As much of the world prepares for hotter and drier growing seasons as the result of climate change, a research team led by University of Nevada, Reno researchers has identified several varieties of cactus pear that are particularly well-suited to producing biomass for fuels production.

The new findings build on earlier research led by John Cushman, a professor in the University’s Department of Biochemistry & Molecular Biology in the College of Agriculture, Biotechnology & Natural Resources. The earlier work identified the cactus pear as a climate-resilient, water-efficient and highly productive source of biomass for fuels production.

Now, research published in the Journal of Agronomy and Crop Science tracks the result of a three-year field trial of 14 varieties of cactus pear grown under semi-arid conditions at the National Arid Land Plant Genetics Resources Unit near Fresno, Calif. The test compared the amount of biomass produced by each of the 14 varieties.

Dramatic differences between varieties

Cushman, the primary investigator on the most recent research who also conducts research as part of the College’s Experiment Station unit, said the tests discovered surprising variation in biomass production among the varieties. The best producing variety, in fact, performed eight times better than the poorest producing variety. Researchers also found significant differences in the ease of vegetative propagation.

The variety that consistently produced the most biomass in the new test is a hybrid that’s a cross between a species of wild prickly pear native to Texas and a spineless variety developed by Peter Felker at Texas A&M University for use by commercial growers.

That same hybrid produced the most cladodes, the elongated stems that are often mistakenly referred to as cactus leaves, and posted one of the best survival rates over the three-year trial. It also appears to be relatively easy to propagate, helping to reduce the labor costs of replacing plants that die.

Cushman said the outstanding performance of that hybrid variety might be improved even further as plant breeders work to create elite strains.

The 14 varieties of pear cactus in the recent study, including wild and hybrid strains from the United States, Mexico and Brazil, were selected from the nearly 292 possibilities that are grown in greenhouses at the Experiment Station’s Valley Road Field Lab in Reno or in field conditions at the trial site near Fresno.

Water-efficient source of biofuel

The research affirmed earlier findings that cactus pear is highly water-efficient, requiring much less water to produce the same amount of biomass produced by thirstier crops.

“This is a critical factor, as we know that the western United States has limited water supplies that are only becoming more limited with the current global climate crisis,” Cushman said. “So, we should be exploring more water-use efficient crops for our food, feed and bioenergy needs.”

Already, cactus pear is used as animal fodder, fuel and human food—notably, the nopalitos, or green pads of the cactus, that are a mainstay of Mexican cuisine. The fruit, or “tuna,” is also used to make syrups, candies and jellies. Now, Cushman said climate change is spurring even more interest in use of cactus pear as a crop in semi-arid and arid regions.

Known scientifically as Opuntia ficus-indica or Opuntia cochenillifera, cactus pear relies on an unusual type of photosynthesis called crassulacean acid metabolism to stay alive in hot, arid climates. The pores that allow the plant to take in carbon dioxide for photosynthesis close during the heat of the day to preserve moisture inside, then open during the cooler evening and nighttime hours.

Next: Studies of pests, optimal fertilizers

Dhurba Neupane, previously a post-doctoral researcher in the University’s Department of Biochemistry & Molecular Biology and the lead author of the recent paper, has been studying biofuels for more than 14 years. Neupane, who now works as a research agronomist at the North Central Agricultural Research Laboratory in Brookings, S.D., said previous studies found that cactus pear can be combined with wastes such as cow manure or slaughterhouse waste to produce climate-friendly biofuels.

But while the newest tests confirmed the potential of a hybrid form of pear cactus for efficient production of biomass, Neupane said researchers still want to learn more about a disease that can stunt the growth of the cactus, as well as the threat posed by the cochineal scale insect that feeds on pear cactus.

Cushman said the next steps for researchers will include tests of the best levels of fertilization to improve production while avoiding overfertilization and tests of planting density. Scientists want to learn more, too, about the adaptability of pear cactus across different growing regions of the American South and Southwest.

Cushman said researchers have described cactus pear as a “future food.”

“We need to explore more climate-resilient crops if we are to be able to provide for the future food, forage and fodder, and biofuel needs of a growing human population,” he said. “Cactus pear is an extremely important and versatile crop that deserves greater attention.”

In 2003, Anne Nielsen became the first doctoral student in the U.S. to study the brown marmorated stink bug, which was beginning its ascendancy as an invasive species notoriously damaging to crops.

Working with her mentor, Rutgers entomologist George Hamilton, Nielsen traced the stink bug’s life cycle and origins. By the time the stink bug populations exploded in 2009–2010, Nielsen and Hamilton were in a unique position to advise farmers on countermeasures.

Now an associate professor in the Department of Entomology in the Rutgers School of Environmental and Biological Sciences (SEBS), Nielsen is also an Extension Specialist in tree fruit, with a special focus on invasive species like stink bugs and spotted lanternflies and their effects on fruit crops. Her goal is to protect the natural world by developing sustainable management practices.

After a morning spent with students in a peach orchard at the Rutgers Agriculture Research and Extension Center in Bridgeton, N.J., Nielsen discussed the threat of invasive species and the continuing effort to contain them.

What are invasive species?

An invasive species is a non-native species that is causing economic or ecological harm. They are more than just minor annoyances. They can cause major economic damage each year.

Invasive species are not going away. They are part of our lives because the world is so connected now. It’s something we need to continue to confront because it’s going to keep happening.

You just spent hours in a peach orchard with your students. What were you studying?

I’m out there looking at the whole system, the ecological environment. We look at the fruit trees, the grass underneath and the woods surrounding the orchard, and think about the natural enemies present. We take the whole picture into account and fit puzzle pieces together.

We study the biology of invasive insects so that we can figure out when they’re present and identify the correct timings for management. We also look at their behavior.

We’ve done a lot of work looking at how they move across the surrounding landscape and within an orchard, and then we can exploit that behavior for management. We’ve found what we call border spray techniques, so we can reduce the amount of area in the orchard that is sprayed with pesticides. This is part of the strategy we are developing to incorporate biological techniques that are more environmentally friendly.

You are engaged in an ongoing battle against invasive species. What are the stakes?

New Jersey is the Garden State; agriculture is at the heart of who we are. These invasive species come in and they change our production practices, how we view agriculture and insects. Insects get vilified. We must balance our management of invasive insects with consumer demands for clean fruit and less pesticides.

Peach crops, and fruit crops in general, can be destroyed by invasive species. New Jersey is the number four growing region for peaches in the country. At the height of the marmorated stink bug infestation from 2010 to 2011, we lost 60 percent of our peach crops.

We also have a lot of apple orchards and wine vineyards that are vulnerable to these pests, as well as farms with equally imperiled small fruits like blueberries and raspberries. These crops are tied to a lot of people’s livelihoods and provide great economic value to the state.

When we think of economic loss from invasive insects, we see there are multiple factors driving that phenomenon, including some that incur hidden costs. There’s an invasive fruit fly called spotted wing drosophila that is a major pest of small fruit like blueberries and raspberries.

I know growers who have pulled up all their raspberry plants. One wine grape grower handpicks stink bugs out of the grapes on the processing line before crushing the grapes to maintain high quality wines.

How do invasive species get here?

There are a lot of different routes of introduction for an invasive species. The most common one that we see is associated with shipping containers and global trade. We have a lot of ports of entry in this region. New Jersey and most of the mid-Atlantic are so densely populated that farms are often near urban areas, forming what we call the agro-urban interface, increasing the odds of invasive species reaching crop areas.

When you refer to achieving a balance in nature, what do you mean?

We had been looking at marmorated stink bugs for some time before they reached outbreak levels. We had a couple of bad years and then the populations naturally declined. A lot of invasive species exhibit these boom-and-bust cycles in their populations. Several factors come together—the environment starts pushing back, scientists develop new methods—and we’re able to reduce the population.

What sort of natural controls are evolving for the brown marmorated stink bug?

A lot of our focus now is on biological control of the stink bug using a parasitoid species—a tiny stingless wasp about the size of a poppy seed. They lay their eggs inside stink bug eggs. When those eggs hatch, they destroy the stink bug eggs. This has the potential to help control populations over time in a more sustainable manner.

We have done a few small releases of the wasps with farmers in New Jersey and at the Rutgers research station. We’re still working out the method’s biological impact.

How did you get involved in spotted lanternfly research?

The lanternfly was first detected in New Jersey in 2018 and in Pennsylvania a few years before that. Most of the explosive growth of the lanternfly coincided with the pandemic.

We studied it in Pennsylvania early on, learning how to identify it, and understand what trees it liked. In 2019, we started receiving significant reports from farmers in New Jersey about infestations in wine grapes.

In collaboration with Julie Lockwood, [a professor in the Department of Ecology, Evolution and Natural Resources at SEBS], we devised a method identifying lanternflies through genetic signatures. We were able to combine this detection method to inform our growers during the pandemic and reducing pesticide use by figuring out the best materials to use and the best times to spray. And we’re still battling them.

We are actively looking for biological control approaches to limit the lanternfly population and have found a few candidates. But we are still figuring this out.

Inside a hallway of the veterinary hospital at the Maryland Zoo in Baltimore, a popular new program plays 24/7 on a computer screen.

They call it “Woodrat TV,” said Erin Grimm, the zoo’s mammal curator.

On camera is a singularly important Allegheny woodrat, whose job it is to help repopulate her species, which is threatened by encroachment from human development. She is the first participant in a captive breeding program at the zoo to save the woodrat, a big-eared relative of the pack rat that’s about the length of a bowling pin (if you include the woodrat’s furry tail).

When she arrived at the zoo from her habitat in Pennsylvania, Allegheny Woodrat 9891, as she is known, was already pregnant. Within weeks, she gave birth to three healthy pups: Must See TV on the Woodrat Channel.

Woodrats are solitary critters who live in remote, rocky outcroppings dotting the Appalachians from Pennsylvania to Georgia, hidden from all but the most determined seekers. Several biologists have watched the zoo’s footage eagerly, Grimm said, having never seen a woodrat give birth before, despite years of studying and tracking them.

“They are secretive and live in tiny cracks and crevices in the rocks,” Grimm said. “It’s nice for us to be able to capture this.”

But, for the zoo’s program, that’s just a cherry on top. The real goal lies with those three rapidly growing woodrats, who will be released into the wild in Pennsylvania and Indiana. The juvenile woodrats will offer something desperately needed in their new homes: genetic diversity.

Underlying the woodrats’ precipitous decline is, unsurprisingly, human development. The construction of homes, buildings and roads has isolated individual populations of woodrats, destroying the forested lands through which they traveled to breed with one another.

Scientists call it the “extinction vortex,” said Jacqueline Doyle, a Towson University associate professor who studies the genetics of woodrat populations. As animals are assailed by habitat loss, pollution, hunting or invasive species, their populations shrink and fragment—and so does the gene pool.

Inbreeding and the loss of genetic diversity make entire populations less adaptable to disease and environmental change, and can send species into a tailspin.

“Even if you address the initial problem that resulted in the population decreasing in size—even if you combat habitat loss or you combat an exotic species—if you’ve lost that genetic variation, it can still be very difficult for the population to recover,” Doyle said.

Doyle is assisting with the captive breeding program, which is being administered through a special work group dedicated to the creatures. By comparing DNA samples collected from the baby woodrats, and samples collected in the wild, Doyle will help play matchmaker, by identifying the woodrat populations most in need of the pups’ unique genetic background.

But at the beginning of their lives at the Maryland Zoo, these potential species-savers were just like any other kids. As soon as the lights went off each night and the cameras switched to infrared, the nocturnal “rat chaos” would begin, Grimm said. The siblings often sparred with one another, rising to stand on their back feet and box with their paws. That is, until Mom separated them.

The woodrats grew in a multilayer cage with PVC piping for tunnels. And that cage was locked behind latched, lion-proof metal doors, since it sits inside a room previously used to treat the zoo’s other, much larger, inhabitants. Now, a whiteboard hangs out front, with a drawing of a rat and the words “Rat Room.”

After Mom and the kids spent several weeks together, zoo staff separated them. Now, each woodrat has its own enclosure. Zoo staff are keeping their distance, trying to ensure that the young woodrats don’t grow too accustomed to humans, or hearing human voices.

Soon, the woodrats will go to the wild, where they will spend their first two weeks in an enclosed area with natural food items. Then, the gates will open, and eventually the enclosure will be removed, leaving them on their own.

The zoo employees weren’t sure how Mom would react to losing her young. But mostly, she just seemed to take some much-needed R&R, sleeping in her nest assembled partially from her favorite nesting material—toilet paper—and munching on the chinchilla chow, seeds, nuts and fresh produce that arrive through a chute.

Along the way, the zoo is picking up meaningful tidbits about woodrat behavior that will help other zoos that are discussing how to replicate the program, Grimm said.

For the Maryland Zoo, the breeding program isn’t atypical, said spokesman Mike Evitts. The zoo participates in similar programs for the African penguin and the Panamanian golden frog. Such programs are a bit more rare for mammals that are difficult to breed, Grimm said, though the zoo had a brief breeding program for woodrats decades ago.

Perhaps the program’s biggest challenges lie ahead: ensuring that the baby woodrats survive in the wild, and successfully mating Woodrat 9891 in captivity, said Kate Otterbein, a mammal recovery specialist at the Pennsylvania Game Commission, who trapped Woodrat 9891 in central Pennsylvania’s Mifflin County and drove her to Baltimore.

“It’s not simple as just putting them together, because they’re not social and they are territorial, and they get aggressive when another woodrat is in their territory,” Otterbein said.

Staff members will need to carefully monitor the courting, to ensure it doesn’t sour to the point that one of the woodrats becomes violent, Otterbein said.

The Allegheny woodrat is listed as endangered in Maryland and several other states, and is “near threatened” on a global scale, as measured by the International Union for Conservation of Nature’s Red List.

Woodrats have other environmental factors working against them. Raccoons, for example, pushed by human development, have foraged deeper into the woods, where they are more likely to encounter Allegheny woodrats.

Raccoons can carry a parasite called racoon roundworm, which lies dormant inside them, but is typically lethal when passed to a woodrat. The woodrats’ food sources have also taken a hit, such as chestnut trees destroyed by chestnut blight and acorn-producing oak trees imperiled by the spongy moth.

The Maryland Department of Natural Resources is beginning a statewide reassessment survey of its remaining woodrat populations, said Megan Zagorski, the agency’s western region ecologist. Historically, the creatures could be found in the state’s westernmost four counties and Montgomery County. Over time, the population generally appears to be contracting westward, as sites that formerly hosted woodrats are lost.

Zagorski hopes the holistic survey will provide meaningful answers to explain the decline, but the state’s existing survey work has provided clues, including trail cameras that pick up families of raccoons passing by.

“One of the sites … is one mountain and the next mountain, and in between those two mountains, put a highway,” Zagorski said. “So it’s much more difficult for woodrats to safely cross and mix across that ridge line.”

In addition to the captive breeding program, state officials are trying other methods to keep the critters alive. In Pennsylvania, that comes in the form of taxing work: At key times of the year, state employees and volunteers haul 25-pound bags of chestnuts up into the mountains to drop them in crevices only hungry woodrats could reach, Otterbein said. The state game commission also has worked to rebuild rock areas to connect woodrat habitats, she said.

It’s not just about the woodrats. Their habitats also are used by rattlesnakes, birds of prey, black bears and other small mammals, such as rock moles, Otterbein said.

“I like to think of it as this complex puzzle of species that fit into this community, and the idea of losing some of those pieces of the puzzle is just not something that we want to face,” Otterbein said.

The woodrat also deserves study—and saving—on its own merits, the scientists say. There’s a lot of interest among scientists in working with what they call “charismatic megafauna,” Doyle said. Think polar bears, golden eagles, dolphins.

“The Allegheny woodrat is—perhaps some would argue—less charismatic. It’s certainly not mega,” Doyle said. “But it’s no less important ecologically than these top predators that many people are interested in studying.”

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