by Matt McIntosh
Canada grows a lot of corn – and fittingly, it attracts lot of corn-specific pests.
Damage caused by the European Corn Borer and related species can be particularly severe. With a high enough pest population, farmers have to contend with yield losses, lower seed quality, and a greater risk of disease spreading in the crop. As with other crop-harming insects, farmers trying to control the corn borer use a range of strategies, often in combination.
One of those control tools is the bacterium Bt.
What is Bt?
The bacterium Bacillus thuringiensis (Bt) is a naturally occurring soil organism containing proteins effective at controlling several insects, such as flies, mosquitoes, Colorado potato beetles, and corn borers (including the aforementioned European variety). There are several strains of Bt corn. Each produces different proteins that control specific groups of insect pests. It has been used by farmers for this purpose for the better part of a century, though commercial availability of Bt as a spray picked up several decades later.
As a spray – or as a gene
Bt is still used in the form of a spray – that is, farmers can manually apply it to their crops to control specific insect pests. However, the genes which allow Bt to produce its pest-fighting proteins can also be incorporated into a crop’s genetic sequence. This allows the crop to produce the same proteins, meaning it can defend itself from specific insectoid attackers.
Because the development of Bt corn involved the incorporation of genes from a different organism, Bt corn is considered a GMO (genetically modified organism). In Canada, that means its approval and continued availability to farmers is controlled by regulations from two federal ministries – Health Canada, and the Canadian Food Inspection Agency.
One of many tools
Many Canadian farmers grow Bt corn varieties to defend against corn borer and corn rootworm (another major corn pest). Indeed, the technology has been very helpful to many a farmer, and for many a year.
But natural selection is always a factor. Insect pest populations like the corn borer can, and do, adapt over time to the proteins in the Bt bacterium. Such resistance can make the use of Bt much less effective. This is why farmers frequently use Bt sprays and crop varieties in combination with a variety of other growing strategies, including actively rotating crops (changing what crops are grown in the field each year), and adopting practices which support beneficial insects.
Resistance is a natural and inevitable process. Some portion of the insects in a population will naturally be genetically resistant. This typically starts out very low and unnoticeable. How quickly it can increase in a population is determined by the “selection pressure,” which refers to the factors that cause a population to change genetically. Having a field planted with 100 percent Bt corn would likely kill all of the susceptible pests, leaving only the resistant ones to produce resistant offspring in the next generation, and resistant pests would in time come to dominate the population. This high selection pressure must be avoided through resistance management practices to slow the development of resistant populations. Farmers and others use a variety of tools in order to prolong the life of Bt traits.
By using a combination of techniques – also called “Integrated Pest Management” – farmers can help prevent insect pests from going accustomed to Bt proteins, while reducing the need to control them with insecticide sprays.