Pests & Diseases

February 2023 Pests & Diseases

Image from Twitter

Bananas: Expiration Date in Sight

Writing in the Laidback Gardener, biologist Audrey Martel warns of the demise of the Cavendish banana. She notes that artificial banana flavour tastes unlike the bananas we eat today because it was modelled on a variety that has now almost disappeared, the Gros Michel banana from Martinique. Sugars in the Gros Michel were so intense they formed a honey-like syrup. Today’s Cavendish banana was developed by William Cavendish and Joseph Paxton in 1835. Wild bananas, of which there are about 200 species, are often inedible, containing many hard seeds and very little flesh. Wild bananas reproduce sexually, which means more genetic mixing and diversity. The Cavendish banana is reproduced by cloning so each plant is an exact genetic replica of every other plant. This lack of genetic diversity was good for stability of what became an important agricultural crop, but bad in terms of that crop’s resilience to pests and diseases. At the end of the 20th century, the fungus Fusarium oxysporum attacked Gros Michel bananas, killing almost all the banana trees. A few crops in isolated areas were saved, but the Cavendish, more resistant to the fungus, replaced it in world production. Now, however, another strain of Fusarium called TR4 that can kill many varieties, including the Cavendish, is spreading to more and more countries. In many places bananas are a staple crop, so this fungus is a threat to food security as well as livelihoods. A team of scientists has found that exposing plants to another variant of Fusarium provides protection for up to 10 days, but this solution may not be commercially viable, or permanent. We may have to go back to wild variants to breed a new banana.

Researchers from AU Flakkebjerg have studied how plants can keep pests, diseases and fungi at bay by secreting certain substances. This could be used as a plant defense of the future. Credit: Enoch Narh Kudjordjie.

Plant protection of the future may come from the plants themselves

In happier news, researchers from AU Flakkebjerg, Denmark, have studied how plants with different resistance traits interact with their microbes to respond to pathogen attack. The research is published in the journal Microbiology Spectrum. To begin with, the researchers infected two-week-old Arabidopsis genotypes growing in field soil in a greenhouse with the fungal pathogen Fusarium oxysporum, the same culprit that threatens bananas. Then they studied the results. Enoch Kudjordjie explains, “… we were absolutely sure that the plants were actually infected. The qPCR test showed a clear difference between the two genotypes, with the resistant genotype having a much lower level of the pathogen than the susceptible one.” They then continued to explore the differences between the chemistry and microbiomes in the two genotypes, and found large differences. The plant metabolites and hormones studied were distinct in both the healthy and diseased plants, confirming the involvement of certain plant chemical molecules in mediating plant defense. Likewise, they found that microbial composition, as well as microbial community networks, were distinct in healthy and diseased resistant and susceptible plants. Moreover, beneficial bacteria such as the genera Pseudomonas and Rhizobium were mostly enriched in the rhizosphere of infected plants, suggesting an active recruitment of microbes to resist pathogen invasion. This work has deepened our understanding of how plants defend themselves against a fungal pathogen. More importantly, we found a strong and unique association between individual defense metabolites and specific microbes in the healthy and diseased plants of the different genotypes. “These results strongly confirmed that three underlying host components (genes, metabolites and microbiomes), interactively control the plant defense,” explains Kudjordjie. They also suggest a future where plants are cultivated with optimized yield and other agronomic and economic gains without the use of synthetic chemicals.

Mosaic Diseases Caused by Potyviruses. Image from University of California.

Copying nature to help plants resist viruses

CRISPR gene editing is opening up exciting new frontiers in crop research. The CRISPR-Cas9 technique makes it possible to modify a region of the plant’s DNA in a targeted and precise manner, allowing desirable traits, such as disease resistance, to be retained while eliminating undesirable traits. An iterative gene-editing strategy was recently studied to help tomatoes develop better resistance to a several plant viruses. The findings are published in the Plant Biotechnology Journal.

Biodiversity Citizen Science Conservation Miscellany Pollinators, Molluscs and Other Invertebrates

December 2022: Pollinator & Invertebrate Round-up

Image courtesy of Empress of Dirt

‘Bees get all the credit’: slugs and snails among 2023 Chelsea flower show stars: Stag beetles and hornets will be among the stars of Chelsea flower show next year as horticulturalists encourage people to welcome invertebrates into the garden. Bumblebees and butterflies tend to get a lot of press, but in a 2023 garden sponsored by the Royal Entomological Society, less glamorous creepy-crawlies will take centre stage. The garden may startle those used to more pristine spaces, as it will feature rotting wood and leaves as habitat for beetles and other insects, but it will still include a vast array of native and non-native flowering plants, which will be there to encourage pollinators. It will highlight how pollination, food security and preventing vector-borne diseases are critical to our survival in a changing world and that insect conservation is often undervalued compared with mammal and bird conservation. [Editor’s note: this article includes tips on insect-friendly gardening.]

(A) Overall view of the experimental setup during training. The wooden box was covered by a transparent cover, which allowed observing the behavior of the bees accessing the inner compartments. After passing the first inner compartment, the focal bee faced a training stimulus placed in the middle of the back wall. An Eppendorf tip delivered sucrose solution in the middle of the image. (B) Overall view of the experimental setup during a test. After passing the first inner compartment, the focal bee faced two lateral walls displaying the same test alternative on each side. The test stimuli were novel to the trained bee, i.e. they were never experienced during the training. No reward was provided during the test. The first choice and the cumulative choices performed during 40 s were recorded. (C) Examples of stimuli used in the first and second experiment. (D) Stimuli used in the third experiment. (E) Examples of stimuli used in the fourth experiment. Credit: Proceedings of the National Academy of Sciences (2022). DOI: 10.1073/pnas.2203584119

Honeybees use a ‘mental number line’ to keep track of things: A small team of researchers with members from the University of Toulouse, the University of Lausanne and the University of Padova has found evidence that honeybees have a mental number line in their tiny brains. In their paper published in Proceedings of the National Academy of Sciences, the group describes experiments they conducted with captive honeybees. Prior research has suggested that in to addition humans, baby chickens possess what scientists call a mental number line. Numbers of things are represented in the brain and are processed in a left-to-right direction. For example, when most people are asked to sort piles of grapes by the number, most do so from left to right, with the smallest pile on the left. In this new effort, the researchers wondered whether honeybees might also use a mental number line to keep track of things. To find out, they conducted a two-stage experiment.

Credit: N. Gamonal, Didde Sørensen

Following insect ‘footprints’ to improve crop resilience and monitor pollinator biodiversity: Bees and other insects leave behind tiny “footprints” of environmental DNA on plants each time they visit, giving researchers a way of tracking where insects have been, and offering clues on how to help them flourish. A team of researchers, including the Wellcome Sanger Institute and led by the University of Copenhagen, have used these DNA footprints as a non-invasive way to collect information on insect biodiversity, giving new insight into how to boost pollination and protect insect biodiversity and crops against threats such as climate change. The new study, published in Environmental DNA, is the first time DNA footprints have been used alongside visual observations to track the kind of insect visitors to crops, helping to see if there are any pests and informing new ways to encourage beneficial insects. Didde Hedegaard Sørensen, laboratory technician and an author from the University of Copenhagen, Denmark says, “The exciting thing about this study is that it can have an immediate, real-world impact on agricultural systems. Our results can assist farmers in managing their crops against the rising threats of reduced pollinators. Environmental DNA can be used to investigate the biodiversity in agricultural landscapes beyond apple orchards, making it a fast and non-invasive way to gain more knowledge about the world around us.”

AI rendering bees and electricity. Credit: Ellard Hunting

Insects contribute to atmospheric electricity: By measuring the electrical fields near swarming honeybees, researchers have discovered that insects can produce as much atmospheric electric charge as a thunderstorm cloud. This type of electricity helps shape weather events, aids insects in finding food, and lifts spiders up in the air to migrate over large distances. The research, appearing in the journal iScience, demonstrates that living things can have an impact on atmospheric electricity.

Credit: CC0 Public Domain

California county sees highest number of monarch butterflies in more than 20 years: There’s some hope fluttering around San Luis Obispo County this holiday season. It comes in the form of an iconic orange-and-black striped butterfly that makes tall eucalyptus or Monterey cypress trees its home up and down the coast. More than 129,000 western monarch butterflies were counted in the county by Xerces Society for Invertebrate Conservation employees and volunteers in November, according to preliminary data shared by local volunteer coordinator Jessica Griffiths. That’s the most counted in San Luis Obispo County in more than 20 years—in 1998 there were about 182,000 counted, according to the Xerces Society’s data. The numbers are giving some researchers hope that the western monarch butterfly population could be rebounding from devastatingly low numbers a few years ago that left some worrying the insect was on the verge of extinction.

Arizona’s state butterfly, the two-tailed swallowtail butterfly, can be found at Tucson-area botanical gardens. Credit: Jeff Oliver/University Libraries

Botanical gardens are ‘hot spots’ for butterflies amid climate change: Despite their relatively small footprint in urban areas, botanical gardens are important hotspots for butterfly biodiversity in the arid Southwest, according to a new study by University of Arizona scientists published in the journal Insects. Using more than 10,500 community science observations spanning roughly 20 years, researchers compared butterfly species richness and diversity in botanical gardens versus in the gardens’ surrounding metropolitan areas. The study focused on five large, urban cities in the Southwest, including Tucson and Phoenix in Arizona; Palm Desert, California; Albuquerque, New Mexico; and El Paso, Texas. Each city averages less than 11 inches of precipitation annually and, with the exception of Palm Desert, each has a population over 500,000 residents. While botanical gardens represent less than 1% of metropolitan landscapes—between 0.002–0.22% on average—these urban green areas have disproportionately high butterfly species richness and diversity compared to the much larger surrounding city areas. In fact, species richness in these gardens scored in the 86th percentile or above, according to the study.

Screen grab from YouTube video.

These bumblebees like playing and it’s the sweetest thing: Playing is an important behavior in humans — it helps us learn new skills, improve control over our bodies, and also helps with bonding. In other mammals, play has also been documented as an important behavior — but in insects, playing has been far less studied. For Lars Chittka, a behavioral ecologist at Queen Mary University of London (QMUL), peering into the minds of bees has been a long-term interest. Chittka recently published a book called the Mind of a Bee, where he highlights many of the remarkable findings about the intellect and behavior of bees. But this new study came almost by accident. Chittka and his team were looking at how bumblebees learn complex behaviors. In a scientific setup, bees had to move wooden balls, and if they moved them to the right place, they got a sweet reward. But the researchers started noticing how some bees would just push the balls around even without any reward. This was puzzling, so the researchers started looking at this in more detail. The study followed 45 bumblebees in an arena who chose between walking through an unobstructed, clear path and reaching a feeding area and deviating from this path to fiddle with wooden balls. There was no advantage to rolling the balls, and there is no analogue behavior in the wild that would prompt bees to roll the balls. Still, all individual bees rolled the balls between 1 and 117 times — a strikingly large number that strongly suggests the bees found pleasure in this activity. Note article includes 1:30 video from the BBC that shows the bees playing with wooden balls. (See also: First-ever study shows bumble bees ‘play’)

Screen grab from YouTube video showing leafhopper baby “Mildred” in her new dress.

True Facts: Leafhoppers and Friends

This 5-minute video features stunning macro shots of tiny leafhopper  babies with scientifically accurate and hysterically funny commentary. You’ll never look at leafhoppers quite the same way again! Thanks to reader Carol English for sharing.