<P> Unintentional introductions occur when species are transported by human vectors . Increasing rates of human travel are providing accelerating opportunities for species to be accidentally transported into areas in which they are not considered native . For example , three species of rat ( the black , Norway and Polynesian ) have spread to most of the world as hitchhikers on ships . There are also numerous examples of marine organisms being transported in ballast water , one being the zebra mussel . Over 200 species have been introduced to the San Francisco Bay in this manner making it the most heavily invaded estuary in the world . There is also the accidental release of the Africanized honey bees ( AHB ) , known colloquially as `` killer bees '' or Africanized bee to Brazil in 1957 and the Asian carps to the United States . The insect commonly known as the brown marmorated stink bug ( Halyomorpha halys ) was introduced accidentally in Pennsylvania . Another form of unintentional introductions is when an intentionally introduced plant carries a parasite or herbivore with it . Some become invasive , for example the oleander aphid , accidentally introduced with the ornamental plant , oleander . </P>
<P> Unintentional introductions occur when species are transported by human vectors . Increasing rates of human travel are providing accelerating opportunities for species to be accidentally transported into areas in which they are not considered native . For example , three species of rat ( the black , Norway and Polynesian ) have spread to most of the world as hitchhikers on ships . There are also numerous examples of marine organisms being transported in ballast water , one being the zebra mussel . Over 200 species have been introduced to the San Francisco Bay in this manner making it the most heavily invaded estuary in the world . There is also the accidental release of the Africanized honey bees ( AHB ) , known colloquially as `` killer bees '' or Africanized bee to Brazil in 1957 and the Asian carps to the United States . The insect commonly known as the brown marmorated stink bug ( Halyomorpha halys ) was introduced accidentally in Pennsylvania . Another form of unintentional introductions is when an intentionally introduced plant carries a parasite or herbivore with it . Some become invasive , for example the oleander aphid , accidentally introduced with the ornamental plant , oleander . </P>
most exotic species are introduced into a new environment accidentally as a result of
most exotic species are introduced into a new environment accidentally as a result of
human travel
human travel