Bt corn is a form of genetically modified corn. According to a 2010 USA Today article, 85 per cent of all corn grown in the US is genetically modified. A large amount of this is Bt corn. Bt corn is considered genetically modified because it contain genes from another species---in this case, the foreign genes belong to a bacterial disease found in soil. This disease (Bacillus thuringiensis, hence Bt) contains naturally-occurring toxins that kill small insect pests. It is particularly helpful in killing the pesky corn borer.
Advantage: Less Pesticides, More Yield
The foreign bits of DNA in Bt corn concern some consumer watchdogs, but is also what allows corn farmers to reduce pesticide application without corresponding losses in yield and income. When pests that attack corn fields eat Bt corn, specific proteins attach themselves to the snacker's stomach and burn a hole through it. The pest dies of starvation. This is an advantage because if corn plants can fight off invaders themselves, there is less need for farmers to spend money and time on pesticide application. Lower amounts of pesticides are also better for the environment because it means less contaminants leach into surrounding areas and water supply.
Advantage: Cost Efficiency
Another good thing about Bt corn is that it is cost-efficient. In the eyes of experts, it is relatively simple to introduce Bt genes into crops and it is cheaper for farmers to buy Bt seed than to lose crops to pests or pay for and apply large amounts of pesticides.
Disadvantage: The Unknown
The biggest disadvantage of Bt corn is the murkiness of its long-term effect on environmental and human health, which are the same concerns expressed about other genetically modified foods. Though Bt corn is nothing new, some still claim that it could have negative effects on health. The idea is that if the Bt corn can kill bugs that eat it, maybe it could hurt human consumers as well. This is mainly a negative public relations issue for Bt corn producers, unless, of course, a case emerges that shows actual harm from eating genetically modified food. A more valid concern is how Bt corn affects the environment. Most of the borers and other pests that eat Bt corn die. However, some will not. Those that survive likely have built-in natural resistance to the poisonous proteins, and this resistance will be passed on to their offspring. In the long run, thanks to basic evolution, farmers may find themselves with pests that are resistant to the effects of Bt corn.