More than half of what Americans consume has been genetically modified. It is not labeled in the United States; corn, soybeans and rapeseed oil are all GM foods that are found in cereals, snacks, beverages. GM foods have been engineered to resist herbicides, to improve nutritional content, to resist insects pests and other reasons. People fear that cross contamination may occur between GM and non-GM foods. They fear the creation of some new pest, or antibiotic resistance, or that foods may contain new allergens or toxins. Another fear is that when a crop is genetically modified, the former pest of that crop no longer eats it and now, this pest dies off. The pest may have provided food to another organism in the food web. This may harm biodiversity and lead to extinctions. Bacteria have been genetically modified as well as viruses. Some fear this can lead to the emergence of new diseases. However, most opinions in the various research agree that this is a new area that still needs investigating in terms of the pros and cons of genetically modified foods.