmed by transgenic pollen

At the Cornell University a group of scientists have discovered that larvae of the Monarch butterfly were harmed from eating leaves powdered with pollen from genetically engineered corn containing genes from Bacillus Thuringiensis (Bt).

The purpose of inserting the Bt gene is that it makes the plant produce the Bt toxin that kills some important insect pests. In most cases the gene is expressed in most parts of the plants including the pollen.

During pollination periods, large numbers of the pollen are shedded. Considerable numbers of them land on the leaves of plants in the vicinity of the pollen source. They are dispersed at least 60 meters outside corn field by the wind.

The scientists mimicked this situation by powdering milkweed leaves with pollen from transgenic Bt corn. The pollen density on the leaves was set to match the density found on milkweed leaves from corn fields.

The growth and survival of Monarch Butterfly larvae that feed on milkweed leaves was studied. 56% of larvae that fed on leaves powdered with Bt corn pollen died, while no larvae feeding on leaves powdered with natural corn pollen died. In the surviving larvae, the the feeding rate was considerably lower, which led to slower growth rates. At the end of the experiment, the weight of the larvae was less than half that of the larvae feeding on leaves with natural pollen.

The scientists conclude that these results have potentially profound implications for the conservation of monarch butterflies.

Comment

This result has important implications for agriculture. In this case only one of the large number of insects existing in or in the vicinity of cultivated fields was studied. It cannot be excluded that many other moth and butterfly caterpillars, including endangered ones, may be at risk from Bt corn.

This kind of effect from genetically engineered "pesticidal plants" might seriously upset insect ecology. It would be very harmful to agriculture if such an effect would upset the delicate balance between different insect populations in such a way that the numbers of a beneficial predating insect is greatly reduced. Then there might be a problematic overgrowth of pests.

More serious is what might happen when the genes are transferred to related plants and weeds. For example in the case of corn there are a number of wild relatives in Latin and South America. Cultivation of GE corn will lead to an uncontrolled spread of genes in the wild populations. In the long run, pollen with pesiticidal genes might cause irreparable damage to the insect population in large regions. The ecology of insects is complex and any upset of the delicate balance between different insects might have unpredictable effects not only on the insect ecology but also on plants, trees and birds.

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