Genetic crop pollution

When a genetically engineered plant reproduces itself, it may kill other plants or animals in unforeseen ways due to its modified genetic structure.
It was reported that the pollen of corn genetically engineered for pest resistance, when dusted on the leaves of milkweed plants caused the death of 44% of monarch butterfly caterpillars feeding on the milkweed. Caterpillars feeding on pollen from unmodified plants survived. In 1999, nearly 25% of the USA corn crop contains this toxin gene.
Scientists are asking why the pollen was not tested before the plants were planted on millions of acres of farmland.
(G) Very specific problems