Using long fruit pickers, a UC Davis research team fans out along Putah Creek, plucking the tiny homes of gall wasps from the branches of oak trees. These small, round growths, created by California oak gall wasps, protect their larvae. In the lab, researchers are raising the insects and searching for clues about this cryptic species that’s all around yet rarely noticed.

Animal biology major Kora Hermida and Marshall McMunn, an assistant professor in the Department of Entomology and Nematology, hope to collect enough galls to uncover evidence of an elusive male and study the species' genetic diversity.

“Kora and I are raising these wasps, we’re extracting the DNA from the wasps and we’re going to sequence the DNA to try to figure out if there is enough genetic variation to suggest that there are males in this population,” McMunn explained.

McMunn says inside the gall, wasps grow from larvae to pupae, and when they fully develop into adults, they chew their way out. They’re especially abundant during the fall. To McMunn, it’s a fascinating insect. He said they’re not great at flying and adult wasps typically do not eat, as their primary focus is reproduction.

For Hermida, there’s another interesting aspect to these wasps. “The cool thing about this species is they’re not intimidating,” Hermida said. “They don’t have a stinger.”

Wasp collection

The researchers have collected hundreds of galls from all around Davis. The galls, firm and ranging in size from a marble to an apple, are stored separately in containers and cataloged by location. As wasps emerge from the galls, Hermida and McMunn carefully place them into vials. Since the wasps are tiny, it’s not always easy to get them to cooperate. To help, Hermida uses a tool that gently sucks the wasps from the container into the vial.

“When they come out, that’s when the fun happens,” Hermida said. “One of the galls had 16 so far come out and counting, another had 15 or 20 over the time we’ve been checking them.”

So far, they’ve seen more than 400 wasps emerge from the galls. 

DNA analysis

The researchers will work with the UC Davis Genome Center to conduct genetic tests. McMunn said male wasps have not been found in this species yet, but DNA analysis can reveal whether males are present in a population.

“We’re trying to look at the genetic variation across individuals,” McMunn said. “We’re looking at about 100 wasps and we want to see if they are genetically identical or if they differ between collection locations or just by individual wasps. We’ll use those patterns of genetic similarity to determine if there are males contributing variation to this population.”

DNA analysis can help the researchers understand how oak gall wasps reproduce. In most species, reproduction is primarily parthenogenetic, meaning females reproduce without mating.

McMunn is also curious about the wasp’s microbiome and behaviors, such as their feeding habits. He plans to offer sugar water to some of the insects to see how they respond. Studying these tiny insects, which thrive in local trees, could reveal important connections in the area’s ecosystems.

“There are dozens of these trees on my bike ride home, they’re everywhere. It’s part of our landscape that we don’t interact with much,” McMunn said. “For us, we’re fascinated by this really charismatic species that’s locally abundant and available for undergraduate research, they come out in the fall, and we can answer these fundamental biology questions.”