Rice is the No. 1 staple food for the world’s poorest and most undernourished people. More than half of the world’s population eats rice every day. In sub-Saharan Africa, rice is the fastest-growing food source, providing more food calories than any other crop. One dangerous threat to food security is the rice disease bacterial blight, caused by the bacterium Xanthomonas oryzae pv. oryzae (Xoo). The annual losses caused by bacterial blight are estimated at U.S. $3.6 billion in India alone. Xoo can destroy a smallholder’s entire annual harvest, putting their food supply, income and land ownership at risk.
Healthy Crops aims to provide these farmers with effective tools to combat bacterial blight and thus eliminate the epidemic in the long term. The consortium is composed of six research institutions on three continents.
So how did the team manage to rein in the bacteria? “We limit the ability of the noxious Xoo bacterium to divide by preventing it from hijacking the plant’s resources as food supply,” explains Dr. Bing Yang from the University of Missouri. To understand this, they used their knowledge of how the Xoo bacteria accesses the host’s nutrients. Once Xoo infects a rice plant, it secretes proteins, the so-called TAL effectors, into the rice cell. TAL effectors turn on the host’s SWEET genes, which then export sugar from the rice cells and make it available to the bacteria, which live in the cell wall space. The bacteria then have enough resources to multiply.
Some rice varieties are resistant against some specific types of Xoo bacteria. The team had previously determined that these varieties contain variants of the SWEET promoter, which do not allow binding of the bacterial TAL effectors. In essence, the plants changed the lock, so the bacteria cannot activate the SWEET transporters and manipulate sugar transport for their own benefit.
In turn, the bacterium can adapt: Different strains of Xoo attack with different keys. There is a race between Xoo strains developing new keys on the one hand, and resistant rice varieties with altered locks on the other. The consortium identified six points of attack in the SWEET promoters. Wolf B. Frommer, the project leader, said, “With the knowledge gained and the tools developed here, we might be at least as fast in developing new resistances as the bacteria can develop new keys.”
In two back-to-back publications in the journal Nature Biotechnology, Healthy Crops present a series of variants collected from all over the world for two popular rice varieties that are resistant to a large collection of Xoo strains that cause bacterial blight disease. It also describes the Sweetr-Resistance Kit that enables rapid characterization of new bacterial strains to devise a rapid and well-targeted deployment strategy of new resistances to defeat the disease also in the long term.. This kit should soon be available to rice growers and researchers in Asia and sub-Saharan Africa.
Dr. Boris Szurek, the team leader from IRD, says, “We used the most advanced tools to get one step ahead of the pathogen in its arm’s race with the rice plant.”
Dr. Ricardo Oliva, who heads the IRRI team, says, “It is an exciting time to work on rice breeding for disease resistance. Our findings pave the way for the eradication of diseases that have severely affected the lives of smallholder farmers who depend on rice for their livelihood. It is now even more possible to outsmart the enemy by being a step ahead of it.”
The western corn rootworm causes economic losses of over 2 billion US dollars in maize cultivation and is thus a serious agricultural pest. Originally from America, the western corn rootworm is currently invading Europe, including Switzerland.
A successful pest
In an earlier study, Christelle Robert and Matthias Erb from the Institute of plant sciences (IPS) at the University of Bern elucidated one of the strategies that underlies the success of the western corn rootworm. Maize plants store certain defense substances, so-called benzoxazinoids, in their roots. These substances are harmful to many pests. However, the western corn rootworm has developed a strategy to detoxify these substances. The larvae of the corn rootworm thus become resistant against the plant’s own defense. Even worse — the larvae store the benzoxazinoids in their bodies and in turn, use them for self-defense against their own enemies, including parasitic roundworms (entomopathogenic nematodes). The fact that the western corn rootworm has found a defense strategy against nematodes is of particular importance, as the nematodes are used as biological control agents against this pest.
“Considerable successes have already been achieved in the field using nematodes; efficiency-increasing measures could further boost this approach,” explains Matthias Erb, Professor for Biotic Interactions at the IPS. “Against this background, we asked ourselves the question: If pests such as the western corn rootworm can become immune against plant defense substances, could beneficial organisms such as entomopathogenic nematodes do the same?”
Breeding beneficial organisms for pest control
The researchers compared nematodes from areas in which the western corn rootworm is present with nematodes from areas where it is absent. “We found that nematodes from infested areas are resistant against benzoxazinoids, unlike nematodes from other areas,” says Xi Zhang, who worked on the project as a PhD student. In the lab, the researchers were able to observe that nematodes which were exposed to the the western corn rootworm became resistant to plant defense substances within just a few generations. “The speed of this adaptation surprised us,” says Zhang.
The results of the study, which was published in the journal PNAS, are particularly relevant for biological pest control. “Beneficial insects like nematodes, which are resistant against plant defense substances, can keep the insect pests that accumulate these substances from the plant at bay,” explains study co-author Ricardo Machado. This trait can be acquired very quickly through targeted selection and is thus a promising breeding target. “We expect that many other beneficial organisms could be improved by focusing on their capacity to resist plant defense compounds,” says Machado.
In the next stage, researchers are targeting the symbiotic bacteria of the nematodes to make them resistant against benzoxazinoids, and to test the improved biological control agents in the field. “This is a next step to bring our research closer to agricultural application,” says Machado.
Plant defense compounds shape food chains
In the research project, funded by the Swiss National Science Foundation (SNSF), the researchers relied on a combined approach of behavioral ecology, analytical chemistry and plant genetics. The findings illustrate the importance of plant defense compounds such as benzoxazinoids for the evolution and dynamics of food chains. “The arms race between plants and herbivores is often viewed as a motor of the chemical and biological diversity of these two groups,” says study co-author Christelle Robert. “Our study indicates that plant defense compounds may influence the evolution of entire food chains.”
As part of the interfaculty research cooperation “One Health” at the University of Bern (see box), the researchers have recently started to investigate how benzoxazinoids affect the health of animals and humans. “The integration of our findings into the central agricultural food chain is a fascinating expansion of our work with a lot of potential,” says Matthias Erb.
After a challenging 2019, four specific weeds should be on every farmer’s radar for 2020: waterhemp, Palmer amaranth, giant ragweed, and marestail.
Waterhemp and Palmer amaranth
In terms of waterhemp, there was significant seed production potential in 2019.
“I have seen an increase in waterhemp in 2019, especially with all the prevent plant acres, and that is going to mean big problems for some farmers in 2020,” said Kenny Schilling, retail market manager for FMC Corporation. “If you know you are going to have waterhemp issues in the 2020 soybean crop, a farmer needs to plan on using a dicamba or Liberty soybean in that field.
“It is recommended to use a Group 14 and Group 15 Family herbicide in the pre-emerge application and follow it up with a Group 15 Family herbicide again in the post-emerge application, combined with the chemistry from the herbicide resistant soybean that was planted. Most farmers are using either a Group 14 or Group 15, but they really need to use a herbicide from both groups.”
Farmers need to catch waterhemp early.
“Farmers need to learn to treat the seed, not the weed,” Shilling said. “Ideally we need to stop it before it germinates. Waterhemp will grow 1.25 inches each day after it germinates. To be effective, we really need to get it before it gets to the 6- to 8-inch range. At that point it is just too big, and becomes very difficult to control. There are basically 5 days from the time waterhemp germinates until it is a problem, so an application needs to be made before day 5.”
Don Schneider, business representative for BASF concurs with Shilling’s concern. Schneider wants farmers to assess their waterhemp going to be based on how much seed was produced on the acres that were uncontrolled in 2019?
“This is a real issue that needs to have special attention in 2020 if a farmer finds it spread into their field in 2019. Waterhemp is known for its prolific seed production and having a very small, light seed that can easily be spread by the wind. It is a fast grower, and it produces seed throughout the summer,” Schneider said.
Schneider recommends that if a farmer has waterhemp that went to seed, they should plan to go after it with an early spring burndown application or early post-emerge application.
“The farmer will need to have their weapons fully loaded to tackle this weed in 2020,” Schneider said.
Schilling recommends herbicide resistant soybeans when battling tough weeds.
“Farmers should plan on planting a dicamba bean if they know they have a problem. If they have concerns about the risk of the dicamba products, then a Liberty resistant soybean or an Enlist bean (resistant to 2,4-D or glyphosate), and Liberty (glufosinate) should be selected to give the most options for in season control.”
Waterhemp is similar to Palmer amaranth in that it is a prolific seed producer. One Palmer amaranth plant is capable of producing 250,000 to 500,000 seeds. It also germinates the entire growing season from early May until mid-August.
“Farmers really need to layer another residual with the post emerge pass for control of these weeds,” Schneider said.
Neil Badenhop, sales representative for Valent USA, is concerned that waterhemp may have gotten established and gone to seed in either unplanted or untreated fields this past summer. The farmers may not realize the potential problem they have on their hands.
“Proper identification of the weed problem is the first step. Farmers may misidentify waterhemp, thinking it is common lambsquarters,” Badenhop said. “The two weeds look very similar if you do not know what you’re looking for.”
Not all residual herbicides are created equal. A farmer needs to study the Ohio, Indiana and Illinois Weed Control Guide, and evaluate differences in residual herbicides. Different herbicides work better on different weed complexes. Farmers need to purchase an effective herbicide based on individual weed populations.
Some farmers may be lulled into a false sense of security with their “standard” chemistry program. Along with waterhemp, giant ragweed has become a greater concern and creates real challenges in management, Shilling said.
“The problem is if a farmer has both waterhemp and giant ragweed issues, the products that are good on waterhemp are not as good on giant ragweed,” Shilling said. “If there are giant ragweed concerns, a farmer should look at products in the Group 2 Family that contain First Rate or Classic.”
Schneider feels that to effectively battle giant ragweed, both a pre-emerge and post-emerge application strategy are necessary.
“Giant ragweed has a large seed and has a later germination than other weeds, so it causes issues for a pre-emerge application alone without a good post-emerge application to follow-up. Liberty and Engenia are both good options to add to either a pre- or post- application on the respective traited soybeans, and they are both also good on marestail,” Schneider said.
Glyphosate resistant marestail continues to be a problem in fields that have not seen an adjustment in the herbicide program to address the issue.
For farmers with multiple herbicide resistant weed species present, a dicamba resistant soybean is recommended. Dicamba-resistant soybeans, regardless of the company and specific product (Engenia, Xtendimax and FeXapan) are labeled to have the product applied either pre-plant, pre-emerge, or post-emerge. The chemistries have been formulated to reduce the volatility and risk of inversion and off-site movement.
Badenhop has been very impressed with the reformulations and less volatility now compared to his prior experience with the original formulation of dicamba and off target movement risk.
“I thought there would be a lot more issues. The new technology has really lowered the vulnerability and risk. The companies have done a great job,” Badenhop said. “Most complaints seem to be a result of a misapplication from the label directions. As a result, more restrictions continue to be placed on the use of the products in other states.”
Valent USA does not have a dicamba product on the market. Engenia is the BASF dicamba product.
Schneider said the companies that manufacture the dicamba product offer required training for farmers intending to apply it in the 2020 growing season.
“The product label requires dicamba training for anyone who will be applying the dicamba product in 2020,” Schneider said. “This is a two-year label approved by the U.S. EPA. Individual states can have additional stipulations. Ohio has elected to stay with the federal label.”
Ohio Field Leader is a project of the Ohio Soybean Council. For more, visit ohiofieldleader.com.
Ateam of researchers led by evolutionary biologist Nick Grishin at the University of Texas Southwestern Medical Center in Dallas has sequenced the genomes of all butterfly species in the US and Canada, according to a preprint published November 4 on bioRxiv.
Grishin’s team collected butterflies in the wild and also worked with museums and butterfly enthusiasts to obtain genetic material from all 845 butterfly species north of Mexico. Once the researchers had sequenced each genome, they constructed an evolutionary tree based on differences in protein-coding genes. The tree was largely in agreement with previous evolutionary groupings, but the team suggested reclassifying 40 butterfly species at the genus level, reports Nature.
They also found that some groups of butterfly species that evolved faster than others may have done so through interactions with other species that helped the butterflies thrive. For example, Polyommatinae, a group of blue butterflies, has a symbiotic relationship with ants, while Pierini, white butterflies, can eat plants that are toxic to other insects. Both of these were among the fastest-evolving butterfly groups.
Most of the new genomes are “draft” genomes that use short DNA sequences. These genomes can be used to infer evolutionary relationships, but they don’t provide enough information for specific studies of individual genes. The team did create more detailed reference genomes, gene databases derived from multiple organisms, for 23 of the species.
Some researchers are calling the study “a landmark in genomics” due to its scope, according to Nature. “It’s a beautiful piece of work, a tour de force, to do all that,” James Mallet, an evolutionary biologist at Harvard University who was not involved with the study, tells Nature.
There’s no place like home: Many insects moving north in response to climate change find they have nowhere to go in Britain’s intensively managed landscapes, according to new research.
Since the 1970s, insects in the warmer half of Britain have been flying, hopping and crawling northwards at an average rate of around five meters per day. Landscapes that were once too cold for them have been warming up, allowing many species to expand their ranges.
However, the new study, led by researchers at the University of York, suggests that expansion rates have been limited by insufficient habitat in the areas that are becoming climatically suitable.
The study analyzed 25 million recorded sightings of 300 different insect species and found there is huge variation in the rates at which they are moving and that not all species are able to keep pace with the warming conditions.
Scientists and conservationists have always assumed that species’ responses to climate change would be limited by habitat, but this is the first study to measure and quantify the effect across a large and diverse set of species.
Lead author of the study, Dr. Phil Platts from the Department of Environment and Geography at the University of York, said: “To become established somewhere new, animals need the right kinds of vegetation, to provide shelter, food and places to breed.
For many of Britain’s insects, the specific resources they need are not abundant enough in the right places to take full advantage of the new climatic conditions.”
The authors of the study found a diversity of responses within each of the different animal groups they looked at. For example:
Roesel’s bush-cricket has tracked the climate north and west using a variety of habitats, including road verges, which when left uncut provide corridors for expansion. Meanwhile, its more specialized cousin, the Bog Bush Cricket, has struggled to expand its range.
Among dragonflies, the Emperor and Migrant Hawker have sped northwards at between 17 and 28 meters per day, while the Scarce Chaser is penned in by unsuitable vegetation and busy or polluted waterways.
Within butterflies, the Comma has spread rapidly across gardens, woodlands, hedgerows, and other habitats, from Yorkshire to Aberdeen in the course of just a few decades. Whereas the Silver-studded Blue remains confined to rare heathland and grassland habitats and is failing to make headway.
The British climate has improved for all of these species, but expansion rates have varied in large part because of differences in habitat availability.
Dr. Platts added: “Britain has warmed by about 1 °C since the 1970s. That might not sound like much, but it’s the difference in average annual temperature between London and Edinburgh. Warmer ecosystems are typically more biodiverse, and so relatively cool regions could gain more species than they lose under this amount of warming, assuming there is habitat for the new arrivals.
“But the pace of change is fast, and with another degree of warming comes far higher risk of extreme weather, including more heatwaves, droughts, and deluge. Even at one degree, species are already on the move, and so we need to allow for this dynamism in our approach to nature conservation.”
Richard Fox, an author of the study and Associate Director of Recording and Research at Butterfly Conservation said: “Over 25 million sightings of insects were used for this study, the vast majority contributed by ‘citizen scientist’ members of the public. Now it is time for policymakers to create the robust mechanisms, like the Nature Recovery Network in England, that will enable practitioners such as farmers, foresters, conservationists and others to solve our biodiversity crisis.”
Professor Chris Thomas, senior author and Director of the Leverhulme Centre for Anthropocene Biodiversity, said: “As a society we need to do two things: first and foremost, mitigate the pace of change by slashing our carbon emissions. And second, since at least two degrees of warming is more or less inevitable already, we should ensure that habitats are diverse and well-connected, so that our wildlife can track the conditions that suit them best.”
Habitat availability explains variation in climate-driven range shifts across multiple taxonomic groups is published in Scientific Reports.
Reference: “Habitat availability explains variation in climate-driven range shifts across multiple taxonomic groups” by Philip J. Platts, Suzanna C. Mason, Georgina Palmer, Jane K. Hill, Tom H. Oliver, Gary D. Powney, Richard Fox and Chris D. Thomas, 21 October 2019, Scientific Reports. DOI: 10.1038/s41598-019-51582-2
The project was a collaboration between the Universities of York and Reading, Butterfly Conservation, and the Centre for Ecology & Hydrology. The research was funded by the Natural Environment Research Council.
When many people think of watermelon, they likely think of Citrullus lanatus, the cultivated watermelon with sweet, juicy red fruit enjoyed around the world as a dessert. Indeed, watermelon is one of the world’s most popular fruits, second only to tomato—which many consider a vegetable. But there are six other wild species of watermelon, all of which have pale, hard and bitter fruits.
Researchers have now taken a comprehensive look at the genomes of all seven species, creating a resource that could help plant breeders find wild watermelon genes that provide resistance to pests, diseases, drought and other hardships, and further improve fruit quality. Introducing these genes into cultivated watermelon could yield high-quality sweet watermelons that are able to grow in more diverse climates, which will be especially important as climate change increasingly challenges farmers.
“As humans domesticated watermelon over the past 4,000 years, they selected fruit that were red, sweet and less bitter,” said Zhangjun Fei, a faculty member at Boyce Thompson Institute and co-leader of the international effort.
“Unfortunately, as people made watermelons sweeter and redder, the fruit lost some abilities to resist diseases and other types of stresses,” said Fei, who is also an Adjunct Professor in Cornell University’s School of Integrative Plant Science.
As described in a paper published in Nature Genetics on November 1, the researchers made these insights using a two-step process. First, they created an improved version of a “reference genome,” which is used by plant scientists and breeders to find new and interesting versions of genes from their specimens.
“That first reference genome was made using older short-read sequencing technologies,” Fei said. “Using current long-read sequencing technologies, we were able to create a much higher quality genome that will be a much better reference for the watermelon community.”
The group then sequenced the genomes of 414 different watermelons representing all seven species. By comparing these genomes both to the new reference genome and to each other, the researchers were able to determine the evolutionary relationship of the different watermelon species.
“One major discovery from our analysis is that one wild species that is widely used in current breeding programs, C. amarus, is a sister species and not an ancestor as was widely believed,” Fei said.
Indeed, the researchers found that cultivated watermelon was domesticated by breeding out the bitterness and increasing sweetness, fruit size and flesh color. Modern varieties have been further improved in the past few hundred years by increasing sweetness, flavor and crispy texture. The researchers also uncovered regions of the watermelon genome that could be mined to continue improving fruit quality, such as by making them bigger, sweeter and crispier.
In the past 20 to 30 years, plant breeders have crossed cultivated watermelon with the sister species C. amarus and two other wild relatives, C. mucusospermus and C. colocynthis, to make the dessert watermelon more resistant to nematode pests, drought, and diseases like Fusarium wilt and powdery mildew.
These types of improvements using wild relatives is what excites Amnon Levi, a research geneticist and watermelon breeder at that U.S. Department of Agriculture, Agricultural Research Service, U.S. Vegetable Laboratory in Charleston, South Carolina. Levi is a co-author of the paper and provided the genetic material for many of the watermelons used in the study.
“The sweet watermelon has a very narrow genetic base,” says Levi. “But there is wide genetic diversity among the wild species, which gives them great potential to contain genes that provide them tolerance to pests and environmental stresses.”
Levi plans to work with BTI to discover some of these wild genes that could be used to improve the dessert watermelon, especially for disease resistance.
“Watermelon is susceptible to many tropical diseases and pests, whose ranges are expected to continue to expand along with climate change,” says Levi. “We want to see if we can bring back some of these wild disease resistance genes that were lost during domestication.”
Other co-authors included researchers from the Beijing Academy of Agriculture and Forestry Sciences and the Chinese Academy of Agricultural Sciences.
The study was supported in part by funds from the USDA National Institute of Food and Agriculture Specialty Crop Research Initiative (2015-51181-24285), and the US National Science Foundation (IOS-1339287 and IOS-1539831).
In the same issue of Nature Genetics, Fei and colleagues also published a similar paper analyzing 1,175 melons, including cantaloupe and honeydew varieties. The researchers found 208 genomic regions that were associated with fruit mass, quality and morphological characteristics, which could be useful for melon breeding.
Earlier this year, Fei, Levi and colleagues published a reference genome of the ‘Charleston Gray’ watermelon, the principle U.S. variety of C. lanatus to complement the East Asian ‘97103’ genome.
Contrary to the long-held belief that plants in the natural world are always in competition, new research has found that in harsh environments mature plants help smaller ones—and thrive as a result.
The first study to examine plant interactions in a hostile environment over their lifespan found that plants sheltering seedlings help the smaller plant survive and are more successful themselves, a processed in ecology called facilitation.
The study, led by Dr. Rocio Pérez-Barrales at the University of Portsmouth and Dr. Alicia Montesinos-Navarro at Desertification Research Center in Valencia, Spain, studied adult and seedling plants in the ‘ecological desert’ of gypsum soil in the south-east of Spain.
The findings could have significance for those managing harsh environments including coastal management.
Dr. Pérez-Barrales said: “If you’re a seedling in a barren landscape—the top of a mountain or a sand dune, for example—and you’re lucky enough to end up underneath a big plant, your chances of survival are certainly better than if you landed somewhere on your own.
“What we have found which was surprising is an established large plant, called a ‘nurse,’ shields a seedling, it also produces more flowers than the same plants of similar large size growing on their own.”
This win-win for adult and seedling plants in harsh environments has not previously been reported.
“Scientists have often looked at such plant relationships and found an adult or a seedling at one stage of its life, and made conclusions,” Dr. Pérez-Barrales said. “But by studying these plants’ entire lifespan, from seed germination and establishment, growth of young plants, and flowering in adult plants, we have evidence that the benefits for both stack up over time.”
Dr. Pérez-Barrales and her all-female team of scientists studied plant growth in southern Spain over three months during summer. The plants were growing in gypsum, a very poor soil, with little nutrients or water.
They found clear evidence the seedling and nurse were more likely to thrive when grown together, compared to either plant growing alone.
The seedling benefited from shade, more moisture and more nutrients, from the leaf litter of the ‘nurse’ plant, and probably higher bacteria and fungi in the soil, among other things. As it matured, the ‘nurse’ plant grew more flowers than similar plants nearby growing alone, greatly increasing her chances of producing seeds and propagating.
Other benefits of nurse-seedling partnerships include that more variety of plants growing together can trigger a positive cascade effects in the environment. For example, vegetation patches with nurse and facilitated plants with more flower density might be able to attract higher numbers and diversity of pollinators in an area, in turn supporting insect and soil life, and even provide a greater range of different fruit types for birds and mammals.
“The biggest winner for this system of nursing a plant is biodiversity,” Dr. Pérez-Barrales said.
“The more biodiverse an area, the more we have a greater number of species of plants, insect life, bacteria, fungi, mammals and birds, the better the chances are of long-term healthy functioning of the environment and ecosystems.”
The research is likely to be of value to those who manage and protect plants in hostile and harsh environments, such as shingle and sand dunes ecosystems, both of which encircle the UK and are considered at high risk due to human intervention and climate change.
Most home gardeners and arable farmers plan to ensure their soil and conditions are the best they can be for optimum plant growth, but the findings might be of value to those who garden in inhospitable places.
Dr. Pérez-Barrales suggested gardeners experiment with planting different species of different ages together to test which partnerships help plants thrive in any particular location.
More information: Alicia Montesinos-Navarro et al, Benefits for nurse and facilitated plants emerge when interactions are considered along the entire life-span, Perspectives in Plant Ecology, Evolution and Systematics (2019). DOI: 10.1016/j.ppees.2019.125483
Researchers who set out to test the widespread theory that the UK is experiencing an alarming plunge in insect numbers have found no evidence For “insect Armageddon.”
Instead, the researchers from the University of York found peaks and troughs in moth populations over a period of 50 years. They suggest changing weather patterns and climate change could be an explanation.
The study tracked the amount of moths—which the researchers measured by estimating the combined weight, or “biomass” of all moths in a given area—between 1967 and 2017. The findings reveal there is around twice the combined weight of moths in the present day compared with the 1960s.
While there has been a gradual decline in the amount of moths at a rate of around 10 percent per decade since the early 1980s, this came after a steep increase between the late 1960s and 1982.
Lead author of the study, Dr. Callum Macgregor, from the Department of Biology, said: “Moths are a good indicator of what may also be happening in other insect populations as they are the second most diverse group of insect herbivores, with a full range of species from extreme habitat generalists to extreme specialists.
“Our study does not support the narrative that insects are vanishing en masse before our eyes, because there has been a net increase in biomass over the last 50 years. However, the clear decline we observed since the 1980s is still a cause for concern.
“Moths come in all shapes and sizes, so measuring their combined weight allowed us to analyze changes in their populations that are relevant to their predators and food plants.”
Co-author Professor Chris Thomas, from the Department of Biology at the University of York, added: “Biomass is particularly important because it is linked to ecosystem processes, such as the total amount of plant material consumed by insects and food availability for other animals that eat insects.
“Moths provide pollination nocturnally to a wide range of plants, and they provide food for birds, bats and small mammals. Their survival is crucially important to the rest of life on earth.”
The authors investigated the possible reasons behin d the fluctuations in insect populations, and why the results of the study might differ from the conclusions of previous research.
According to the researchers, the use of better and longer-term data may be part of the answer: To put “Insectageddon’ to the test, they analyzed data from “perhaps the best insect population database available anywhere in the world”—the Rothamsted Insect Survey’s national network of light-traps.
The data allowed them to estimate the weight of moths caught each year at 34 different sites around the UK between 1967 and 2017. Co-author Dr. James Bell from the Rothamsted Insect Survey explained: “Since 1964, the Rothamsted Insect Survey has been at the forefront of the insect declines research, exploiting the longest standardized terrestrial insect time series in the world.
“Even though we have reported on population change in aphids, moths, ladybirds, wasps and general insect biomasses for decades, this study represents a major advance in our understanding.”
Two of the most commonly suggested causes of “Insectageddon’ are agricultural intensification and, for night-flying insects like moths, light pollution. However, the researchers found no evidence that agricultural practices or urban light pollution are the main driving force behind this recent decline.
The researchers categorized the moth trap sites into four land use types: woodland, grassland, arable and urban, and found that land use type (as well as changes over time in land use) had little impact on the pattern of increase and decline.
Dr. Macgregor commented: “If pesticides were causing the problem you would expect to see the biggest decline in arable landscapes; likewise, if it was light pollution, the biggest decline would be in urban environments. We found neither of these to be the case—in fact, the habitats with the biggest decline were woodland and grassland.”
Extreme weather events
Changing weather patterns and climate change could be an explanation, the researchers say. Sharp increases in the amount of moths in the late 1970s came soon after one of the hottest, driest years on record. Disturbance from extreme weather events can sometimes cause equally extreme and unpredictable population changes in insects, including both increases and declines.
Whether climate is contributing to the more recent decline requires further investigation; rising average annual temperatures and rainfall patterns did not match up with the peaks and troughs in moth populations, but extreme weather events—from deluge and flooding to heatwaves and drought—are often not reflected in average climate records.
The post-1982 decline appears to be real, but the researchers concluded that the reasons for this ecological decline are not as straightforward as is sometimes suggested.
“There is no simple explanation and more research on long-term data sets is required” added Professor Thomas. “We found that short-term studies and infrequent sampling can give erroneous estimates of biomass change. The complexity of insect population change requires more, better and longer-running data if we are to draw robust conclusions, particularly for parts of the world where insect data are limited.”
For the next 15 years, Baumann, Moran, and their colleagues used similar DNA analyses to document equally long-term relationships between bacteria and white flies, spittlebugs, cicadas, leafhoppers, and psyllids. Some partnerships dated as far back as 270 million years, they concluded. The work “established that symbiosis is a central part of evolution that goes way back,” Moran says. She and other biologists propose the microbes helped the insects exploit new food sources and habitats, resulting in a rapid diversification that paralleled the diversification of flowering plants.
“Having her as an organismal biologist and him as a microbiologist was really helpful for the field,” McCutcheon says.
The sequencing also suggested why such partnerships have persisted for so long. Buchnera, for example, has genes that enable it to make amino acids not available from sap or from the aphid’s own metabolism, compensating for the insect’s poor diet. Meanwhile, living in the protected environment of the aphid’s specialized bacteria-carrying cells, Buchnera has lost essential genes, so it has to rely on the aphid to make up for those losses. In the late 1990s, this interdependence seemed remarkable, and it helped reshape how symbiosis was viewed.
Moran’s genomic approaches to symbiosis have since inspired many researchers, says Angela Douglas, who studies insect-microbe interactions at Cornell University. Twenty-five years ago, “We were the crazy people” for thinking symbiosis was so important, she recalls. Today, such close connections have proved to be the rule for many host-microbe partnerships.
Moran’s later work in insects confirmed the power of symbiosis. She, McCutcheon, and others found that some insects can’t survive without multiple symbionts. In the glassy-winged sharpshooter and the cicada—both also sap-sucking insects—one symbiont supplies eight of the 10 essential amino acids missing in their diet, and another symbiont supplies the other two. In other sap-sucking insects, symbionts serve additional functions, Moran and her colleagues discovered. In aphids, a symbiont makes the insect less susceptible to parasitic wasps by carrying a virus that’s toxic to the wasp’s young. Other symbionts improve the aphid host’s tolerance for high temperatures, enabling it to thrive in new environments. That work illustrated the complexity of microbial partnerships and hinted at the spectrum of advantages that microbial guests confer, a theme increasingly evident in studies of the human microbiome.
Moran also unexpectedly discovered that deleterious mutations are often common in the hosted microbes, suggesting symbiosis isn’t always a win-win for both partners. The microbial genomes were naturally decaying through time for two reasons: The bacteria lacked a sexual phase of reproduction, which could recombine DNA and replace bad genes, and only a few of the bacteria trapped inside an aphid pass along to the next generation, a winnowing that further restricts recombination between microbes. The buildup of mutations steadily erodes the number of working genes in the bacteria—Buchnera has just 600 genes compared with the 5000 or so powering Escherichia coli—and make those that remain less functional. “The insect is basically relying on a symbiont that’s falling apart,” Moran says.
She and Japanese colleagues later identified one way aphid endosymbionts cope with the decay: by making a lot of heat shock proteins, which can help stabilize faulty proteins produced from the mutated genes. Another bulwark against decay, Moran suggests, is what’s known as horizontal gene transfer, in which essential genes from the partner microbe or outside microbes migrate to the host genome—as genes from mitochondria did. That way they can benefit from the host’s sexual reproduction, which enables intact copies to replace mutated ones.
Moran’s groundbreaking paper on gene decay came out in 1996. Her lab in Arizona was thriving, but her associate professor’s salary barely covered her bills. “I was broke,” she recalls, and nearly overwhelmed being a single mom. Divorced for the second time in early 1997, with a 5-year-old daughter and a 14-year-old stepdaughter, she struggled to balance work and family life. “If you have kids, you are not allowed to fall apart,” she says. Yet she couldn’t travel to scientific meetings—key to any young professor’s career.
The MacArthur grant she received in 1997, which paid more than $50,000 annually for the next 5 years, lifted those burdens. She immediately hired a housekeeper and reduced her teaching load.
At the time, Ochman was studying bacterial genomes. Curious to meet this newcomer to microbial evolution, he prodded organizers of one of the exclusive Gordon Research Conferences to invite Moran. So few women were present that Ochman knew exactly who she was. With characteristic directness, he walked up and asked what she was doing with the MacArthur money. Moran, who tends to be reserved, was charmed. They married 14 months later, and he followed her to the University of Arizona. In 2010, Yale University recruited them to set up a center on microbial diversity. In 2013, the couple moved back to Moran’s home state.
She says their shared passion for evolutionary biology and Ochman’s encyclopedic knowledge of the field have aided her immeasurably. He “has had a huge positive impact on my science.”
Early on, Ochman had been puzzling over two microbial mysteries: why genomes of E. coli strains can vary in size by as much as 50%, and how other bacteria abruptly change from benign to pathogenic. By scrutinizing the microbes’ genomes, he found that they readily gain and lose genes by swapping them with other bacteria or with their hosts. Such horizontal gene transfer could help explain the genome size variation, how bacteria pick up genes for toxins or other weapons—and also how a symbiont such as the ones Moran studies might shift essential genes to its host.
Moran and Ochman have offices less than 100 meters from each other. He often pops in on her, whether to discuss a possible grant proposal, go over the latest data, or just have lunch. “We spend 18 hours a day together,” Ochman says. Yet their personalities are a world apart. Boisterous and impulsive, Ochman jumps quickly into new topics (ape microbiomes recently). Steadfastly loyal, Moran picks a question—or a partnership—and works on it thoroughly. “She is more logical and takes a more long-term view,” Ochman says.
Moran’s continued insect collecting led her to examples of bacterial symbionts with such tiny genomes that they are inextricably tied to host cells. One was Carsonella ruddii, from that psyllid from the Mexican restaurant, which proved to have just 160,000 bases compared with E. coli‘s 5 million bases and Buchnera‘s 640,000. Other genomes were even smaller. The findings have convinced her that no clear dividing line separates organelles and endosymbionts. “My view is that these words are just labels,” she says.
Honey bees have become one of Moran’s enduring interests, prompted by her hypothesis that gut bacteria might play a role in the well-documented decline in the bee population. Her team’s early work showed the honey bee gut contains eight species of bacteria—a manageable number compared with the hundreds typical of the mammalian gut—and that every honey bee around the world has the same set. A student in her lab at Yale figured out how to grow each of the eight kinds in the lab; in contrast, Buchnera continues to be unculturable.
By isolating pupae before they emerge, Moran’s team can keep worker bees from inoculating the young bees with the bacteria. The resulting “microbiome-free” bees, the group found, vividly demonstrate the importance of these microbial guests. Lacking their usual microbiomes, the bees gain less weight, are more susceptible to pathogens, and die sooner. Hives decline.
Recently, Moran’s graduate student Erick Motta showed that bees with an intact microbiome become more susceptible to pathogens when exposed to glyphosate, the herbicide marketed as Roundup. Glyphosate has been considered harmless to insects and other animals because it affects an enzyme that only plants and microbes use. But through its effects on microbial guests, the compound may harm insects as well, the work suggested. (When this work was published last year, Roundup’s maker issued a statement saying: “No large-scale study has ever found a link between glyphosate and honey bee health issues.”)
To Moran, the honey bee microbiome is complex enough to stand in for the human microbiome but simple enough to be dissected in a way the human counterpart cannot be. Moran’s work on bees “has been some of the most reliable, clearly articulated work” on gut microbes, says Jon Sanders of UC San Diego, who studies human microbiomes. He expects the honey bee studies will yield insights into how gut microbial communities in general function.
The bee work led to other payoffs after Moran started to work with the Defense Advanced Research Projects Agency (DARPA). which sought proposals to harness microbial systems. At first she hesitated: “The purpose was to engineer something, rather than simply to understand something, as had been true for all my work up until then,” she explains. But she, UT bioengineer Jeffrey Barrick, and Ellington got DARPA funding to devise methods to alter the bee microbiome in ways that would change the insect’s traits. Such tinkering might make bees more resistant to stresses, for example, which could help preserve the vital pollinators. To show a proof of principle, UT graduate student Sean Leonard recently engineered a bacterium from the bee gut to produce RNA that increases production of dopamine, a key neurotransmitter. Preliminary results suggest those bees are better learners as a result.
Colleagues are curious to see what Moran learns next from honey bees or any of the insects whose inner lives she probes. “She’s not just a one-hit wonder,” says Ute Hentschel, a marine biologist at GEOMAR-Helmholtz Centre for Ocean Research Kiel in Germany who studies sponge-microbe symbioses. “She has an amazing capacity to focus things so that [new insights] precipitate out.”
Moran believes that, like most complex partnerships, the unions between insects and microbes will take a lifetime to unravel. “The host and the symbiont communicate in ways we don’t understand,” she says. “We’re working to figure that out.”
A mysterious disease is starting to kill American beeches, one of eastern North America’s most important trees, and has spread rapidly from the Great Lakes to New England. But scientists disagree about what is causing the ailment, dubbed beech leaf disease. Some have recently blamed a tiny leaf-eating worm introduced from Asia, but others are skeptical that’s the whole story.
Regardless of their views, researchers say the outbreak deserves attention. “We’re dealing with something really unusual,” says Lynn Carta, a plant disease specialist with the U.S. Department of Agriculture (USDA) in Beltsville, Maryland.
American beech (Fagus grandifolia), whose smooth gray trunks can resemble giant elephant legs, can grow to almost 40 meters tall. It is the fifth most common tree species in southern New England and in New York state—and the single most common tree in Washington, D.C. Its annual nut crop provides food for birds, squirrels, and deer.
Beeches in the United States were already struggling with a bark-infesting fungus when, in 2012, biologist John Pogacnik of Lake Metroparks, which manages natural areas in Ohio’s Lake County, spotted trees with leaves that were shriveled and had black stripes. By 2018, foresters had documented beeches with similar symptoms in 24 counties in eastern Ohio, western Pennsylvania and New York, and Canada’s Ontario province. Small trees with shriveled leaves were starting to die; on larger beeches, the symptoms crept up the tree toward leaves in the canopy. Worried foresters began to pry loose research funding from USDA and other agencies, and organized a meeting to discuss the disease in May 2018 in Parma, Ohio.
There, plant pathologist David McCann, of the Ohio Department of Agriculture in Reynoldsburg, said he had found thousands of wriggling worms streaming from infected beech leaves. He sent Carta samples of the worms, which can be up to 2 millimeters long. Carta identified the worm as a subspecies of Litylenchus crenatae, a nematode that is found in beech trees in Asia but doesn’t kill them. The find was eye-opening, Carta says, because no leaf-eating nematode is known to infect a large forest tree in North America.
Next, Carta, together with biologist David Burke of the Holden Arboretum in Kirtland, Ohio, and others, sought to verify Koch’s postulates—pathology’s gold standard for verifying a putative cause of a disease. The researchers took nematodes from diseased trees, pipetted them onto the buds of young, healthy trees in a greenhouse, then waited for symptoms to appear and reisolated the nematode from the affected leaves. The results of the experiment, which Carta presented at a conference in July and which have been accepted for publication in the journal Forest Pathology, indicate that “nematodes are causing beech leaf disease,” Burke says. “We feel like we’ve closed Koch’s postulates.”
Enrico Bonello, a plant pathologist at Ohio State University in Columbus, is skeptical. He and a graduate student, Carrie Ewing, have ground up leaves from diseased and healthy looking beeches and then extracted fragments of DNA and RNA. They found nematode DNA in both healthy seeming and diseased trees. In diseased beeches, they also found evidence of three bacteria and three fungi not found in healthy looking trees. They don’t know whether any of the microbes sicken trees. But Bonello says the finding, which he plans to present at an upcoming conference, “raises questions” about the role of nematodes. Perhaps, he says, the worms are simply transmitting a microbial pathogen that is the disease’s true cause.
Carta’s team, however, considers that scenario “highly unlikely.” She contends nematode feeding alone could sicken trees.
Whatever its cause, beech leaf disease is getting around. Connecticut officials last month announced detections in Greenwich, Stamford, and New Canaan, on New York City’s doorstep. Diseased trees have also been found on Long Island in New York state, some 800 kilometers from the malady’s ground zero. Carta and others are investigating whether the nematode is being moved across the landscape by mites found on infected beech trees, or by birds.
USDA’s Animal and Plant Health Inspection Service, the agency responsible for dealing with invasive tree killers, is helping study the disease. But it has held off on taking action to limit the disease until it knows more about the cause and how it spreads.
The beech’s plight has dismayed forest experts, who are already reeling from an onslaught of introduced tree killers such as the emerald ash borer beetle that has eliminated millions of trees. “I think we should be alarmed,” says Robert Marra, a forest pathologist with the Connecticut Agricultural Experiment Station in New Haven. “What’s going to be left in forests?”
The beech may face additional threats. Earlier this year, U.S. Forest Service researchers announced they had found an undescribed beetle on stressed European beech trees in a New York City cemetery. The scientists are now studying whether the insect also has a taste for American beech.