Pea aphids are often under attack by wasps seeking to lay their eggs inside aphids, turning them into an all-you-can-eat buffet for the larval wasps.

The aphids vary in their resistance to the wasps, which scientists had chalked up to genetic differences between aphids.

But it's not in their genes at all -- the wasp-resistant aphids owe their lives to the symbiotic bacteria carried inside them, according to new research.

"We knew there was a tremendous amount of variation in resistance to parasitism among different aphid lineages," said Kerry M. Oliver, lead author on the report. "We were definitely surprised we assumed the bulk of the resistance was due to the aphids' genotype."

Figuring out what makes insects resistant to natural enemies is important to farmers. Pea aphids can be agricultural pests on plants in the pea family including lentils and peas.

The new finding suggests why some lineages of aphids readily succumb to the wasps and others don't.

"This work shows the difference can be attributed to the symbionts, not to the aphid genotype," said Oliver, a postdoctoral research associate in The University of Arizona's department of entomology and a member of UA's Center for Insect Science.

Oliver added that this implies aphids could acquire resistance to natural enemies by picking up bacterial symbionts, rather than having changes in the aphids' genes. Such a newly acquired resistance is heritable, because the bacteria get passed down from mother to her offspring.

The article by Oliver and his co-authors Nancy A. Moran, UA Regents' Professor of ecology and evolutionary biology, and Martha S. Hunter, UA associate professor of entomology, is published this week in the online early edition of the Proceedings of the National Academy of Sciences. The U.S. Department of Agriculture funded the re
'"/>

Contact: Mari N. Jensen
mnjensen@email.arizona.edu
520-626-9635
University of Arizona
25-Aug-2005