The emerald ash borer is an insect that is thought to have been accidentally brought to the United States from China in shipping containers. It attacks ash trees, eventually killing the trees, destroying an important part of the ecosystem. The presence of the emerald ash borer in the United States can be used as an example of how humans have

purposely introduced an insect to correct a problem in an ecosystem
used an insect to remove one insect species and replace it with another
worked to increase the biodiversity in a particular area
altered the equilibrium in an ecosystem by introducing a new species