Nebraska: Biocontrol of the wheat stem sawfly

Jeff Bradshaw

PREVALENT PEST: A Nebraska survey found all dominant grass species had some level of infestation of stem sawfly, along with some level of sawfly parasitism.

Parasitoid wasp still the most effective control for wheat stem sawfly in Nebraska.

Jan 15, 2019

By Jeff Bradshaw and Bethany Bergstrom

Nebraska Extension has conducted a wheat stem sawfly survey for several years. The sawfly survey was discontinued in 2017; however, data from the survey are being used strategically for grassland and on-farm evaluation of sawfly-parasitoid relationships.

Extension is conducting a survey and landscape analysis to better understand the ecology of both the wheat stem sawfly and its parasitoid in Nebraska. The parasitoid wasp that attacks sawfly larvae in wheat stems is currently the most effective control method for the wheat stem sawfly in Nebraska.

Because the wheat stem sawfly is native to North America, it infests many grasses (not just wheat). Because parasitoid-sawfly relationships may have had more time to co-evolve in a native setting (e.g., the Nebraska Sandhills), the survey is conducting transects that span both wheatland and grassland regions. In both regions, Extension is surveying grassland species from borrow pits to rangeland to seek out both sawflies and sawfly parasitoids.

Extension is collecting sweep net samples and stem samples through the survey range to better understand the role of grasslands in sustaining or regulating sawfly populations. However, the focus is on identifying plants and habitats that may encourage greater conservation of sawfly parasitoids and biological control mechanisms.

Results so far have found:

  • Some of the most dominant grassland plants in the survey are crested wheatgrass, intermediate wheatgrass, needle and thread, sand dropseed, and smooth brome.
  • All dominant grass species had some level of infestation of stem sawfly (Table 1). Smooth brome had the highest infestation level (average of 43.4%).
  • All dominant grass species had some level of sawfly parasitism. The highest proportion of sawfly parasitism was found in intermediate wheatgrass (about 19%).
  • Further analysis is underway to relate findings in grasslands to wheatland.
Table 1. Dominant grass species sampled from grassland habitats for wheat stem sawfly and sawfly parasitoids in 2018 (n = 32
Source: UNL CropWatch

Bradshaw is an Extension entomologist, and Bergstrom is a University of Nebraska-Lincoln entomology graduate student. This report comes from UNL CropWatch, which is solely responsible for the information provided and is wholly owned by the source. Informa Business Media and all its subsidiaries are not responsible for any of the content contained in this information asset.

Kenya: Resistance to TuMV disease in cabbage and kale

A team of international scientists from CABI, the Kenyan Agricultural and Livestock Research Organisation (KALRO), NIAB EMR (UK), University of Warwick (UK) and Syngenta (Netherlands) are seeking to improve the resistance of Kenya’s cabbage and kale crops to Turnip mosaic virus (TuMV).

In the distantly-related Chinese cabbage (Brassica rapa), a potentially durable TuMV disease resistance trait was identified by Professor John Walsh at the University of Warwick, while work by Dr Charlotte Nellist, of NIAB EMR, UK, Dr Bill Briggs, of Syngenta, and Prof Walsh elucidated the novel mechanism of TuMV resistance.

The scientists are now working to employ conventional breeding methods to move the resistance trait from Chinese cabbage to Kenyan cabbage and kale varieties in the anticipation that providing durable disease resistance in Kenyan cabbage and kale cultivars will help reduce yield losses.


The lower cost of production, the researchers believe, will hopefully result in cheaper retail prices – making the crops more available for consumption and helping in the fight against malnutrition.

In addition, the project aims to survey the prevalence of TuMV from multiple regions in Kenya and provide data on the efficacy of the Chinese cabbage resistance against contemporary Kenyan TuMV isolates.

Miriam Otipa, Head of Pathology at KALRO, said, “KALRO is excited to be part of this team that is solving a challenge for an important Kenyan vegetable that has not been tackled by any one so far in Kenya. The training of scientists in the use of modern molecular tools to breed for resistance is an area that is challenging for the organisation. The collaboration will foster the exchange of ideas among scientists from the UK and Kenya, thus enriching their knowledge.”

Turnip mosaic virus on kale

Turnip mosaic virus aphid vectors (Brevicoryne brassicae, ‘cabbage aphid’) present in substantial numbers in a kale crop, Subukia, Nakuru, Kenya.  Photo credit: C. Nellist.

The project kicked off with a field sampling trip in March 2019, visiting four cabbage and kale growing regions of Kenya; Kinangop, Kinale, Subukia and Molo. The virus was detected in all four regions visited to varying degrees, with higher incidence in Subukia and Molo.

In addition, aphid vectors were observed at every individual farm visited across the four regions.  TuMV isolates have been collected and are currently being screened on the Chinese cabbage resistant material to ensure the resistance is functional against Kenyan isolates of TuMV.

A crossing programme has been designed to transfer the resistance from the Chinese cabbage to cabbage and kale and will employ embryo rescue techniques to deal with incompatibility issues faced when crossing two different species.

Dr Joseph Mulema, Senior Scientist based at CABI in Kenya, said, “This project is line with CABI’s international development agenda and outputs from this work will be used in developing fit-for purpose information materials for use by smallholder farmers growing brassicas in Kenya.

“In addition, there will be a wider reach for these materials because they will also be added to the Plantwise Knowledge Bank, the online resource of the Plantwise Programme.”

Additional information

The project was funded through the Community Network for African Vector-Borne Plant Viruses (CONNECTED), which is financed by the UK Government’s Biotechnology and Biological Sciences Research Council (BBSRC), through the Global Challenges Research Fund (GCRF).

For more information visit the project page.

Project partners

Dr. Charlotte F. Nellist (NIAB EMR, UK)

Ms Miriam Otipa (KALRO, Kenya)

Prof John A. Walsh (University of Warwick, UK)

Dr Joseph Mulema (CABI, Kenya)

Dr Bill H. Briggs (Syngenta, the Netherlands)

Relevant papers

Spence, N. J., Phiri, N. A., Hughes, S. L., Mwaniki, A., Simons, S., Oduor, G., Chacha, D., Kuria, A., Ndirangu, S. and Marris, G. C. (2007) Economic impact of Turnip mosaic virus, Cauliflower mosaic virus and Beet mosaic virus in three Kenyan vegetables. Plant Pathology 56, 317-323. DOI: 10.1111/j.1365-3059.2006.01498.x

Nellist, C. F., Qian, W., Jenner, C. E., Moore, J. D., Zhang, S., Wang, X., Briggs, W. H., Barker, G. C., Sun, R. and Walsh, J. A. (2014) Multiple copies of eukaryotic translation initiation factors in Brassica rapa facilitate redundancy, enabling diversification through variation in splicing and broad-spectrum virus resistance. The Plant Journal 77, 261-268. DOI: 10.1111/tpj.12389

Huanglongbing-sniffing dogs | Global Plant Protection News

In an abundance of caution, some commercial citrus growers in Ventura County, Calif. elected to remove numerous trees after dogs from Florida trained to detect the presence of the bacterium responsible for Huanglongbing (HLB) alerted on over 200 trees.

The dogs are owned by a private company and are trained to sniff for signs of Candidatus Liberibacter asiaticus (CLas), a bacterium believed by researchers to be the cause of the citrus disease responsible for greatly reducing Florida’s citrus production and for infecting residential trees in southern California.

To date HLB has not been confirmed in commercial citrus groves in California. The disease is present in residential citrus throughout southern California, prompting the state to remove trees that test positive for the bacterium to control its spread.

John Krist, chief executive officer of the Ventura County Farm Bureau, said growers in his county remain concerned with the proximity of the disease to their groves and the length of time it takes for trees to be formally diagnosed with the disease through a scientific process known by the industry simply as “PCR.”

The Polymerase Chain Reaction (PCR) test is a scientific method used to amplify DNA and remains the only regulatory-approved means to declare whether a citrus tree has the disease. It can take years for a tree infected with the bacterium to elicit symptoms or contain enough bacteria to test positive.

Dogs as early detection

The trained dogs are considered by some as a viable early detection tool to aid growers in determining whether their trees are infected. Nevertheless, the dogs are not a government-approved option to declare presence of the bacteria. For growers, this means that even a positive “alert” by dog teams will not otherwise open them to quarantine restrictions.

Earlier this year the Ventura County Farm Bureau contracted with F1K9 in Florida to scout commercial groves in the county for HLB, according to Krist. Similar teams of dogs were previously used in California to scout citrus trees in the University of California’s research grove at Riverside, and at the UC Research and Extension Center at Lindcove in Tulare County. In those instances, several trees at UCR were alerted on by dogs while none of the trees at Lindcove were alerted on by the dogs.

To date UCR has not removed those trees from its research grove. Instead, the trees are covered with netting to prevent access by the Asian citrus psyllid (ACP), the tiny insect believed to be solely responsible for the spread of HLB. Those trees are said to be the subject of ongoing testing and research.

In late July and early August, four dogs, along with their handlers, scouted commercial groves in Ventura County, inspecting about 3,500 trees on 20 properties, according to Krist. Out of that the dogs alerted on 211 trees. Those trees have since been removed and destroyed by their owners.

The genesis of the Ventura dog inspection came from an understanding of research led by Dr. Timothy Gottwald, a plant pathologist with the U.S. Department of Agriculture.

The Gottwald research points to the ability of trained dogs to detect the CLas bacterium. These dogs, which a Gottwald article says have been evaluated in laboratory and field experiments, can detect CLas over 95 percent of the time in commercial groves, and over 92 percent of the time in residential citrus. Perhaps more importantly, these dogs can do this well before a PCR test could result in a positive diagnosis.

That is essentially why the Ventura County Farm Bureau, at the request of local citrus growers, requested the dogs. Krist says they cannot afford to wait for the state to find and declare HLB in commercial citrus through regulatory testing.

Krist is concerned that ongoing state efforts to find HLB appear targeted at residential citrus, with little focus on commercial groves.

“They need to start doing a more systematic survey of commercial citrus than they’ve been doing up to now,” Krist says of CDFA efforts.


News of the dogs’ findings rippled through the commercial citrus industry in California.

Victoria Hornbaker, director of the California Citrus Pest and Disease Prevention Division, a new division within the California Department of Food and Agriculture, says there are no confirmed cases of HLB in Ventura County. Moreover, she said the state was not involved in the dog inspection there.

Krist says the goal never was to have the trees PCR tested because growers believe the tests would be negative due to the inability of the PCR test to definitively detect CLas infection in all cases.

California Citrus Mutual President Casey Creamer said that while dogs can be an effective tool, he and others in the industry became concerned by a published news article that implied HLB was found in the commercial groves when that determination cannot be made solely by a dog.

“Our biggest concern was the messaging,” Creamer said, adding that the jury is still out on the effectiveness of the dogs under California conditions.

Citrus Mutual and others in the industry are said to be working on a public response to what many in the industry agree is the inevitable discovery of HLB in commercial citrus in California.

Hornbaker said that testing of plant materials and insects collected in Ventura County in 2015 and 2016 showed “inconclusive” results, meaning some samples taken revealed levels of bacteria too few to declare a positive result under regulatory rules, but enough bacteria that inspectors could not declare a “negative” result. Since then the USDA changed its testing protocols after researchers determined early tests may have “cross-amplified” multiple forms of bacteria in the samples that could have led to a “false positive.” Testing protocols were ultimately tightened to specifically seek only the CLas bacterium regulators are looking for.

What do we know?

Some scientists now believe that the latency of this disease – the period between first infection by ACP feeding activity and when a PCR test will reveal a positive result – may be much longer than the 2-3 years first thought. It’s this latency that concerns growers and led to the use of dogs as an early detection method. Published information by Gottwald suggests these dogs can detect parts-per-trillion levels of the bacteria, which is more sensitive than most laboratory instruments and certainly more sensitive than the PCR test.

A Gottwald article also states that canines studied under Florida conditions, when using potted citrus trees, were able to detect CLas in some trees as early as two weeks after infected psyllids fed on them.

Dr. Beth Grafton-Cardwell, a University of California entomologist and a collaborator in some of the Gottwald studies, is surveying for the presence of ACP in commercial citrus groves in southern California, to include the Ventura County region. She says those surveys have turned up very few psyllids this year, which she attributes to the weather and amplified efforts by growers to treat their groves in unison with approved insecticides as a best management practice. It is believed that a coordinated treatment of groves in a region is the best method to control psyllid populations.

Grafton-Cardwell is one of those scientists who believes that HLB latency may be longer in some cases as the disease may never go systemic in the entire tree, hence the inability for the PCR test to catch it in all cases.

“Everybody here in Ventura County is staring this epidemic in the face and felt a real need to be proactive,” Krist said of the recent dog visit. “Once the disease takes hold, you’re never going to get in front of it. That was the mistake Florida made.”

Krist says there are plans to bring the dogs back in November and again in January to do more scouting of commercial citrus groves.

Neonicotinoid pesticides and anorexic birds

White-crowned sparrows stop eating after they ingest small amounts of neonicotinoid pesticides.

Margaret Eng

When birds migrate, timing is everything. Fly too late, and they miss the peak season for finding good food, a good mate, or a good nest site. But that’s just what may happen to migrants unlucky enough to eat pesticide-laced seeds, new research shows. Toxicologists studying white-crowned sparrows have shown that these large, grayish sparrows become anorexic after eating neonicotinoid pesticides, causing them to lose weight and delay their southward journeys. The study might apply to other birds as well—and help explain the dramatic songbird decline of recent decades, researchers say.

Neonicotinoids are the world’s most widely used class of pesticide. They protect seeds—and the plants that grow from them—from insects resistant to other pesticides. But scientists have recently found that they can decimate pollinators like honey bees and bumble bees. Such concerns led the European Union to ban three of these compounds in 2018.

Laboratory studies have shown that neonicotinoids sicken and disorient captive birds, but no data existed on how they affect wild birds, who often swoop into fields to nosh on pesticide-laced seeds. Wondering whether pesticide exposure might explain a massive recent decline in farmland bird species, Margaret Eng, an ecotoxicologist at the University of Saskatchewan in Saskatoon, Canada, and her colleagues got to work.

The researchers caught dozens of white-crowned sparrows (Zonotrichia leucophrys) in southern Ontario province in Canada as the birds migrated from the Arctic to the southern United States. They kept the birds in cages with food and water for 6 hours. About a dozen received low doses of the neonicotinoid imidacloprid—equivalent to what they might ingest had they eaten several seeds from a recently planted field. Another dozen got a lower dose of the pesticide, and control birds received the same handling but no pesticide. After 6 hours, Eng put a tiny radio transmitter on each bird’s back and released it into a 100,000-square-kilometer site in Ontario, where 93 regularly spaced radio towers track tagged animals.

Within hours, birds with the highest pesticide dose lost an average of 6% of their body weight and about 17% of their fat stores, which are key to fueling long flights, Eng and colleagues report today in Science. Over the course of those 6 hours, the birds given pesticides stopped eating, taking in about one-third the food that untreated birds ate, they note.

Nor did the birds recover quickly when released. Half of the high-dose birds stuck around Ontario an extra 3.5 days or longer. “It’s just a few days, but we know that just a few days can have significant consequences for survival and reproduction,” Eng explains. She thinks the birds needed that extra time to get the pesticide out of their systems, start to eat again, and regain their lost fat.

The paper provides “a compelling set of observations” that shows how even low doses of neonicotinoids can affect bird survival and reproduction, says Mark Jankowski, a toxicologist at the University of Minnesota in St. Paul who was not involved with the work. These effects could help explain declines in sparrow populations—and may apply to other birds, says Caspar Hallmann, an ecologist at Radboud University in Nijmegen, the Netherlands. But more work would be needed to prove that, Jankowski adds.

Few researchers think the United States or Canada will have the political will to ban neonicotinoids despite the harms, because they are so protective for plants. But there are workarounds, says Nicole Michel, a population biologist with the National Audubon Society’s Conservation Science Division in Portland, Oregon. For example, rather than treat all seeds before they are planted, farmers could save money and reduce birds’ exposure by applying the pesticide to plants only after an insect outbreak occurs. Jankowski says researchers could also explore other methods to reduce birds’ exposure, including coming up with better ways to bury seeds—and remove those that spill—during planting.

What herbaria tell us about crop pathogens

Ever since we domesticated the first plants for food production, humanity has been dragged into the age-old arm’s race that exists between our crops and their pathogens…

The impact of one single crop pathogen on human society can be of a dreadful scale, especially when our crops are not naturally protected against them. The best example to illustrate this is the potato epidemic that caused the Great Irish famine in the mid-19th century. The culprit, an American microbe named Phytophthora infestans, crossed the Atlantic by ship, reached the European continent and wiped out entire potato harvests over various consecutive years. The impact was most devastating in Ireland, where people were highly dependent on one single variety of potato that did not bear strong natural resistance against the pathogen. About a million people died of starvation and another million or more were forced to leave the country. The famine reduced Ireland’s population by 25%, and the country has still not yet recovered to its original population size, even today.

It would, nonetheless, be very wrong to think that the threat of starvation due to crop pathogens is a problem of the past. According to the Food and Agriculture Organization (FAO) of the UN, at least 20% of global food production is lost due to plant disease and over 800 million people are chronically undernourished worldwide. In addition, the globalisation of trade since the Second World War combined with a lack of thorough disease control has allowed the spread of local pathogens to every corner of the world. And now, with the threat of climate change coming nearer and nearer, the future of agriculture in the face of disease becomes more uncertain. Simply eradicating pathogens is, however, practically impossible and ecologically irresponsible. What would provide us with more sustainable ways of combating crop disease and hunger, and equip us better for the changes to come, is a thorough understanding on how plant pathogens spread, colonise and adapt to their hosts in the first place, so that our agricultural systems can always be a step ahead of disease. For that, the history of a crop pathogen and its spread is a great starting point.

Studying the evolutionary history of plant pathogens, and tracking their routes of invasion, has always been difficult, however, because the historical crop disease records are sparse in this respect. Moreover, these records often provide misleading information on the spread of the disease as it can take a long time before the presence of a pathogen becomes apparent. This means that its true arrival time and subsequent adaptation to its new environment might have happened years before historical documents suggest. In recent years though, genetic sequencing technologies have taken a giant leap forward such that it has now become possible to sequence entire genomes of all kinds of organisms – even dead ones –  rapidly, cheaply and accurately. Scientists have developed intricate methods to obtain the remaining DNA from tissues that have been dead for thousands of years and have made astonishing discoveries. For example; through the few micrograms of DNA obtained from a Neanderthal bone, it was discovered that we, Homo sapiens, actually intermixed with this other species of hominid. For decades, such an idea had been thought impossible. And while most ancient DNA studies focused on humans and other animals, more recently scientists have begun to find other applications for this promising field of genetics.

To witness significant evolutionary change in humans – organisms with a long generation span – you need to go deep back in time and study them over a couple of centuries or millennia at the least. Microbes on the other hand, are organisms with much shorter generation spans. In their evolutionary context, time is warped: 100 years of change could be equal to millennia of evolution for us. With this idea in mind, scientists started to retrieve microbial pathogen DNA from the dead, dried leaves of old herbaria tucked away in the dark and dusty libraries of botanical gardens worldwide. Indeed, thanks to botanists from the 17th, 18th and 19th century, we have a magnificent plant collection covering all existing and also many extinct species of plants in all forms: old and young, tall and small, healthy and sick. Sequencing the DNA of historical microbes in herbarium samples revealed information on plant pathogens we couldn’t have obtained in any other way. Pioneer studies mostly concentrated on Phytophthora infestans and tracked down the original strain and the invasion route that brought it to Europe, planting death and despair wherever it went.

Through the University of Montpellier, I had the chance to explore this exciting field of ancient genetics, herbarium specimens and pathogen histories myself. For that, my destination was a very special place: the tiny French island of La Réunion, which lies in the middle of the Indian Ocean. There, a couple of scientists at the Research Institute for Agriculture and Development had started to study infected herbarium samples of citrus plants to find out more about the bacterial pathogen Xanthomonas citri (hereafter Xac). Although absent in Europe thanks to the strict border control and quarantine policies of the EU, this microbe is a nuisance in the rest of the world, causing lesions on the fruits and leaves of citrus plants, and premature drop, which makes the fruits inedible and unsellable. When I arrived on la Réunion, very little was known about this pathogen: its origin was thought to be Asia and it was believed to have spread to the rest of the world in the past century and a half. But how and when it reached those places, including La Réunion itself, was unknown; nor was it clear whether the spread had been facilitated by human trade and transport. And scientists also had no idea how fast it could adapt and evolve. These things are nevertheless documented in its inner “genomic” book, which reveals more than any historical document in the world.

Obtaining the DNA sequence of decades-old dead microbes is not an easy task. I spent the first two and a half months of the project in the lab, desperately trying to avoid contamination from modern Xac samples and testing multiple methods to obtain as much DNA as possible from the dead tissue. After getting the sequences back, we spent a further month trying to clean and organise the heavily-damaged data. In the meantime, I was also enjoying to the full the natural wonder that is La Réunion.

Being a young island, moulded and shaped by the violence of a fierce volcano, it is a strange little paradise for those who love to wander and hike. The landscape is scarred by the violent natural forces that created it, with slopes climbing up steeply from the coast to reach dizzying 3000m heights and then plummeting into a clover-like calderas that arose when the volcano came to its own brutal end, crashing down half a million years ago. Although the coast has been intensely urbanised, the inner parts of the island still remain wild. The hectic landscape, with razor-sharp cliffs, deep ravines, abrupt peaks and the impressive, straight walls of the calderas has created a lot of opportunity for a fantastic variety of natural communities to settle: grasslands, forests, jungles, rivers and waterfalls – while making it very hard for humans to reach. In the south-eastern end of the island a younger, very lively little brother of the now-extinct volcano sprung up about 500,000 years ago and is now one of the most active volcanoes in the world. Also here, landscapes vary immensely, with cool, green grasslands rolling into vast, red sand plains as you climb higher and higher into the mouth of the dragon. It is surreal to think that one can find himself in the prairies of the Alps, the plains of Tatooine, the forests of Middle-Earth and the jungles of Jurassic Park on the very same piece of land that only just stretches 63 km long.

The caldera of Cilaos lies in the centre of la Réunion and is the result of the main volcano’s collapse half a million years ago.

Looking back, it is hard to decide which of all the fantastic things I saw in La Réunion struck me most. Was it that humpback whale jumping metres high into the air, or the view of two encircled worlds as I stood on the ridge that separated one caldera from the other? Was it the splendid primary jungle that lies tucked between the calderas, bursting with life, covered in fog; or the view of the milky way from a white-sand beach; or the eerie look of a gigantic blood moon crossing the skies? If I had to pick, I believe it would be the view of streams of lava pouring out of the wounded earth one night in April, when the island’s volcano erupted. The trembling and growling underneath our feet, the sight of deep-cutting, red-glowing crevices from which fiery lava was spitting, and the slowly-growing, red tongues of liquid stone rolling towards the sea made me realise what a strange, powerful force is hidden deep in the Earth, one that can so easily destroy life, and give birth to it at the same time. Even though it was the very same Earth that was being vomited onto the surface before my very own eyes, it was by far the most unearthly and surreal thing I’ve seen and felt in my life.


The 500 thousand year old volcano in the South-East of La Réunion is one of the most active in the world. Here we see its main crater, le Dolomieu, in the back, and the much smaller and younger crater Formica Leo in front, which is thought to have been formed in the mid-18th century. 

While I was able to witness these spectacular natural scenes on the weekend, I was gradually being absorbed with the wondrous feeling of obtaining scientific results and acquiring a better understanding of our study system, Xac during the week. Once our historical DNA sequences were ready for analysis, we paired them up with DNA sequences of contemporary Xac strains from the entire world. This revealed the genetic relationship between historical and modern strains and lifted a tip of the curtain that covers its history. Our analyses confirmed what historical documents had suggested; that Xanthomonas citri is indeed native to Asia. However, something that historical documents cannot accurately report is the arrival date of a pathogen to a new territory. With a large enough sample size, and the availability of historical genomes, we were able to estimate this for the strains that have colonised the islands of the southern Indian ocean: Comoros, Mayotte, Mauritius and la Réunion itself. Our analyses suggested that the bacterium arrived first in Mauritius and la Réunion around 1850. Curiously, this falls shortly after the abolishment of slavery, which caused a major loss of work force on the sugar cane fields that largely fuel the economy of both islands. To replace the now-freed slaves, the French and British colonists brought large groups of workers from other colonies to the islands: many of them coming from India and China. Although we have no direct proof, one could speculate that it was this big migration wave that brought the first Xanthomonas citri to the Indian Ocean, as the migrants carried plants and seeds with them.


The primary forest of Bélouve lies on a plateau in between two calderas. The combination of past volcanic activity, a high altitude and humidity brought by fog that builds up here has given rise to this fantastically biodiverse tropical jungle. 

Another surprising finding was the close genetic relationship between Xac strains of La Réunion and another French island, Martinique. Martinique, however, is located in the middle of the Caribbean Sea, half a world away from La Réunion. How then, can it be that the two strains are so closely related? One possibility is that Xac was transported to Martinique through human traffic and trade, which has created a quick connection between the two French islands. Our results thus suggest that human mobility has possibly played a large role in the spread of the pathogen and reconfirms the importance of thorough border controls and quarantine policies for crops.

How else can these fundamental studies benefit society, you might ask? Apart from creating a historical record on crop disease, such phylogenetic studies can have direct applications. We were, for example, not only able to date the arrival of Xanthomonas citri to the Southern Indian Ocean, but also to estimate a mean mutation rate for its genome. This is a measure for the pace at which mutations occur in the Xac genome, and therefore also for the speed at which it is able to evolve. Such measures are incredibly useful when designing strategies to combat the disease: it gives us an idea how quickly it could adapt and overcome a pesticide, for example. Thanks to such knowledge, we can make sure we’re always a step ahead of the pathogen in the eternal arms race we have found ourselves locked in since our hunter-gatherer ancestors started growing the first crops.

landscape, mountain

Sunrise view over the highest mountain of la Réunion, the Snowpeak, and the surrounding calderas. In front, smaller, extinct craters from times long-gone spring up across the landscape. The picture was taken from the grassy, rural plains that lie at the foot of the volcano. Here, cows graze and oaks grow, as if it were a little piece of Europe brought to this remote island. 

Five months after my arrival in La Réunion, I was on my way again to the airport, with the scientific report of my project and a fantastic collection of unforgettable memories as extra luggage. More than anything, I felt extremely lucky that I had been given the chance to travel there and explore the island’s beauty and magical phenomena, while also learning so much on the evolution of crop pathogens and the unimaginable potential that lies hidden in the millions of herbarium samples across the world. Now that we have the tools to genetically study them, an entire new world of adaptation and evolution has opened up to us, that will certainly provide answers and applications when we face agricultural crisis due to pathogens, climate change or anything else. Most to thank are all those botanists from centuries past which, although oblivious of the true value of their work, knew how to treasure the accumulation of basic, fundamental knowledge about the world that surrounds us. That was one of the key lessons learned while staying in la Réunion; collecting information and knowledge about the natural world just for the sake of curiosity is never in vain, for one can never know what applications we may find for it in the future. And in that aspect, the potential of herbarium libraries is unmeasurable. If only a few historical strains were able to elucidate key aspects of Xanthomonas citri’s evolution and spread, can you imagine what we can learn from the immense natural library that all those botanists from centuries ago left us?

India: Fall armyworm ravaging fields of corn, sorghum, bajra, ragi and sugarcane.

By Manupriya 

  • After ravaging cornfields of sub-Saharan Africa, the fall armyworm arrived in India in 2018. The pest infestation has already spread to most parts of the subcontinent and has been reported from maize farms in 20 states.
  • A native of America, the fall armyworm has spread through trade routes to Africa and Asia. There is no single solution to get rid of this voracious eater of maize plants, and scientists suggest a multi-pronged approach depending on geographical location and extent of the infestation.
  • Maize monoculture and overuse of pesticides that increase resistance have turned the fall armyworm into a serious pest. A shift towards agro-ecological approaches like organic and natural farming, and multiple cropping systems could help in managing the outbreak.

Maize farmers in many parts of Karnataka were taken by surprise in July last year when an unknown caterpillar attacked their crop. It didn’t take scientists long to identify the new pest. By the second week of July, researchers from the National Bureau of Agricultural Insect Resources (NBAIR), an institute under the Indian Council for Agricultural Research, said the new pest was the Fall Armyworm (FAW).

Spotted in a maize field in Chikkaballapur, some 60 km from state capital Bangalore, the appearance of FAW in India is a cause for serious concern. Native to tropical and subtropical regions of the Americas, the dreaded caterpillar appeared and spread rapidly in Africa in 2016, and has since then devastated millions of hectares of maize crop in all parts of sub-Saharan Africa.

And sure enough, the worm spread very fast through the maize fields of India as well. In a matter of months, more than 14 states in the country reported the infestation last year, seriously compromising the corn harvest. The infestation has since spread even wider this year to 20 states, with the northeastern parts of the country the worst affected.

The caterpillar stage of a moth, the FAW (Spodoptera frugiperda) is a voracious eater of maize plants and has been termed as an invasive species by scientists. It’s not a picky eater though. Besides corn, it likes to feed on the leaves and stems of more than 350 plant species, including rice, sorghum, sugarcane and wheat.

An adult female moth can lay up to a thousand eggs in her lifetime. They are also terrific fliers and can travel up to 100 km in a single night.

Fast spread

The spread of FAW through the Indian subcontinent has been particularly fast. In 2019, the pest has spread as far as Mizoram in the northeast, Uttar Pradesh in the north, Gujarat in the west, Chhattisgarh in central India, and several states in the south. This year, the biggest victims so far have been farmers in the northeastern states, where a cumulative of 10,772 hectares of maize crop has been affected. The pestilence has been reported from 20 states in India.

Scientists are not surprised at the fast transmission of FAW. “We have already seen in Africa that the infestation spread from one country, Nigeria, to almost half of the continent in a matter of two years (2016-2018),” said Malvika Chaudhry, regional coordinator, Plantwise Asia, Centre for Agriculture and Bioscience International (CABI).

The northeastern states with their “high humidity and moderately high temperatures” are suitable for the spread of FAW. Its metabolic rate is well supported in these conditions, sometimes even leading to “intensification of infestation,” said Chaudhry. It means that the pest is able to complete its lifecycle in a shorter period of time, resulting in more pests, more quickly.

Farmers and scientists are now fighting to contain the infestation. Maize is India’s third most important cereal crop after rice and wheat. In 2016, 25.9 million metric tons of maize  was produced in India. In 2017, that number rose to 28.7 million tons. In 2018, however, production fell by 3.2% to 27.8 million tons. It is expected that the net production will decline further in 2019 due to the pest attack.

Cascading effect

Although corn is not a staple in India, it serves an important role as feed for poultry. The growth in the poultry industry has resulted in a concomitant increase in the area cultivated under maize since the turn of the millennium. The decrease in maize production thus has a cascading effect on the poultry industry.

Earlier in August, poultry farmers in Karnataka and Maharashtra urged Narendra Singh Tomar, India’s farm minister, to urgently import maize to meet a shortfall. Due to the deficit, maize prices have shot up, resulting in an increase in production cost for chicken and eggs.

It’s not just the feed and starch industries that are feeling the heat. Maize farmers maize are too facing additional challenges in continuing to grow the crop. They’ve had to endure crop losses and bear the additional cost of rescuing their crop from FAW and preventing further infestation.

“The input cost of growing maize has gone up,” said Bhagirath Choudhary, founder-director of South Asia Biotechnology Centre (SABC), a New Delhi-based scientific organization. In addition to the usual input cost, farmers have to spend on pheromone traps, safety kits, botanical and biological control methods and more pesticides.

In addition to their price, most of these items attract high taxes to the tune of 18 percent. Only botanical and biological controls are taxed at five to 12 percent. For farmers, especially smallholders, these costs are punitive. “The SABC has submitted a request to the Union Minister of Finance, Nirmala Sitharaman, to either completely exempt GST (Goods and Services Tax), or reduce it to the lowest slab on these items,” said Choudhary.

Worryingly, FAW seems to have spread to crops other than maize as well. For example, scientists noticed FAW infestation on sorghum and bajra (millet) in the fields of an agricultural research station at Ananthapuramu in Andhra Pradesh in October 2018. The researchers noted that the pest was gradually spreading to other millets grown in Ananthapuramu district.

In another report, researchers from Maharashtra noted FAW’s presence in sugarcane and sorghum. A  statement by the Ministry of Agriculture and Farmer Welfare on June 25 confirmed FAW infestation on sorghum and ragi (finger millet). The only consolation of sorts is that the spread in these crops has not been as rapid as than in corn.

Stopping FAW’s march

In 2018, when the pest attack first started, most farmers were unfamiliar with FAW. On Plantix, an AI-based farmer assistance mobile application where farmers can ask questions, farmers in 2018 were mostly asking to identify the pest, according to Sairekha Kadirimangalam, who works for Plantix in Hyderabad. However, as FAW starting spreading in India, the nature of queries changed. Maize farmers are now looking for solutions to stop the pest from damaging the crop, Kadirimangalam said.

There is no silver bullet to stop FAW in its tracks. A good monitoring system and farmer awareness about the pest are the first steps, said Chaudhry. “Sometimes, when confronted with the pest suddenly, farmers tend to panic and spray their fields with an array of chemicals,” she said. “This panic response is not just ineffective but also leads to broad-spectrum resistance in the pest, and should be avoided.”

“The first thing they (farmers) should do is to contact the nearest Krishi Vigyan Kendra (agricultural extension center) or state department’s agriculture officials,” said A.N. Shylesha, principal scientist, Entomology, NBAIR. Based on geography and extent of infestation, ICAR recommends a variety of solutions, which include mechanical, biological and chemical measures. For example, the infestation is in its early stages can be controlled by using bio-control agents like Trichogramma and Telenomus, and providing good nutrition to the plants. It is only when the infestation is severe that chemicals are recommended.

As FAW continues its march across India and other Asian countries, the need for effective protective measures will only grow stronger. “Increasing monoculture of maize around the year and wrong pest management practices with excessive dependence on chemical pesticides, which increased the resistance in the insect to pesticides, have contributed to FAW becoming a serious pest,” said G.V. Ramanjaneyulu, executive director of the Centre for Sustainable Agriculture, which works with smallholder farmers. “Any pest is always a function of practices followed and local weather conditions. Therefore, a shift towards agro-ecological approaches like non-pesticidal management, organic or natural farming, and multiple cropping systems are the ways to manage such pest outbreaks.”

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American attitudes toward agricultural gene drives

The first national survey inquiring about American attitudes toward agricultural gene drives — genetic modification techniques that can be used to “drive” a genetic trait or characteristic through a given insect pest population to help commercial crop production by squelching harmful pest effects — shows more support for systems that are limited in scope and aimed at non-native insects.

The survey of more than 1,000 American adults, conducted by researchers at North Carolina State University and the University of Wisconsin-Madison, can help inform further development of these gene drive systems in agriculture, an important consideration as the speed of technological development outpaces public understanding of the issues surrounding the technology.

Zack Brown, assistant professor of agricultural and resource economics at NC State and the corresponding author of a paper describing the research, said that people were more apt to support gene drive systems that controlled the spread of the drive. He added that respondents also more strongly favored gene drives targeting non-native species; they had a harder time supporting genetic changes to native insects. More than 50% of respondents supported controlled gene drive systems targeting non-native species.

Respondents also showed greater levels of support for gene drive systems that genetically alter an insect but leave it in the environment — taking away its ability to carry a pathogen causing a crop disease, for example — than systems meant to suppress or eradicate insect populations, although those differences were not large.

Nearly 50% of respondents opposed uncontrolled gene drive systems that would eliminate native species, with another 25% showing neither opposition nor support.

“This is valuable information for scientists because controllability is difficult to design in gene drive systems,” Brown said.

Other survey findings included increased opposition to gene drive systems among people who seek out food labeled non-genetically modified. Interestingly, though, their support exceeded opposition for limited gene drive systems targeting non-native species.

The research arose from a 2016 National Academies report that recommended gene drive research continue in parallel with ecological risk assessment and engagement with stakeholders and the public. Brown, lead author Michael Jones and coauthors realized that there was little to no published research on public perceptions of gene drive technology in an agricultural context.

“This is the right time — while the technology is still under development and before any release decisions have been made — to gain insights into what the public thinks, what types of information they prioritize from researchers, and who is trusted to carry out this sensitive research,” said Jones, an NC State Ph.D. candidate in agricultural and resource economics. “Proactively incorporating this feedback into technology design and risk assessment helps align the science with public values and the needs of diverse economic ecosystems.”

The process began with in-person, open-ended discussions about gene drive technologies and their possible uses and drawbacks with groups of consumers recruited from grocery stores. This method of conducting focus group discussions helped identify and distill the most important questions to be asked in the Web survey questionnaire.

Jason Delborne, associate professor of science, policy and society at NC State and co-author of the study, contributed to the design of the focus groups. “The focus groups provided a space for real conversations, where regular consumers learned about the potential for applying gene drives in agriculture and explored together their hopes and concerns. Inclusive deliberation about emerging technologies is a key foundation for responsible innovation,” he said.

The researchers used a Web-based questionnaire that allowed glimpses into how respondents interacted with information presented on gene drive systems and available FAQs. Jones said respondents spent a great deal of time looking through information when compared with other surveys.

“Maybe the fact that respondents went through a lot of research on our Web-based survey gave them a more nuanced perspective,” Brown says. “That seems to be reflected in the survey responses.”

The study also showed public perceptions on which organizations to trust with research into gene drive systems. Universities and the U.S. Department of Agriculture were the most trusted, with more than 60% calling those organizations very or somewhat trustworthy. Respondents were less trusting of foreign universities and the U.S. Dept. of Defense; small and large private companies were least trusted.

“The public wants a trusted body to be a leader here,” Brown said. “In this case, it’s American universities and the USDA.”

Powdery mildew biocontrol agents (BCAs)

IMAGE: The big photo shows cucumber leaves infected with powdery mildew, while the small close-up exhibits a few powdery mildew spores (from the powdery mildew colonies shown on the big photo),… view more 

Credit: Márk Z. Németh, Alexandra Pintye, Áron N. Horváth, Pál Vági, Gábor M. Kovács, Markus Gorfer, and Levente Kiss…

St. Paul, MN (September 2019)–Powdery mildew is a common fungal disease that infects many plants around the world, absorbing their nutrients and weakening or even killing them. In turn, powdery mildews are often attacked in the field by even smaller mycoparasites (fungi that feed on other fungi).

These mycoparasites penetrate the powdery mildews on the host plant surface and live inside of them, reducing or even stopping the harmful effects of the powdery mildew. Because of this, some strains of these mycoparasites (which belong to the genus Ampelomyces) are used as commercialized biocontrol agents (BCAs) of powdery mildews. There have been concerns about the environmental impact of the usage of these BCAs as little is known about the interactions between mycoparasites and powdery mildews.

To address environmental concerns, and to better understand these interactions, a group of scientists working at the Hungarian Academy of Sciences, the Austrian Institute of Technology, and the University of Southern Queensland (Australia) genetically modified two strains of the mycoparasite to express Green Fluorescent Protein (GFP). As a result, the mycoparasites emit green light when examined with a fluorescence microscope, enabling researchers to better understand their structures and functions. This is the first study to explore these interactions with fluorescent protein biotechnology.

Their research revealed that these mycoparasites can live up to 21-days on mildew-free host plant surfaces, where they can attack powdery mildew structures as soon as they appear. Also of note, this research showed that these mycoparasites cannot spread in sterile soil or in decomposing leaves on the ground, showing that concerns about the potentially negative environmental impact of the BCAs are largely unsubstantiated.

These results, which can be found in “Green Fluorescent Protein Transformation Sheds More Light on a Widespread Mycoparasitic Interaction” published in the August issue of Phytopathology, present the first successful genetic transformation of a group of common mycoparasites that have also been used as a BCA of an important group of crop pathogens. They are important for both biocontrol studies of crop pathogens and the ecology of natural interfungal parasitic relationships.


About Phytopathology

For more than 100 years Phytopathology™ has been the premier international journal for publication of articles on fundamental research that advances understanding of the nature of plant diseases, the agents that cause them, their spread, the losses they cause, and measures used to control them. Articles are characterized by their novelty, innovativeness, and the hypothesis-driven nature of their research.

Follow us on Twitter @Phytopathologyj and visit to learn more.

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Date palms attract two types of growth-promoting bacteria to their roots

Date palms attract two types of growth-promoting bacteria to their roots

From PestNet Community Digest


KAUST scientists wanted to know the factors that determine which bacteria associated with the roots of cultivated date palm trees. Credit: Ramona Marasco

Bacterial DNA sequencing analyses show date palms that are cultivated over a vast stretch of the Tunisian Sahara Desert consistently attract two types of growth-promoting bacteria to their roots, regardless of the location. This finding could help with improving crop cultivation in a warming climate.

Many factors influence which growth-promoting bacteria associate with , including , plant community diversity, applied and . Research conducted on shows that different types of wild plants attract different growth-promoting bacteria depending on their needs. Studies on conventional agricultural ecosystems have shown plant-root-bacteria associations vary according to the type of soil and the agricultural practices applied. Another KAUST study recently found that the roots of speargrass growing in the Tunisian desert aren’t picky at all: they attract whatever growth-promoting bacteria they can find in the surrounding resource-poor sand.

“But what happens in ecosystems where features of natural and agricultural environments converge, like in desert oases?” asks KAUST graduate Maria Mosqueira. “Under a climate change scenario, it is important to understand the role of microorganisms in arid ecosystems,” she explains.

Mosqueira, and colleagues working with Daniele Daffonchio, conducted microbiome analyses to identify the types of bacteria associated with the roots of cultivated Deglet Nour date palms in seven oases distributed over a vast 22,200 kilometer square stretch of the Tunisian Sahara Desert. The oases were located in contrasting environments: on the seacoast, in the mountains, among sand dunes and in the saline soil regions of the northern edge of the Tunisian Sahara Desert. Analyses of the ribosomal RNA gene were also conducted to test for the types of bacteria present in the surrounding sand/soil.

The team found that the Sahara palm tree roots consistently associated with two types of bacteria. Credit: Ramona Marasco

They found that the soil directly attached to the date palm roots was significantly modified compared to the surrounding “bulk” soil. And even though the dominant bacterial species in bulk soil varied from one location to another, date palm roots consistently chose to associate with the same two types of bacteria: Gammaproteobacteria and Alphaproteobacteria. These provide important services to the date palms—they promote the secretion of an important plant growth hormone and provide a protective effect against stresses like drought.

“We hope that our study will lead to other microbial ecology studies on desert oasis ecosystems; one of the most productive, yet unique, agroecosystems,” says Mosqueira.

The research group has several existing projects investigating and their associated microbiomes. A future focus will be to better understand the molecular interactions between plant roots and microbes as well as find ways to apply this knowledge to provide protective and nutritional services to agricultural crops grown in arid regions.

Desert bacteria protect food crops from salt toxicity

More information: Maria J. Mosqueira et al. Consistent bacterial selection by date palm root system across heterogeneous desert oasis agroecosystems, Scientific Reports (2019). DOI: 10.1038/s41598-019-40551-4

Bug smuggling | Global Plant Protection News

He discovered that Lapkiewicz had a track record in the U.S. too. Two months earlier, emperor scorpions and giant African millipedes from Tanzania had escaped from a package addressed to Lapkiewicz on a postal service delivery truck. (An exterminator killed the animals.)

Around the same time, Bessey says he learned that Lapkiewicz was selling spiders, millipedes, and emperor and dictator scorpions on Facebook. The criminal complaint alleges that Lapkiewicz was instructing suppliers to mislabel boxes to evade customs officers. “It showed this was part of an ongoing commercial enterprise,” Bessey says.

Lapkiewicz didn’t respond to multiple Facebook messages from National Geographic requesting an interview, and his lawyer didn’t respond to emails and a voicemail.

It’s illegal to import most insects and other arthropods, including spiders, scorpions, and millipedes, or their parts, into the U.S. without a permit from the Fish and Wildlife Service. The U.S. Department of Agriculture also requires a permit to bring in some live invertebrates. Emperor scorpions and dictator scorpions require special paperwork because they’re listed by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), an international agreement that regulates cross-border sales of species.

Then three years later, in 2018, U.S. customs officers in Indiana seized about a dozen giant African millipedes from a Lapkiewicz-bound package labeled “Plush Toys for my Friends Child about to be born,” according to the criminal complaint. A couple of weeks after that, wildlife inspectors at New York’s John F. Kennedy Airport opened a shipment addressed to Lapkiewicz to find 245 small cylinders containing the egg sacs of orchid mantises, pink and white insects from Southeast Asia that look like flower petals.

In August 2018 the U.S. District attorney’s office charged Lapkiewicz with smuggling wildlife and false labelling—federal crimes that carry a collective maximum of 25 years in prison. Lapkiewicz pleaded guilty to smuggling wildlife only. He was sentenced on July 2, 2019, to six months home confinement and four years probation.

“I knew at the time that there was a market for invertebrates,” says Bessey, who had worked as an agent for five years before investigating Lapkiewicz. “I really didn’t realise how large the market was until this case.”

Cockroaches—“great pets”

Demand for what most of us may think of as creepy crawlies—live as exotic pets or preserved as collectors’ treasures—has fueled a massive trade in everything from beetles and stick insects to tarantulas and scorpions. People even want cockroaches, the creature that once made me flee my apartment for 24 hours after finding one skittering around the shower. They make “great pets,” says Carlos Martinez, the owner of Reptile Factory, a pet shop based in Southern California.

Many insects and other arthropods are captive bred or otherwise sold in accordance with the law, but a global black market flourishes alongside the legal trade. It’s a little known corner of the illegal wildlife trade, a multibillion-dollar industry associated more with rhino horn and elephant ivory than the tiny creatures that can terrify us.

“A lot of things you find in the trade haven’t been legally exported from the area of origin or legitimately imported from the destination country,” says Stéphane De Greef, an environmental engineer and insect enthusiast from Belgium who runs a popular entomology group on Facebook. “It’s sadly very common.”

News stories of bug skulduggery abound. Take, for example, the Czech national fined in 2017 for attempting to smuggle 4,226 beetles, scorpions, spiders, and other invertebrates out of Australia. And the 7,000 spiders, insects, and other invertebrates stolen from the Philadelphia Insectarium and Butterfly Pavillion last year in a suspected attempt to sell them into the pet trade.

There’s no centralised database of seizures, which means there’s no way to estimate the global scale of the illegal trade. But Fish and Wildlife Service data obtained by National Geographic show that authorities in the U.S., a major demand country, seized at least 9,000 live and dead arthropods (not including crustaceans) that were being brought into the country for commercial purposes between June 2018 and June 2019. This likely represents a fraction of the total number of smuggled arthropods, which are easy to conceal in suitcases and shipping boxes.

Many countries ban or require special permits for the capture and export of certain species or species in particular areas, such as national parks, but that hasn’t stopped people from snatching little critters from the wild. Some people take them to keep or study. Others collect them to sell regionally as food. When it comes to the global commercial trade, poaching afflicts tropical countries in particular, where warmth and a plentiful food supply give rise to jumbo-size insects that explode with colour. Buyers around the world are willing to pay hundreds, even thousands, of dollars apiece for the rarest, flashiest, or otherwise most distinctive creature to breed or display alive or framed in their living rooms.

Scientists worry about the effects of the collecting craze on these small animals, which can be vital to food chains by pollinating crops and recycling nutrients back into the soil. “Whenever you take a large-scale collection of a single species and you extirpate it, or remove it, from an environment, you’re going to impact that ecosystem in one way or another,” says Floyd Shockley, who manages the insect collection at the National Museum of Natural History, in Washington, D.C.

Going to the fair

If there’s anyone who knows about the market for invertebrates, it’s Brent Karner. He’s the division manager for BioQuip Bugs, a company based in Rancho Dominguez, California, that offers preserved and live insects and other arthropods.