Transgenic Crops

One of the most recent, controversial, and potentially revolutionary areas of agricultural research is the development of genetically engineered, or so-called transgenic crops. Genetically engineered organisms are ones in which genes from different species have been
inserted in such a way as to permit those genes to express their characteristics in the host organism. In crop plants the focus has been on inserted genes from the bacterium Bacillus thuringiensis that trigger production of insecticidal compounds in the tissues of the host
plant. The number of different transgenes that have been used to confer insect resistance in crops approaches, but only B. thuringiensis transgenes have been commercialized. Transgenes also have been used to confer herbicide tolerance, drought or salt tolerance, or to alter the nutritional qualities of the crop. The relevance of pollinators to transgenic crop technology rests on two issues – the potential harm to pollinators posed by transgenic crops, especially insecticidal ones, and the potential harm to the environment caused by pollinators spreading transgenes into wild plant populations.

Transgenic insect resistance is seen to have numerous advantages over conventional insecticides. It provides more targeted delivery of a toxin to the pest, greater resilience of the toxin to weather or other forms of biodegradation, reduced exposure risk to the applicator, and reduced use of conventional broad-spectrum insecticides and their associated risks to the environment. But there has been concern that engineered toxins, whether in the plant’s tissues or in its nectar and pollen, could be detrimental to bees. Fortunately, that risk seems small at this time. A sizeable research record has shown that B. thuringiensis toxins, whether conventional or engineered, are generally benign to bees. The risk from other candidate engineered toxins, namely the pesticidal proteins chitinase, glucanase, and cowpea trypsin inhibitor.

Another area of concern with this new technology has been the potential of transgenes ‘escaping’ from engineered crops into wild plant populations with unknown and perhaps detrimental effects. Chief among these concerns is the potential for transgenes for herbicide tolerance becoming incorporated into weedy species, thus making them more difficult to control. Bees, because of their pollen-collecting habit and catholic flower preferences, are seen as primary vehicles for the spread of such transgenes. One solution to the problem may be a buffer zone of conventional crop plants grown around the transgenic ones. Pollinators visiting the transgenic plants may subsequently deposit much of their plant-available pollen on to conventional crop flowers in the buffer zone before leaving the area to visit other plant species or to return to the nest. It is unlikely that buffer zones alone will solve the problem in all cases. In one study, honey bee colonies were placed at a distance of 250 m from a field of transgenic herbicide-tolerant maize. The transgenic field was surrounded by a 3 m buffer zone of conventional maize. Of the pollen samples collected from the colonies, 52% contained the transgene for herbicide tolerance; thus the 3 m buffer zone did not prevent the spread of the transgene. There is evidence that most of the pollen from a particular plant is deposited by a bee forager on to the next few subsequent flowers visited, but some pollen can persist for up to the 20th subsequent flower. Ongoing research is concentrating on gene flow from transgenic crops, the competitiveness of transgenic plants, the efficacy of isolation distances, and the interactions of bee foraging behaviour with pollen movement among plants.

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