University of Arizona entomology professor Molly Hunter has received a $520,000 National Science Foundation grant to explore bacterial manipulation of insect reproduction.
In the three-year study, Hunter and her team will research the genomic and cytological mechanisms used by the bacterium Cardinium to manipulate reproduction of parasitic wasps that attack whiteflies, a growing agricultural pest concern.
The bacteria are inherited in the wasps. Unlike a pathogen or a disease, the only way the bacteria can spread is by manipulating the reproductive systems of their hosts.
"The bacteria are unusual in this way," Hunter said. "They're parasites, but because they're inherited, they're intimately involved with the evolution of their host. They're influencing reproduction of their hosts in a way that benefits their transmission to the next generation."
Hunter's research centers on a reproductive manipulation called cytoplasmic incompatability, or CI.
In the wasp population, both males and females get the bacteria from their mother, transmitted in the egg. So, in males, the bacteria is at a dead end, unable to be transmitted to offspring.
However, the bacteria in the male sabotage the reproduction of uninfected females so the females do not produce any offspring, in this way depressing their fitness. Females that have the bacteria can mate with anybody, males that have the bacterium or males that don't have the bacterium.
"Once this gets going in a population, over generations, the bacterium just spreads and can spread until they all have it," Hunter says.
Another bacteria, Wolbachia, is present in an estimated 20 to 40 percent of insects, and the most common function of Wolbachia is CI. While there is little overlap in gene homology between Wolbachia and Cardinium, both can cause CI.
"This is a very common phenomenon in nature that we're only beginning to get our heads around in terms of understanding how it affects the evolution of insects," Hunter said. "We have two unrelated bacteria that cause this same effect and we're interested in the molecular mechanism of CI."
The focus of the grant is furthering the basic biological understanding of Cardinium that causes CI, and comparing it to the better-known Wolbachia. With better knowledge at the molecular level, applied scientists can begin studying ways in which CI might be used to control agricultural pests.
Because CI-causing bacteria spread in host insects, they could be used to bring in genes for control or genes that prevent virus transmission. For example, the sweet potato whitefly is the worst pest of cotton in Arizona and one of the world's most invasive insect pests.
"We're going to learn more about how these bacteria work and how CI works," Hunter said. "Then we'll understand a bit more about how we can use them in another context to control pests such as the whiteflies."