In a case of rapid evolution, bacteria have been found to give whiteflies – crop-damaging insects of global importance – an edge over their uninfected peers, new research from the University of Arizona suggests.

In just six years, bacteria in the genus Rickettsia spread through a population of the sweet potato whitefly (Bemisia tabaci), an invasive pest of global importance. Infected insects lay more eggs, develop faster and are more likely to survive to adulthood compared to their uninfected peers. The discoveries were made by a University of Arizona-led team of scientists and are published in the April 8 issue of the journal Science.

It's instant evolution," said Molly Hunter, a professor of entomology in the UA's College of Agriculture and Life Sciences and the study's principal investigator. "Our lab studies suggest that these bacteria can transform an insect population over a very short time."

"It is not uncommon to find a microbe providing some benefits to their hosts, but the magnitude of fitness benefits we found is unusual," she added.

In addition to the observed evolutionary advantages – which biologists call fitness benefits – Hunter's team discovered that the bacteria manipulate the sex ratio of the whiteflies' offspring by causing more females to be born than males.

According to Hunter, the bacteria are transmitted only through the maternal lineage (from mother to offspring). Therefore, it is beneficial for them to make sure more female than male whiteflies are born.

"However, we don't know how they're doing that yet," she said.

Anna Himler, a postdoctoral research associate in Hunter's lab and the lead author on the research paper, said her team was most surprised by the speed with which the bacteria moved through the whitefly population.

In 2000, the researchers found Rickettsia in only 1 percent of the whiteflies in Arizona. In 2003, the microbes had spread through half of the population, and today, almost all whiteflies in Arizona contain the bacterium.

Whiteflies come in many different species and variants within species called biotypes. Of those, none are considered as detrimental to agriculture as the "B Biotype" of the sweet potato whitefly, which originated in the Mediterranean.