impressum, Coccinella sp., Pseudophomus rufipes. Transgenics Planting rootworm-resistant transgenic corn is another strategy for minimizing damage. BT corn is effective at reducing root damage and is safer and often cheaper than insecticide. The transgenic traits, isolated from the common soil bacterium Bacillus thuringiensis strain (often referred to as Bt), produce the insect control protein. Bt was first discovered in 1901 by Japanese biologist S. Ishiwatari as the source of disease that was killing large populations of silkworms. Bt was first used as an insecticide in 1920 and spray formulations containing either Bt bacteria or Bt proteins came into use in the 1970s for crop protection, including organic farming operations. Bt insecticides saw expanded use and development in the 1980s as an alternative to synthetic insecticides. Beginning in the 1980s, the genes responsible for making Bt proteins were isolated and transferred into corn plants. Bt was commercially approved in transgenic corn seed in the mid-1990s. Compared to spray formulations, transgenic plants with the Bt protein provide much more effective insect protection throughout the season. Other Bt proteins have been used to genetically modify potatoes, cotton and other types of commercial corn. The two most common brands of transgenic Bt corn are Genuity and Herculex. Genuity Smartstax combines Monsanto's VT Triple Pro, Roundup Ready 2, and Acceleron Seed Treatment System technologies, as well as Dow Chemical's Herculex Xtra and Liberty Link technologies. Acceleron, Herculex Xtra, and VT Triple Pro include traits for protection from insect damage. Bt must be ingested to kill the insect. A susceptible larva eats the protein, which then binds to receptors in the larval gut. Binding initiates a cascade of effects that ultimately leads to death. Bt proteins are highly selective on certain categories and species of insects, eliminating insecticide use and its harmful effects to non-target organisms. Recently, however, strains of rootworms have been discovered in several Midwest US states that exhibit Bt resistance. According to Monsanto, the "YieldGard VT Triple and Genuity VT Triple PRO corn products" are affected. In 2009, four strains in Iowa were found to have field-evolved resistance to Bt corn. Some rootworms were found to be resistant to two or more Bt toxins in addition to being tolerant to crop rotation. This ability to rapidly evolve to adapt to multiple traits in their new food source has proved to be a big challenge for farmers and scientists. That same year, Monsanto, DuPont