The next generation of pesticides
By Jonathan Lundgren
USDA-ARS Research Entomologist
Every year, the fate of the entomological world is discussed by 2,000 to 3,000 entomologists at the annual meeting of the Entomological Society of America (this year held in Knoxville, Tenn.). Often, a hot topic is clearly identifiable from this meeting. This year is no exception: the major theme of the meeting was nothing less than the next generation of insecticides: RNAi-based insecticides.
This is important, and everyone should know what is coming down the pike.
First, let's talk about what RNAi, or interference RNA, is. As an ecologist, my eyes tend to glaze over when I find that nucleic acids are the item on the docket. But I think this topic can be rendered fairly painless.
Genes produce proteins, and proteins are the workhorses of life. They act as enzymes, they provide the structural building blocks of cells, and they perform numerous functions within these cells. Life hinges on the ability of DNA to produce proteins.
When a cell wants to make a protein, it activates a particular gene. When the cell wants to stop making a protein, it turns the gene off using various methods. One way that cells turn a gene off is by sending in a small fragment of RNA that suppresses the gene's expression into a protein. This process is called RNA interference, or RNAi.
The implications of RNAi (which was only discovered 15 years ago) are enormous. Just by knowing the DNA sequence of a gene, researchers can cheaply create a small molecule of RNA and send it into a cell to block protein production by the gene--functionally turning the gene off.
By flipping a gene off and watching, we can figure out what each gene does. If we know the DNA sequence that produces diseases like cancer, maybe we can turn off the offending genes and kick cancer in its molecular crotch. These two uses of RNAi are called functional genomics and gene therapy.
Scientists are interested in using RNAi for all sorts of things, including using RNAi to silence critical gene function in insect pests, thereby killing them. The eddy of this concept has turned into a tidal wave, and 78 presentations at the EntSoc meeting this year pertained to using RNAi in insect research and control.
Arguably, seed companies are a driving force in this discussion. They have created a genetically modified corn plant that produces small RNAs that silences a gene in the western corn rootworm, the most costly pest of agriculture in the world. Efforts are also underway to develop RNAi sprays that can be applied to households or the environment that will silence pest genes, thereby killing them.
The instant question that comes to most people's minds is likely "err...is this safe?" All indications are that RNAi can be very specific to the target gene. And we eat small RNAs with every meal, and to our knowledge it doesn't seem to hurt us.
However, nearly all previous work on RNAi has been relegated to individual cells in a Petri dish, or to individual organisms (e.g., a sick grandma). Genetically modified crops are currently planted on nearly 10 percent of the terrestrial land surface of the United States. If RNAi-based pesticidal crops are planted on a similar scale, then this is an environmental exposure that is orders of magnitude greater than anything we have experienced before.
Whether you love the idea of this new technology or hate it, the proliferation of this next generation of insecticides seems as though it will be a part of our lives in the very near future.