Oxford's cicada populations show shifts across generations

Miami University Ph.D. student Alfredo Ascanio Moreno uncovered how Oxford’s cicada populations have shifted over time in a 2021 study, with some habitats showing sharp declines and others surprising booms.

Moreno is an international graduate student who first arrived in Oxford in 2019 from Venezuela.

His day-to-day work as a graduate student consists of computational ecology, which is a disciplinary field that consists of developing theories regarding species distributions. This includes determining “how we understand where they are, where they are going to be and how we compare the requirements that species need in their environments,” he said.

Moreno explained the value that cicadas create for any ecosystem.

“The fact that they develop underground means that they help nutrients move up and down the soils,” said Moreno.

Additionally, these insects dig tunnels underground during the subterranean stage of their lives – these tunnels are used by different insects and bugs in the soil as well.

Cicadas also act as a healthy serving of protein for “birds, lizards, small mammals, and even humans, historically,” according to Moreno.

Moreno first got into this cicada study from one of his students, who had just gotten into the Research Experience for Undergraduates (REU) program through the U.S. National Science Foundation (NSF). The student was interested in cicadas and field ecology, so she focused her study on cicada broods, which are made of cicadas coming out of the ground in large numbers periodically. 

“If my student wants to do something, if it’s feasible, we are going to do it,” Moreno said.

Moreno, who studied marine and experimental ecology in Venezuela, said studying a new topic was a huge draw for him.

Moreno added that having cicadas periodically come out from under the ground is something new to him. According to him, Venezuela doesn’t have “something as massive and weird as cicadas emerging from the ground every 17 years or 13 years.”

Moreno spoke to some Miami professors who were able to provide data from 2004 regarding the emerging cicada broods, as well as a cicada study from 1987.

Moreno and his student had to “race against time” in order to get permission from private property owners to conduct their study. Once permission was granted, Moreno’s team began to set up traps.

Their 2021 study was based on the 1987 study, at least in terms of the traps, according to Moreno. 

These cicada traps were conical and made of wire with window mesh. Modifications were made to ensure that once a cicada was trapped, it could not escape. 

One site used was Hueston Woods State Park, which is, according to Moreno, one of the few remaining relics of old-growth forests in Ohio. 

Moreno explained that his 2021 study focused on Brood 10, or Brood X. 

Going into the study, Moreno and his student counted the number of holes in the ground and assumed that from each hole, at least one cicada emerged. This allows scientists, like Moreno and his student, to know how many cicadas emerged in each brood.

“If we see more holes, then that means that there are more cicadas,” he said. “If there are less holes, then that means the cicadas aren’t doing as great as before.”

Moreno used the study to determine what time of year the brood emerged, or came out of the ground first.

Each cicada was studied by hand. By looking at the insect’s abdomen and using other precise techniques, Moreno deciphered which one of three species they were studying and if the cicadas were male or female.

If male cicadas come out early and before the females, they live only two weeks. This limits the amount of time these cicadas have to mate.

Another important aspect of the study was finding how much the temperature had changed since the last study.

“The cicadas depend on the temperature, like a cue they receive, to come out of the ground,” said Moreno. 

According to Moreno, they were able to conclude that the old growth forests, like those in Hueston Woods State Park, seem to have some declining trends.

Moreno found that such areas have lost populations over the course of the past three generations studied.

“Two to three woodlots also show declines (in cicada populations,)” said Moreno. Study findings also reflected that these rural woodlots tended to have very moist soil in comparison to the other areas studied. 

“On the other hand,” he said, “we had the fencerows, these very thin strips of trees in the middle of farmlands, which had a huge increase.”

Moreno noted that this increase was from 100 to 400 cicadas in a single square meter. 

“These fencerows are a very important habitat for cicadas,” said Moreno.

He believes that if farmers and land owners replace these fencerows for a metal or wire fence, populations of cicadas could decline. 

Moreno expressed concern for future cicada generations.

“My worry is the following scenario: Imagine in 13 years from now (2038) when the next Brood X emergence would happen, if we see less, or none, cicadas appear in some regions,” he said. “To just vanish, as it happened with Brood XI in the 50s, and as it is happening with many other insect species across the world, we may see more discussions on ‘what could have we done to protect them?’” 

The full study about these cicadas can be found on the Ecological Society of America website.