During the past 10 years, a wave of maternally transmitted microbeshas swept through nonpest fruit fly populations in California andacross the country. UC Davis population biologists, who closelymonitored the microbe wave from its early stages, have produced unusual studies, believed to be the only such detailed analysis quantifying the natural dynamics of a gene-like transformation of whole populations. Their work has laid a foundation for other researchers who are investigating how to harness this powerful microbial tool, according to Michael Turelli, director of the UC Davis Center for Population Biology. The tool eventually may be used to manipulate populations of pest insects, such as controlling harmful agricultural pests like Medflies or, more subtly, to alter the ability of certain insects to transmit diseases to animals and people. The most complete analysis of the system is published in a recent issue of the journal Genetics. The microbe, known as Wolbachia, infects nearly all the offspring of infected fruit fly females, whether they mate with infected or uninfected males. But when uninfected females and infected males mate, they produce only about half the usual number of offspring. That reproductive disadvantage rapidly spreads through the population; several populations jumped from less than 20 percent infected to more than 80 percent within two years. Other studies have suggested Wolbachia are ubiquitous and may be able to sweep through many species.