When marauding Vikings decided to settle down they usually "went native,'' marrying local girls and blending in. Invading honey bees may be doing the same. The invasion of new bee populations has attracted attention in recent years with the spread of so-called Africanized, or "killer bees'' moving north from South America.

When a new strain of bees invades a region already populated by honey bees, they interbreed and gain benefits from the genes of their predecessors, researchers report in this week's edition of Proceedings of the National Academy of Sciences.

Charles W. Whitfield, an assistant professor of entomology at the University of Illinois at Urbana-Champaign studied the genes of bees in Africa, Europe, Asia and the Americas, focusing on regions where several bee invasions have occurred, such as Brazil and South America.

Whitfield's team found that when invading bees were interbreeding with those already present, the combined genes were not just joined randomly.

"We asked the question: Is hybridization an essentially random process?'' co-author Amro Zayed said in a statement.

When the African honey bees mated with the western European honey bees that had been in South America for centuries, one might expect that the hybrid offspring would randomly pick up both the functional and nonfunctional parts of the genome, he said.

"But actually what we found was there was a preference for picking up functional parts of the western European genome over the nonfunctional parts.''

This combination seemed to give the newcomers an advantage over their predecessors, though the researchers were not able to determine exactly how the new bees benefited.

It may be that certain traits are beneficial to survival in an area, or it may simply that being a hybrid of beneficial in general, they said.

The research was supported by University of Illinois and the National Science and Engineering Research Council of Canada.