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Tropical species are moving northward in U.S. as winters warm: Insects, reptiles, fish and plants migrating north as winter freezes in South become less frequent

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Tropical species are moving northward in U.S. as winters warm: Insects, reptiles, fish and plants migrating north as winter freezes in South become less frequent

Notwithstanding last month’s cold snap in Texas and Louisiana, climate change is leading to warmer winter weather throughout the southern U.S., creating a golden opportunity for many tropical plants and animals to move north, according to a new study appearing this week in the journal Global Change Biology.

Some of these species may be welcomed, such as sea turtles and the Florida manatee, which are expanding their ranges northward along the Atlantic Coast. Others, like the invasive Burmese python — in the Florida Everglades, the largest measured 18 feet, end-to-end — maybe less so.Equally unwelcome, and among the quickest to spread into warming areas, are the insects, including mosquitoes that carry diseases such as West Nile virus, Zika, dengue and yellow fever, and beetles that destroy native trees.”Quite a few mosquito species are expanding northward, as well as a lot of forestry pests: bark beetles, the southern mountain pine beetle,” said Caroline Williams, associate professor of integrative biology at the University of California, Berkeley, and a co-author of the paper. “In our study, we were really focusing on that boundary in the U.S. where we get that quick tropical-temperate transition. Changes in winter conditions are one of the major, if not the major, drivers of shifting distributions.”That transition zone, northward of which freezes occur every winter, has always been a barrier to species that evolved in more stable temperatures, said Williams, who specializes in insect metabolism — in particular, how winter freezes and snow affect the survival of species.

“For the vast majority of organisms, if they freeze, they die,” she said. “”Cold snaps like the recent one in Texas might not happen for 30 or 50 or even 100 years, and then you see these widespread mortality events where tropical species that have been creeping northward are suddenly knocked back. But as the return times become longer and longer for these extreme cold events, it enables tropical species to get more and more of a foothold, and even maybe for populations to adapt in situ to allow them to tolerate more cold extremes in the future.””

The study, conducted by a team of 16 scientists led by the U.S. Geological Survey (USGS), focused on the effects warming winters will have on the movement of a broad range of cold-sensitive tropical plants and animals into the Southern U.S., especially into the eight subtropical U.S. mainland states: Florida, Alabama, Mississippi, Louisiana, Texas, New Mexico, Arizona and California. Williams and Katie Marshall of the University of British Columbia in Vancouver co-wrote the section on insects for the study.The team found that a number of tropical species, including insects, fish, reptiles, amphibians, mammals, grasses, shrubs and trees, are enlarging their ranges to the north. Among them are species native to the U.S., such as mangroves, which are tropical salt-tolerant trees; and snook, a warm water coastal sport fish; and invasive species such as Burmese pythons, Cuban tree frogs, Brazilian pepper trees and buffelgrass.

“”We don’t expect it to be a continuous process,” said USGS research ecologist Michael Osland, the study’s lead author. “There’s going to be northward expansion, then contraction with extreme cold events, like the one that just occurred in Texas, and then movement again. But by the end of this century, we are expecting tropicalization to occur.”

The authors document several decades’ worth of changes in the frequency and intensity of extreme cold snaps in San Francisco, Tucson, New Orleans and Tampa — all cities with temperature records stretching back to at least 1948. In each city, they found, mean winter temperatures have risen over time, winter’s coldest temperatures have gotten warmer, and there are fewer days each winter when the mercury falls below freezing.

Temperature records from San Francisco International Airport, for example, show that before 1980, each winter would typically see several sub-freezing days. For the past 20 years, there has been only one day with sub-freezing temperatures.

Changes already underway or anticipated in the home ranges of 22 plant and animal species from California to Florida include:

  • Continuing displacement of temperate salt marsh plants by cold-sensitive mangrove forests along the Gulf and southern Atlantic coasts. While this encroachment has been happening over the last 30 years, with sea-level rise, mangroves may also move inland, displacing temperate and freshwater forests.
  • Buffelgrass and other annual grasses moving into Southwestern deserts, fueling wildfire in native plant communities that have not evolved in conjunction with frequent fire.
  • The likelihood that tropical mosquitos that can transmit encephalitis, West Nile virus and other diseases will further expand their ranges, putting millions of people and wildlife species at risk of these diseases.
  • Probable northward movement, with warming winters, of the southern pine beetle, a pest that can damage commercially valuable pine forests in the Southeast.
  • Recreational and commercial fisheries’ disruption by changing migration patterns and the northward movement of coastal fishes.

The changes are expected to result in some temperate zone plant and animal communities found today across the southern U.S. being replaced by tropical communities.

“”Unfortunately, the general story is that the species that are going to do really well are the more generalist species — their host plants or food sources are quite varied or widely distributed, and they have relatively wide thermal tolerance, so they can tolerate a wide range of conditions,” Williams said. “And, by definition, these tend to be the pest species — that is why they are pests: They are adaptable, widespread and relatively unbothered by changes in conditions, whereas, the more specialized or boutique species are tending to decline as they get displaced from their relatively narrow niche.”

She cautioned that insect populations overall are falling worldwide.

“We are seeing an alarming decrease in total numbers in natural areas, managed areas, national parks, tropical rain forests — globally,” she said. ” So, although we are seeing some widespread pest species increasing, the overall pattern is that insects are declining extremely rapidly.”

The authors suggest in-depth laboratory studies to learn how tropical species can adapt to extreme conditions and modeling to show how lengthening intervals between cold snaps will affect plant and animal communities.

“”On a hopeful note, it is not that we are heading for extinction of absolutely everything, but we need to prepare for widespread shifts in the distribution of biodiversity as climate, including winter climate, changes,” Williams said. “”The actions that we take over the next 20 years are going to be critical in determining our trajectory. In addition to obvious shifts, like reducing our carbon footprint, we need to protect and restore habitat for insects. Individuals can create habitat in their own backyards for insects by cultivating native plants that support pollinators and other native insects. Those are little things that people can do and that can be important in providing corridors for species to move through our very fragmented habitats.””

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The unintended consequences of success against malaria

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Tropical species are moving northward in U.S. as winters warm: Insects, reptiles, fish and plants migrating north as winter freezes in South become less frequent


For decades, insecticide-treated bed nets and indoor insecticide spraying regimens have been important — and widely successful — treatments against mosquitoes that transmit malaria, a dangerous global disease. Yet these treatments also — for a time — suppressed undesirable household insects like bed bugs, cockroaches and flies.

Now, a new North Carolina State University study reviewing the academic literature on indoor pest control shows that as the household insects developed resistance to the insecticides targeting mosquitoes, the return of these bed bugs, cockroaches and flies into homes has led to community distrust and often abandonment of these treatments — and to rising rates of malaria.

In short, the bed nets and insecticide treatments that were so effective in preventing mosquito bites — and therefore malaria — are increasingly viewed as the causes of household pest resurgence.

“These insecticide-treated bed nets were not intended to kill household pests like bed bugs, but they were really good at it,” said Chris Hayes, an NC State Ph.D. student and co-corresponding author of a paper describing the work. “It’s what people really liked, but the insecticides are not working as effectively on household pests anymore.”

“Non-target effects are usually harmful, but in this case they were beneficial,” said Coby Schal, Blanton J. Whitmire Distinguished Professor of Entomology at NC State and co-corresponding author of the paper.

“The value to people wasn’t necessarily in reducing malaria, but was in killing other pests,” Hayes added. “There’s probably a link between use of these nets and widespread insecticide resistance in these house pests, at least in Africa.”

The researchers add that other factors — famine, war, the rural/city divide, and population displacement, for example — also could contribute to rising rates of malaria.

To produce the review, Hayes combed through the academic literature to find research on indoor pests like bed bugs, cockroaches and fleas, as well as papers on malaria, bed nets, pesticides and indoor pest control. The search yielded more than 1,200 papers, which, after an exhaustive review process, was whittled down to a final count of 28 peer-reviewed papers fulfilling the necessary criteria.

One paper — a 2022 survey of 1,000 households in Botswana — found that while 58% were most concerned with mosquitoes in homes, more than 40% were most concerned with cockroaches and flies.

Hayes said a recent paper — published after this NC State review was concluded — showed that people blamed the presence of bed bugs on bed nets.

“There is some evidence that people stop using bed nets when they don’t control pests,” Hayes said.

The researchers say that all hope is not lost, though.

“There are, ideally, two routes,” Schal said. “One would be a two-pronged approach with both mosquito treatment and a separate urban pest management treatment that targets pests. The other would be the discovery of new malaria-control tools that also target these household pests at the same time. For example, the bottom portion of a bed net could be a different chemistry that targets cockroaches and bed bugs.

“If you offer something in bed nets that suppresses pests, you might reduce the vilification of bed nets.”

The study appears in Proceedings of the Royal Society B. The review was supported in part by the Blanton J. Whitmire Endowment at NC State, and grants from the U.S. Department of Housing and Urban Development Healthy Homes program (NCHHU0053-19), the Department of the Army, U.S. Army Contracting Command, Aberdeen Proving Ground, Natick Contracting Division, Ft. Detrick, Maryland (W911QY1910011), and the Triangle Center for Evolutionary Medicine (257367).



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Drawing water from dry air

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Tropical species are moving northward in U.S. as winters warm: Insects, reptiles, fish and plants migrating north as winter freezes in South become less frequent


Earth’s atmosphere holds an ocean of water, enough liquid to fill Utah’s Great Salt Lake 800 times.

Extracting some of that moisture is seen as a potential way to provide clean drinking water to billions of people globally who face chronic shortages.

Existing technologies for atmospheric water harvesting (AWH) are saddled with numerous downsides associated with size, cost and efficiency. But new research from University of Utah engineering researchers has yielded insights that could improve efficiencies and bring the world one step closer to tapping the air as a culinary water source in arid places.

The study unveils the first-of-its-kind compact rapid cycling fuel-fired AWH device. This two-step prototype relies on adsorbent materials that draw water molecules out of non-humid air, then applies heat to release those molecules into liquid form, according to Sameer Rao, senior author of the study published Monday and an assistant professor of mechanical engineering.

“Hygroscopic materials intrinsically have affinity to water. They soak up water wherever you go. One of the best examples is the stuff inside diapers,” said Rao, who happens to be the father of an infant son. “We work with a specific type of hygroscopic material called a metal organic framework.”

Rao likened metal organic frameworks to Lego blocks, which can be rearranged to build all sorts of structures. It this case they are arranged to create a molecule ideal for gas separation.

“They can make it specific to adsorb water vapor from the air and nothing else. They’re really selective,” Rao said. Developed with graduate student Nathan Ortiz, the study’s lead author, this prototype uses aluminum fumarate that was fashioned into panels that collect the water as air is drawn through.

“The water molecules themselves get trapped on the surfaces of our material, and that’s a reversible process. And so instead of becoming ingrained into the material itself, it sits on the walls,” Ortiz said. “What’s special about these absorbent materials is they have just an immense amount of internal surface area. There’s so many sites for water molecules to get stuck.”

Just a gram of this material holds as much surface area as two football fields, according to Rao. So just a little material can capture a lot of water.

“All of this surface area is at the molecular scale,” Rao said. “And that’s awesome for us because we want to trap water vapor onto that surface area within the pores of this material.”

Funding for the research came from the DEVCOM Soldier Center, a program run by the Department of Defense to facilitate technology transfer that supports Army modernization. The Army’s interest in the project stems from the need to keep soldiers hydrated while operating in remote areas with few water sources.

“We specifically looked at this for defense applications so that soldiers have a small compact water generation unit and don’t need to lug around a large canteen filled with water,” Rao said. “This would literally produce water on demand.”

Rao and Ortiz have filed for a preliminary patent based on the technology, which addresses non-military needs as well.

“As we were designing the system, I think we also had perspective of the broader water problem. It’s not just a defense issue, it’s very much a civilian issue,” Rao said. “We think in terms water consumption of a household for drinking water per day. That’s about 15 to 20 liters per day.”

In this proof of concept, the prototype achieved its target of producing 5 liters of water per day per kilogram of adsorbent material. In a matter of three days in the field, this devise would outperform packing water, according to Ortiz.

In the device’s second step, the water is precipitated into liquid by applying heat using a standard-issue Army camping stove. This works because of the exothermic nature of its water collecting process.

“As it collects water, it’s releasing little bits of heat. And then to reverse that, we add heat,” Ortiz said. “We just put a flame right under here, anything to get this temperature up. And then as we increase the temperature, we rapidly release the water molecules. Once we have a really humid airstream, that makes condensation at ambient temperature much easier.”

Nascent technologies abound for atmospheric water harvesting, which is more easily accomplished when the air is humid, but none has resulted in equipment that can be put to practical use in arid environments. Ortiz believes his device can be the first, mainly because it is powered with energy-dense fuel like the white gasoline used in camping stoves.

The team decided against using photovoltaics.

“If you’re reliant on solar panels, you’re limited to daytime operation or you need batteries, which is just more weight. You keep stacking challenges. It just takes up so much space,” Ortiz said. “This technology is superior in arid conditions, while refrigeration is best in high humidity.”



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3D-printed microstructure forest facilitates solar steam generator desalination

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Tropical species are moving northward in U.S. as winters warm: Insects, reptiles, fish and plants migrating north as winter freezes in South become less frequent


Faced with the world’s impending freshwater scarcity, a team of researchers in Singapore turned to solar steam generators (SSGs), which are emerging as a promising device for seawater desalination. Desalination can be a costly, energy-intensive solution to water scarcity. This renewable-powered approach mimics the natural water cycle by using the sun’s energy to evaporate and isolate water. However, the technology is limited by the need to fabricate complex topologies to increase the surface area necessary to achieve high water evaporation efficiency.

To overcome this barrier, the team sought design inspiration from trees and harnessed the potential of 3D printing. In Applied Physics Reviews, the team presents a state-of-the-art technology for producing efficient SSGs for desalination and introduces a novel method for printing functional nanocomposites for multi-jet fusion (MJF).

“We created SSGs with exceptional photothermal performance and self-cleaning properties,” said Kun Zhou, a professor of mechanical engineering at Nanyang Technological University. “Using a treelike porous structure significantly enhances water evaporation rates and ensures continuous operation by preventing salt accumulation — its performance remains relatively stable even after prolonged testing.”

The physics behind their approach involves light-to-thermal energy conversion, where the SSGs absorb solar energy, convert it to heat, and evaporate the water/seawater. The SSG’s porous structure helps improve self-cleaning by removing accumulated salt to ensure sustained desalination performance.

“By using an effective photothermal fusing agent, MJF printing technology can rapidly create parts with intricate designs,” he said. “To improve the photothermal conversion efficiency of fusing agents and printed parts, we developed a novel type of fusing agent derived from metal-organic frameworks.”

Their SSGs were inspired by plant transpiration and are composed of miniature tree-shaped microstructures, forming an efficient, heat-distributing forest.

“Our bioinspired design increases the surface area of the SSG,” said Zhou. “Using a treelike design increases the surface area of the SSG, which enhances the water transport and boosts evaporation efficiency.”

One big surprise was the high rate of water evaporation observed in both simulated environments and field trials. The desalinated water consistently met standards for drinking water — even after a long-time test.

“This demonstrates the practicality and efficiency of our approach,” Zhou said. “And it can be quickly and easily mass-produced via MJF commercial printers.”

The team’s work shows significant potential for addressing freshwater scarcity.

“Our SSGs can be used in regions with limited access to freshwater to provide a sustainable and efficient desalination solution,” said Zhou. “Beyond desalination, it can be adapted for other applications that require efficient solar energy conversion and water purification.”



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