It appears to be a case of high-speed evolution. Many arthropods — the large group of invertebrates that includes insects and crustaceans — are hosts of symbiotic bacteria inherited through the maternal line. The sweet potato whitefly, an agricultural pest, has acquired a new one.

Over a six-year period, a bacterium from the genus Rickettsia swept through the whitefly population, assuring survival advantages for the whiteflies and for itself. The new research appears in the April 8 issue of Science.
“Whiteflies that have this infection have greater fitness, at least in the laboratory,” said the senior author of the study, Martha S. Hunter, a professor of entomology at the University of Arizona. “We’ll be testing whether this fitness benefit exists in the field as well.”
Compared with uninfected whiteflies, infected insects develop faster, are more likely to survive to adulthood and lay more eggs. Moreover, the bacterium induces the insects to produce a larger number of daughters, advantageous for a bacterium that is passed to the next generation only by the females.
Infected sweet potato whiteflies now flourish across the Southwest. As of 2008, 94 percent of whiteflies were infected, compared with 1 percent in 2000.
“This study shows that acquiring a bacterial symbiont can fundamentally change the biology of an insect, really instantaneously,” Dr. Hunter said. “And what results is really a different animal than what was there before. This is something we want to know about for pest management. We want to know whether a bacterium can make an insect a worse pest.”
(Source: The NYT)