New research decodes plant defense system, with an eye on improving farming and medicine

Findings reveal new genetic links between plants' circadian clock and immunity systems

Date: June 13, 2019 Source: University of Maryland Baltimore County Summary: The plant circadian clock determines when certain defense responses are activated (often timed with peak activity of pests), and compounds used in defense affect the clock. New findings show how the clock regulates stomata opening/closure for defense, and how the defensive compound jasmonic acid influences the clock. This could lead to plants that are better at defending themselves, reducing the need for pesticides, and potentially influencing timing for human medical treatment.

UMBC's Hua Lu, professor of biological sciences, and colleagues have found new genetic links between a plant's circadian rhythm (essentially, an internal clock) and its ability to fend off diseases and pests. The findings were 10 years in the making and published in Nature Communicationsthis week. The results could eventually lead to plants that are more resistant to disease-causing pathogens and better treatment for human diseases.

"It's quite cool," Lu says, "because, in both plants and animals, people are beginning to study the crosstalk between the circadian clock and the immunity system."

Timing is everything

In response to daily attacks from bacteria, fungi, and other pests, plants have evolved various strategies to protect themselves. Plants may close their stomata -- small openings in the waxy coating on their leaves -- to prevent entry by some bacteria. They might produce chemicals such as salicylic acid and jasmonic acid to repel bacteria and insects. They also make a large number of proteins that are important for successful defense.

Actions like closing stomata, producing salicylic acid, and more happen on a daily schedule, often peaking at the times when certain pathogens and pests are most likely to be active. The rhythmic nature of plant defense suggests plants are coordinating their internal clock with their defense system to increase the effectiveness of their defensive actions.

In this study, Lu and colleagues found for the first time that LUX, a central gene in the plant circadian clock, is important for regulating the opening and closing of the stomata at specific times of day, and also for activating defense mediated by salicylic acid and jasmonic acid.

In a typical plant, the stomata open during the day, to enable exchange of gases required for photosynthesis. Then they close at night, to prevent water loss. The stomata also close in response to daytime pathogen attacks. They respond minimally to an attack at night, because they're already closed.

However, in plants with a non-functional version of the LUX gene, Lu found that the stomata are open both day and night. During a daytime attack, the stomata stay open wider than normal plants. During a nighttime attack, though, some of the stomata close. This means that plants lacking a functional LUX gene have less control over when their stomata open, allowing more opportunistic pathogens to get in. This distinction indicates that LUX is critical for the timing of the stomata-driven defense response, tying defense to the circadian clock in a new way.

Lu's research also dives into the relationship between the LUX gene and the defense chemicals salicylic acid and jasmonic acid. While it was known that the circadian clock can regulate defense responses, this paper shows that the reverse is also true: "A properly tuned circadian clock is important for defense activation. When defense is activated, it then can feed back to regulate the circadian clock," Lu says.

The research team specifically showed that the presence of LUX is needed for normal jasmonic acid signaling. In turn, jasmonic acid also affects expression of LUX and the circadian clock. This reciprocal regulation between the circadian clock and defense signaling helps plants balance their energy use for normal growth and development and defense responses.

From farms to pharma

Lu is interested in pursuing further research to figure out how timing influences the plant defense system. How does the circadian clock affect multiple aspects of defense responses? What molecules from pathogens and pests interfere with a plant's circadian clock and subsequently limit its ability to protect itself? Better understanding how clock genes control plant defense and how pathogens interact with plant defense systems could benefit agriculture and beyond.

"Pathogens are everywhere all the time. Often the most active form of a pathogen varies during a day. Also, plants could have different defense strategies at different times of day," explains Lu. "So, when is the best time to apply pesticides? That could depend on the pathogen, its infection mode, and the behavior of your crop plants. I think that field tests are needed to figure out the best time to apply chemicals to achieve the most efficacy in preventing infection or the spread of infection."

Less pesticide use overall would reduce runoff of chemicals into waterways and lower costs for farmers. Reduced use of antibiotics could help stem antibiotic resistance, which would benefit humans, too.

Plus, plants aren't the only ones whose immune system activity fluctuates throughout the day. Animal systems also have daily cycles. So, "similar ideas can be applied to the medical field," Lu says.

There are similarities between the ways plants and animals interact with their pathogens and pests at the molecular level. Maybe in the future, your prescription will come with specific timing instructions, or your surgery will be scheduled based on your immune system activity.

Science in action

Lu says all of her research, and this multi-part paper in particular, is driven by her lab members. "It's great to work with this many dedicated people," she says. "Without them, I couldn't do it."

That includes postdoctoral fellow Chong Zhang, who is now employed by the USDA, and current postdoc Min Gao, who are co-first authors on the new paper. Five undergraduate students and a high school student also contributed to this long-term project. Some of the experiments required testing every four hours over a 24-hour period, which meant someone was sleeping on a couch in the lab when they were underway.

Overall, Lu's team members are driven by the potential benefits their work could contribute to society. They are excited by the prospect of improving crop yields to feed a growing population, reducing pollution, or reducing side effects for human medical treatment through improved timing and dosing.

"This field interests me because I can see my work have some practical applications, and I think that's important," Lu says. "That should be every scientist's goal -- to use your knowledge in real life."

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Journal Reference:

Chong Zhang, Min Gao, Nicholas C. Seitz, William Angel, Amelia Hallworth, Linda Wiratan, Omar Darwish, Nadim Alkharouf, Teklu Dawit, Daniela Lin, Riki Egoshi, Xiping Wang, C. Robertson McClung, Hua Lu. LUX ARRHYTHMO mediates crosstalk between the circadian clock and defense in Arabidopsis. Nature Communications, 2019; 10 (1) DOI: 10.1038/s41467-019-10485-6

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University of Maryland Baltimore County. "New research decodes plant defense system, with an eye on improving farming and medicine: Findings reveal new genetic links between plants' circadian clock and immunity systems." ScienceDaily. ScienceDaily, 13 June 2019. <www.sciencedaily.com/releases/2019/06/190613103122.htm>.

Interactions between plant and insect-infecting viruses

Date: June 13, 2019 Source: Boyce Thompson Institute Summary: Aphids and the plant viruses they transmit cause billions of dollars in crop damage every year. Researchers are examining this relationship at the molecular level, which could lead to new methods for controlling the pests. The researchers uncovered what may be the first example of cooperation between a plant virus and an insect virus to increase their likelihood to spread.

Aphids and the plant viruses they transmit cause billions of dollars in crop damage around the world every year. Researchers in Michelle Heck's lab at the USDA Agricultural Research Service and Boyce Thompson Institute are examining the relationship at the molecular level, which could lead to new methods for controlling the pests.

Heck's group used recently developed small RNA sequencing techniques to better understand how plant viruses interact with aphids. In an unanticipated discovery, Heck and her team uncovered what may be the first example of a plant virus and an insect virus cooperating to increase the likelihood that both viruses will spread to other plant and aphid hosts.

The work was published in the May 22 issue of Phytobiomesjournal. The researchers focused on the green peach aphid (Myzus persicae), which transmits more than 100 different plant viruses and feeds on a wide variety of crops, including peaches, tomatoes, potatoes, cabbage, corn and numerous others.

Potato leafroll virus (PLRV) is of particular concern because it can reduce potato yield by more than 50%, causing 20 million tons of annual global yield losses.

"The most interesting finding of this research is that PLRV suppressed the aphid's immune system, and this suppression was mediated by a single virus protein, the P0 protein," says Jennifer Wilson, a co-first author on the paper. Wilson is a PhD candidate in the School of Integrative Plant Science (SIPS) at Cornell University and is conducting her thesis research with Dr. Heck.

P0 is a PLRV protein that is expressed inside plant tissue but not inside the aphids. While P0 had been previously shown to suppress plants' immune systems, the protein's impact on the insect's immune system was a surprise to the researchers.

"We don't know if the aphids ingest P0 from the plant or not, but we do know that when P0 is present in the plant, the aphids' immune systems are suppressed," explains Wilson.

One critical result of the insect's immune system being hampered is an increase in the proliferation of an insect virus, Myzus persicae densovirus (MpDNV). The researchers also found that aphids with more copies of MpDNV were more likely to have wings.

Because green peach aphids rarely have wings until the weather turns colder in the fall, this increase in winged insects could mean increased spread of PLRV and MpDNV to new hosts all summer long, a synergistic effect that wouldn't happen as much if the aphids were infected with only one of the viruses.

"We think we have found the first example of cooperation between a plant virus and an insect virus," Wilson says. "This cooperation may lead to increased transmission of both viruses."

Wilson and Heck are currently working to test this hypothesis by repeating the experiments in aphids not infected with MpDNV, which Wilson collected last summer from farms in upstate New York.

Future work could include figuring out how MpDNV and the P0 protein could be used to control virus transmission by aphids.

"Developing strategies to block virus transmission in the field is a major goal of our research program," said Heck, also an adjunct assistant professor in SIPS. "Wilson's thesis work is paradigm shifting. Stay tuned for more exciting stuff from her in the near future."

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Materials provided by Boyce Thompson Institute. Note: Content may be edited for style and length.

Journal Reference:

Patricia V. Pinheiro, Jennifer R. Wilson, Yi Xu, Yi Zheng, Ana Rita Rebelo, Somayeh Fattah-Hosseini, Angela Kruse, Rogerio Santos Dos Silva, Yimin Xu, Matthew Kramer, James Giovannoni, Zhangjun Fei, Stewart Gray, Michelle Heck. Plant Viruses Transmitted in Two Different Modes Produce Differing Effects on Small RNA-Mediated Processes in Their Aphid Vector. Phytobiomes Journal, 2019; 3 (1): 71 DOI: 10.1094/PBIOMES-10-18-0045-R

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Boyce Thompson Institute. "Interactions between plant and insect-infecting viruses." ScienceDaily. ScienceDaily, 13 June 2019. <www.sciencedaily.com/releases/2019/06/190613103142.htm>.

How poppy flowers get those vibrant colors that entice insects

Date: February 8, 2019 Source: University of Groningen Summary: With bright reds and yellows -- and even the occasional white -- poppies are very bright and colorful. Their petals, however, are also very thin; they are made up of just three layers of cells. Scientists used microscopy and mathematical models describing how light interacts with petals to find out how the vibrant colors are created. 

Different poppies which were used in the study. 

Credit: University of Groningen 

With bright reds and yellows -- and even the occasional white -- poppies are very bright and colorful. Their petals, however, are also very thin; they are made up of just three layers of cells. University of Groningen scientists Casper van der Kooi and Doekele Stavenga used microscopy and mathematical models describing how light interacts with petals to find out how the vibrant colors are created. The results will be included in a special edition of the Journal of Comparative Physiology A, which focuses on the relationship between insects and flowers. 

Van der Kooi's main research focus is the evolution of flower color, and the interaction between flower color and pollinators. This led him to investigate how petals produce their visual signals. He explains why the flowers of poppies (Papaver, Meconopsis and related species) are interesting: 'The common poppy is an extreme case, it has very thin petals that nevertheless cause a very high scattering of light. Poppies also contain high concentrations of pigments.' 

Jigsaw pieces 

The researchers collected petals from different poppy species and studied their structures using different techniques. They discovered that the pigment was only present in the two outer cell layers and not in the middle layer. The pigmented cells had a fascinating shape, with many invaginations that made them look like complicated jigsaw pieces. 'This creates many air-filled gaps between the cells, which cause the reflection of light on the cell/air boundary', says Van der Kooi. 

Furthermore, the petals contained huge amounts of pigment. 'They are among the highest concentrations that I have ever measured in any flower.' Indeed, the characteristic black markings at the center of some poppy flowers are caused by extreme concentrations of red pigment. Van der Kooi concludes that dense pigmentation together with strong scattering causes the striking poppy colors in the red parts of the petal. 

Sexual mimicry 

The new findings can be linked to previous work on poppy color evolution. Intriguingly, poppies in the Middle East reflect no ultraviolet light, while the same species in Europe do. This difference may be due to their preferred pollinators. 'In Europe, poppies are pollinated mostly by bees, which cannot see red very well; however, they will pick up ultraviolet.' In contrast, poppies in the Middle East are pollinated by beetles that do see red colors. 

'Moreover, previous studies have shown that the black spots at the heart of some poppies mimic the presence of a female beetle. This is a way for the flowers to attract male beetles. A case of sexual mimicry, as occurs in other plants such as orchids', explains Van der Kooi. 

Air gaps 

The next question will be how these jigsaw-like cells and the air gaps that cause the efficient scattering have evolved. 'These cell shapes are commonly present in leaves, so that might be a clue.' Furthermore, results suggest that poppies evolved ultraviolet signals when they began growing in more northern regions. It makes the evolutionary history of these brightly colored flowers an interesting object of study. 

The paper by Van der Kooi and Stavenga will be included in a special edition of the Journal of Comparative Physiology A, edited by Friedrich Barth (University of Vienna). This special edition, with the title "Insects and Flowers. New insights into an old partnership," is due to appear in print late this spring. The paper has already been published online. 

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Casper J. van der Kooi, Doekele G. Stavenga. Vividly coloured poppy flowers due to dense pigmentation and strong scattering in thin petals. Journal of Comparative Physiology A, 2019; DOI: 10.1007/s00359-018-01313-1

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University of Groningen. "How poppy flowers get those vibrant colors that entice insects." ScienceDaily. ScienceDaily, 8 February 2019. <www.sciencedaily.com/releases/2019/02/190208115304.htm>.

Recommending plants to benefit and attract pollinators

Date: November 14, 2018 Source: American Society for Horticultural Science Summary: Pollinating insects are integral to the health of all terrestrial ecosystems and agriculture worldwide. As homeowners attempt to conserve pollinators through horticulture practices, they often seek the advice and guidance of horticulture retail employees regarding what plants they can successfully include on their properties to maximize their intended benefit to pollinators as well as to their home ecosystems.

A survey was conducted by the University of Nebraska to unveil the extent to which horticultural employees are knowledgeable about pollinators. Carter Westerhold, Samuel Wortman, Kim Todd, and Douglas Golick sought to determine what plant and management recommendations these employees were passing along to customers regarding pollinator conservation and to assess what other advice could be added to their repertoire of recommendations to augment their general benefit.

Their findings were published in the article "Knowledge of Pollinator Conservation and Associated Plant Recommendations in the Horticultural Retail Industry" in HortTechnology.

As detailed in the article, pollinating insects are integral to the health of all terrestrial ecosystems and agriculture worldwide. Urbanization can greatly reduce nutritional resources and habitat for pollinators. However, these losses can be mitigated through targeted landscape practices, such as planting nectar- and pollen-rich plants and managing pollinator habitats in urban areas, especially in home landscapes.

As homeowners attempt to conserve pollinators through horticulture practices, they often seek the advice and guidance of horticulture retail employees regarding what plants they can successfully include on their properties to maximize their intended benefit to pollinators as well as to their home ecosystems.

The researchers discovered at the outset that overall employee knowledge was adequate. However, among uncertified and part-time employees, knowledge and awareness was significantly lower, especially related to the breadth of possible plant selection. Due to that evident information gap, the researchers identified several opportunities for educational outreach aimed at improving both employee and customer understanding on this important subject.

Results and determinations of this survey were extrapolated and generalized from its 224 respondents used as a cross-section of horticulture employees nationally. Initial advice from these employees lacked uniformity, although the glaring variables there were often due to an understanding of the needs of localized ecosystems and were based on personal observations from each individual.

However, accurate knowledge of beneficial plants for pollinators proved to be the weakest topic for horticulture employees, signaling a need for specialized education and training to strengthen a verifiable transference of information.

The researchers also determined that more-detailed labeling of pollinator food plants would benefit this endeavor, as customers may purchase more pollinator-friendly plants when correctly labeled as "pollinator friendly." Also, they surmise that businesses could distribute information to customers on pollinator conservation in the form of pamphlets or booklets that focused on plant selection and landscape management.

Public interest in pollinator conservation has increased markedly in the past decade. The number of homeowners seeking pollinator conservation advice from horticulture retail businesses should rise as well. Knowledgeability of horticulture retail staff in plant selection is an important quality for a garden center to have. The results of this survey might help to determine how to better ensure that accurate information is being passed on to customers.

Westerhold adds "The home landscape could be an invaluable asset to pollinator conservation efforts. Our study highlights opportunities for extension and industry to ensure home pollinator conservation efforts are successful by equipping retailers with scientifically accurate information for homeowners."

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Materials provided by American Society for Horticultural Science. Note: Content may be edited for style and length.

Journal Reference:

Carter M. Westerhold, Samuel Wortman, Kim Todd, Douglas Golick. Knowledge of Pollinator Conservation and Associated Plant Recommendations in the Horticultural Retail Industry. HortTechnology, 2018; 28 (4): 529 DOI: 10.21273/HORTTECH03973-18

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American Society for Horticultural Science. "Recommending plants to benefit and attract pollinators." ScienceDaily. ScienceDaily, 14 November 2018. <www.sciencedaily.com/releases/2018/11/181114132011.htm>.

Relação de mutualismo entre figueiras e vespas tem nova fase revelada

08/08/2018

Por uma relação de mutualismo, onde não há vespas-do-figo, as figueiras não se reproduzem e vice-versa

Por Redação - Editorias: Ciências Biológicas

Estudo foi publicado em edição especial da Acta Oecologica com quatro artigos de pesquisadores da USP. Outro trabalho analisa diferenças morfológicas no ovipositor de diversas espécies de vespas parasitoides – Foto: Divulgação

A relação de mutualismo que existe entre a figueira e a vespa-do-figo é uma das mais fascinantes da natureza. Os dois têm a sua existência de tal modo entrelaçada que um não pode existir sem o outro. Onde não há vespas-do-figo as figueiras não se reproduzem e vice-versa.

O ciclo de reprodução das vespas-do-figo só ocorre no interior dos figos. Esses, ao longo de dezenas de milhões de anos de evolução, acabaram tão modificados devido à interação com aqueles insetos que hoje são confundidos com frutos. Mas figos não são frutos, são inflorescências invertidas. São invólucros que contêm em seu interior centenas de flores minúsculas que produzem sementes internamente graças ao trabalho de polinização proporcionado pelas vespas.

O ciclo de desenvolvimento das flores da figueira e de suas vespas é estudado como forma de entender a evolução do mutualismo. Ainda no fim dos anos 1960, quando esse mutualismo entre planta e inseto começou a ser elucidado, o ciclo de desenvolvimento foi dividido em cinco fases distintas (A, B, C, D e E). Elas descrevem tudo o que ocorre desde o momento em que a vespa mãe penetra no interior do figo para pôr seus ovos, até quando uma nova geração de vespas fêmeas fertilizadas emerge do figo para renovar o ciclo.

Meio século após a descrição inicial deste ciclo de desenvolvimento, o biólogo Luciano Palmieri Rocha, da Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto (FFCLRP) da USP vem agora propor a existência de uma nova fase, que ele denominou F, que trata das interações ecológicas que ocorrem após a saída das vespas, envolvendo os figos maduros que caem ao solo para apodrecer.

O estudo foi publicado na revista Acta Oecologica, em edição especial justamente em homenagem aos 50 anos da descoberta inicial do ciclo das figueiras e suas vespas. O trabalho teve apoio da Fundação de Amparo à Pesquisa do Estado de São Paulo (Fapesp).

A edição traz 20 trabalhos, sendo quatro deles de pesquisadores do Laboratório de Interação Inseto-Planta do Departamento de Biologia da FFCLRP da USP. O laboratório é chefiado pelo professor Rodrigo Augusto Santinelo Pereira.

“Na natureza, vemos muita competição, por isso chama a atenção a interação entre figueira e vespa-do-figo. As duas caminham juntas para se adaptar mutuamente e tentar sobreviver. Se uma morrer, a outra também desaparecerá”, disse Palmieri à Agência Fapesp.

Tal mutualismo não está restrito à interação entre a figueira (Ficus carica) que produz os figos comestíveis e suas polinizadoras específicas, as vespas-do-figo da espécie Blastophaga psenes. Existem mais de 750 espécies do gênero Ficus e, para cada uma delas, há uma espécie de vespa polinizadora da família dos agaonídeos.

É um mutualismo muito antigo, explica Palmieri. Os fósseis mais antigos de vespas-do-figo datam de 34 milhões de anos atrás. São muito semelhantes às espécies atuais, indicando que a relação simbiótica evoluiu cedo e não mudou fundamentalmente desde então. Evidências moleculares apontam que a relação existia há 65 milhões de anos, o que sugere que ela possa ser ainda mais antiga, ainda do tempo dos dinossauros.

“Foi quando os ancestrais das vespas-do-figo começaram a depositar ovos nas flores de figueiras ancestrais. São inflorescências que, acredita-se, ainda eram abertas e, portanto, aptas a ser polinizadas por diversos insetos”, disse o pesquisador.

Ao longo de pelo menos 65 milhões de anos de evolução, as inflorescências da figueira se tornaram invólucros fechados ao mundo exterior, onde apenas as vespas-do-figo conseguem penetrar.

“Inicialmente, as vespas começaram a parasitar as figueiras. Por algum mecanismo evolutivo desconhecido, a planta acabou por cooptar o parasitismo das vespas dentro de seu ciclo reprodutivo”, disse Palmieri.

O ciclo de desenvolvimento das flores da figueira e de suas vespas se inicia com a entrada da vespa mãe no interior do figo. “O figo é uma urna, que preserva e protege centenas de pequeninas flores. Pelo fato de as flores do figo se abrirem internamente, elas precisam de um processo especial para serem polinizadas. Não podem depender do vento ou das abelhas para transportar seu pólen. É aí que entra a vespa-do-figo”, disse.

No interior do figo há flores femininas e masculinas, que se desenvolvem em momentos diferentes. A fase A ocorre quando as flores femininas ainda não estão maduras. Pouco tempo depois, as flores femininas amadurecem e ficam prontas para serem fertilizadas. É quando os figos se tornam receptivos para receber as vespas e passam a exalar uma quantidade enorme de compostos voláteis, iniciando a fase B.

A agora denominada fase F inclui as interações ecológicas que ocorrem após a saída das vespas, envolvendo os figos maduros que caem ao solo para apodrecer – Foto: Divulgação

“São sinais químicos que servem para atrair apenas as vespas específicas que polinizam as flores daquela espécie de figueira. É tudo sincronizado”, disse Palmieri.

O figo não é inteiramente fechado. Existe um pequeno buraco, o ostíolo, que a vespa mãe deve atravessar para ter acesso ao interior do fruto. Ao fazê-lo, o inseto perde asas e as antenas se quebram de modo que, uma vez lá dentro, não tem como sair. Depois de botar os ovos, a vespa morrerá. “Ela precisa forçar sua entrada através do ostíolo. Depois que ela entra é mais difícil outras entrarem, mas não incomum”, disse.

Ações sincronizadas

Uma vez dentro do figo, a vespa mãe depositará ovos em inúmeras flores internas, mas não em todas. Ao fazê-lo, ao mesmo tempo a vespa mãe fertiliza as flores com o pólen que carrega depositado em bolsas polínicas localizadas abaixo das asas. As flores onde foram depositados os ovos se modificam, tornando-se estruturas endurecidas chamadas galhas.

Inicia-se então a fase C, que se estenderá pelos próximos dois a três meses. As flores polinizadas que não ganharam um ovo de vespa se transformam em sementes. Já as flores que receberam ovos e se modificaram na forma de galhas guardam em seu interior larvas de vespa.

A fase D ocorre no fim do período de incubação das larvas. É esse também o momento em que as flores masculinas começam a ficar maduras, abrindo e expondo estruturas chamadas anteras, onde fica o pólen.

“A abertura das flores masculinas é sincronizada com o fim do desenvolvimento das vespas. As primeiras a sair das galhas são as vespas machos, que não têm asas e olhos reduzidos, mas têm mandíbulas grandes e fortes. Os machos rastejam sobre as flores femininas até localizar as galhas onde estão as vespas fêmeas, suas irmãs, que estão prontas para emergir. Nesse momento, os machos fazem uso de um pênis telescópico que penetra e fecunda a fêmea dentro da galha. Feito isso, os machos começam a usar suas mandíbulas para abrir um buraco na parede do figo. Uma vez que o buraco é aberto, os machos caem no chão e morrem”, disse Palmieri.

A fase D termina com a emergência das vespas fêmeas de dentro das galhas. “Rastejando na direção do buraco, elas passam sobre as flores masculinas, coletando em bolsas o pólen com o qual polinizarão outras figueiras”, disse.

Uma vez que atravessam o orifício cavado pelos seus irmãos fecundadores, as fêmeas estão prontas para voar em busca de outras figueiras, recomeçando o ciclo. A fase E diz respeito à dispersão das sementes das figueiras.

“Uma figueira grande é capaz de produzir mais de 1 milhão de figos em uma florada. Os figos são alimento de macacos, roedores, morcegos, porcos-do-mato e muitos outros. Quase todos os animais vertebrados da floresta têm figos como parte da sua dieta. Ao comer os figos maduros que ainda pendem nos galhos ou que já caíram ao solo, os animais irão dispersar as sementes no meio ambiente através de suas fezes”, explicou Palmieri.

Fase F

Além das cinco fases do ciclo clássico de desenvolvimento de figueiras e das vespas, como vem sendo estudado há 50 anos, Palmieri propõe uma nova fase.

“A fase F é uma fase ecológica, que não diz respeito diretamente ao desenvolvimento da figueira, mas de seu papel no ciclo de desenvolvimento de outras dezenas de espécies de insetos que não são vespas-do-figo”, disse.

“Há uma série de organismos – insetos, ácaros, nematoides – que também conseguem parasitar os figos. A maior parte dos parasitas são outras vespas de grupos irmãos das vespas-do-figo. Elas conseguem inserir seus ovos dentro do fruto sem cumprir o papel biológico da polinização”, disse Palmieri.

As evidências da nova fase F começaram a surgir ao longo de anos de observação. “Durante o estudo da interação entre as figueiras e as vespas era comum encontrar larvas de outros bichos que não tinham participação no ciclo de desenvolvimento. Esses figos eram descartados da pesquisa e jogados fora. Em certos casos, havia larvas quase do tamanho do figo comendo tudo lá dentro. Foi quando decidimos investigar o que ocorria”, disse Palmieri à Agência Fapesp.

“Quando as larvas atingiam a fase adulta, começavam a sair dos figos podres uns bichos que ninguém conhecia. No artigo agora publicado, descrevo 129 insetos de cinco ordens e 24 famílias diferentes, que não são vespas-do-figo e que também interagem com a figueira realizando funções diferentes”, disse.

Palmieri identificou dez tipos de vespas (Hymenoptera), 39 tipos de moscas (Diptera), 46 tipos de besouros (Coleoptera), 17 de cigarras, percevejos, pulgões e cochonilhas (Hemiptera) e 18 de borboletas e mariposas (Lepidoptera).

Esses insetos podem colonizar os figos em diferentes fases do ciclo de desenvolvimento das figueiras e alguns grupos dependem dos figos caídos para completar seus ciclos de vida. De acordo com o seu papel na ecologia da figueira e seu potencial impacto na reprodução da figueira, Palmieri dividiu os insetos em duas categorias: os intrusos precoces do figo e a fauna dos figos caídos.

Todos os tipos de insetos identificados têm representantes em ambas as categorias. A exceção são as dez espécies de vespas de três famílias irmãs da família das vespas-do-figo. Todas são intrusas precoces que depositam dentro do figo ovos dos quais emergem larvas que competem diretamente com as larvas das vespas-do-figo por alimento e espaço dentro do figo, ou simplesmente se alimentam delas. Quando terminam o seu desenvolvimento e atingem a fase adulta, elas saem do figo.

No artigo, Palmieri descreve diversas formas de intrusão precoce dos figos. Uma delas é a das moscas do gênero Lissocephala, que põem ovos no ostíolo no momento de entrada da vespa mãe. As larvas de mosca vão migrar para dentro do figo e se alimentar de fungos e bactérias introduzidos pela vespa. Essas moscas terminam seu desenvolvimento dentro do figo e voam pelo buraco cavado pelas vespas machos.

Fauna extremamente diversificada de insetos associados aos figos também deve ser fator relacionado ao sucesso das cerca de 750 espécies de figueiras – Foto: Divulgação

As borboletas e mariposas são o grupo mais agressivo de insetos em termos de danos causados ao figo. Elas depositam ovos na casca. Na fase C, suas larvas perfuram a parede do figo e se alimentam indiscriminadamente da polpa, das vespas e das sementes. As larvas de borboletas e mariposas destroem o figo e emergem para poder pupar em casulos nos galhos da figueira.

Palmieri explica que, no caso da fauna dos figos caídos, essa categoria engloba uma variedade de organismos que se alimentam de restos carnudos ou de sementes de figos maduros não consumidos pelos vertebrados frugíferos. Eles aproveitam a janela de oportunidade criada pelos figos que caem da árvore na fase F.

A fauna dos figos caídos, da qual fazem parte algumas formigas, borboletas e percevejos, é principalmente composta de besouros que se alimentam dos restos da fruta. Há diversas formas de os besouros se aproveitarem do desenvolvimento dos figos. Alguns colonizam os figos ainda na árvore, durante o início da fase C. Suas larvas se desenvolvem dentro dos figos e lá permanecem quando os frutos maduros caem ao chão. Só então as larvas migram para o solo, onde cavam um buraco e pupam no interior de casulos.

“Estes exemplos fornecem tão somente o vislumbre de uma complexidade muito maior de interações. Além das implicações evolutivas do mutualismo da polinização, um fator adicional relacionado ao sucesso das cerca de 750 espécies de figueiras é provavelmente a fauna extremamente diversificada de insetos associados aos figos – tais como as espécies de vespas que não aquelas polinizadoras. A pressão dessas vespas parasitas deve ter servido de importante fator impulsionador da diversificação das diversas espécies de figueiras. E continua a sê-lo”, disse Palmieri.

O artigo The role of non-fig-wasp insects on fig tree biology, with a proposal of the F phase (Fallen figs), de Luciano Palmieri e Rodrigo Augusto Santinelo Pereira, foi publicado na Elsevier ScienceDirect.

Diferenças no ovipositor

As vespas-do-figo compreendem cerca de 650 espécies descritas, pertencentes a diversas famílias. Mas esse número representa menos da metade do número estimado de espécies, incluindo as vespas polinizadoras e as parasitas, não polinizadoras.

“São vespas oportunistas, que põem ovos pelo lado de fora do figo. Fazem uso de uma estrutura chamada ovipositor para atravessar a casca do figo e inserir o ovo dentro de uma flor ou galha”, disse Larissa Galante Elias, pesquisadora no Laboratório de Interação Inseto-Planta da FFCLRP.

Em outro artigo, publicado na edição especial da Acta Oecologica, Larissa analisa diferenças morfológicas no ovipositor de diversas espécies de vespas polinizadoras e não polinizadoras. O estudo, orientado pelo professor Santinelo Pereira, tem apoio da Fapesp.

“Ao longo de milhões de anos de evolução, o ovipositor foi se modificando para ganhar outras funções. Minha questão é entender como as vespas conseguem fazer coisas tão complexas e diferenciadas com o ovipositor, como botar ovos pelo lado de fora do figo e acertar exatamente o interior da flor, ou pôr o ovo dentro de galhas, ou ainda na casca do figo. Nas vespas atuais, vemos o ovipositor realizando todas essas funções”, disse.

Larissa é a primeira autora de um artigo Ovipositor morphology correlates with life history evolution in agaonid fig wasps no qual, ao lado de outros pesquisadores do Brasil, França e China, analisa a variação morfológica no ovipositor em 24 espécies de vespas-do-figo pertencentes a nove gêneros diferentes.

“O ovipositor é uma estrutura comum a todas as espécies de vespas, porém ligeiramente diferente em cada uma delas. É muito fino e muito comprido e pode ser até três vezes maior do que o corpo da vespa”, disse Larissa.

As vespas-do-figo polinizadoras põem ovos quando as flores são jovens. As flores da figueira são todas aquelas centenas de filamentos no interior do figo, que têm na base uma estrutura redonda. Cada flor que contém uma larva irá se transformar em uma galha.

As vespas parasitas botam ovos ao mesmo tempo que a polinizadora ou então um pouco mais tarde, quando as larvas estão em pleno desenvolvimento dentro das galhas. “Elas podem parasitar centenas de galhas, mas vão depositar um único ovo em cada galha. Suas larvas irão se alimentar das outras larvas preexistentes”, explicou Larissa.

Em seu trabalho, a pesquisadora realizou uma análise de reconstrução de estados ancestrais. A análise permite a interpretação da evolução de diversos caracteres morfológicos, ecológicos e comportamentais na evolução de um dado grupo de organismos.

“O ovipositor tem na sua extremidade estruturas que se parecem com dentes. Percebi que a morfologia desses dentes variava muito. Decidi investigar se as estruturas variam entre as diversas vespas, dependendo da fase do ciclo de desenvolvimento do figo na qual elas botam ovos, por exemplo se quando o figo é jovem ou quando as galhas estão formadas”, disse.

Foram feitas amostras de 24 espécies pertencentes a todos os principais clados (agrupamento que inclui um ancestral comum) de agaonídeos, incluindo representantes de todos os gêneros descritos de vespas não polinizadoras da família. Havia espécies do Brasil, Austrália, China, Laos, Senegal, Indonésia, Camarões, Índia e das Ilhas Salomão, algumas coletadas em campo, outras obtidas da coleção de Jean Yves Rasplus, do Centre de Biologie pour la Gestion des Populations do Institut National de la Recherche Agronomique (Inra), na França.

Em estereomicroscópio, Larissa realizou uma série de medidas do corpo e do ovipositor de dez a 20 indivíduos de cada espécie. Foram analisados caracteres relacionados aos dentes dos ovipositores quanto ao seu potencial papel na perfuração e ancoragem do ovipositor, permitindo a sua movimentação pelo substrato do figo.

“Percebi que a distância entre os dentes do ovipositor está relacionada com o que a vespa está fazendo. Os dentes podem ser mais espaçados ou mais próximos uns dos outros”, disse.

Os insetos estudados por Larissa pertencem a grupos ecológicos diferentes. As vespas que inserem ovos perfurando a casca do figo com o ovipositor quando os figos estão jovens – e que vão depositar ovos nas flores lá dentro – são chamadas galhadoras, pois a deposição dos ovos estimulará o desenvolvimento da galha. “Descobrimos que, no caso das vespas galhadoras, os dentes do ovipositor estão mais juntos”, disse.

Em outro grupo estão as vespas que, desde a casca do figo, utilizam o ovipositor para inserir ovos dentro das galhas. São as parasitoides, que parasitam a galha. “No caso, os dentes têm formato irregular e são mais espaçados”, disse.

“O resultado da análise de reconstrução de estados ancestrais sugere que a vespa ancestral das vespas agaonídeas tinha o ovipositor adaptado para botar o ovo nas flores jovens”, disse Larissa. Ou seja, o ovipositor foi sendo adaptado para inserir ovos na fase da galha mais tarde, ao longo de milhões de anos, sendo uma ferramenta na diversificação do grupo.

“Ter esse novo método de identificação do tipo de vespa-do-figo por meio da análise do ovipositor é interessante, pois não há mais a necessidade de acompanhar todo o ciclo de desenvolvimento do figo para conseguir identificar qual vespa está fazendo o que dentro daquele contexto de interações”, disse Larissa.

O artigo Ovipositor morphology correlates with life history evolution in agaonid fig wasps, de Larissa Galante Elias, Finn Kjellberg, Fernando Henrique Antoniolli Farache, Eduardo A.B. Almeida, Jean-Yves Rasplus, Astrid Cruaud, Yan-Qiong Peng, Da-Rong Yang e Rodrigo Augusto Santinelo Pereira, está publicado na Science Direct .

A edição especial com os quatro artigos de pesquisadores brasileiros está disponível em Science Direct Acta-oecologica.

Peter Moon / Agência Fapesp

Link:
https://jornal.usp.br/ciencias/ciencias-biologicas/relacao-de-mutualismo-entre-figueiras-e-vespas-tem-nova-fase-revelada/

Plants evolve away from obsolete defenses when attacked by immune herbivores, study shows

Date: February 26, 2018 Source: Drexel University Summary: A new study shows that plants can evolve out of their obsolete defense mechanisms when facing an immune enemy, an illustration of the 'defense de-escalation' evolution theory.

Do you know what caused soldiers to stop wearing chainmail and steel plate armor? Evolution.

Really, guns made armies drop steel gauntlets and breastplates. Bullets that could punch through armor quickly made it obsolete. So, armies evolved away from armor because it wasn't working any longer and there was no point in spending the resources on it. "Adapt or die," as the saying goes.

Now, new research out of the Academy of Natural Sciences of Drexel University shows that plants similarly adapt away from obsolete defenses.

The study, published in New Phytologist and led by Tatyana Livshultz, PhD, assistant curator of Botany at the Academy and an assistant professor in the College of Arts and Sciences, found genetic evidence that multiple lineages of plants, whose ancestors produced a chemical that may deter herbivores, evolved to stop producing it, potentially as a response to a prime foe's immunity.

Livshultz and her team traced the evolution of a gene that is involved in the production of a class of chemicals that are highly toxic to humans and other mammals, called pyrrolizidine alkaloids, in Apocynaceae, a flowering plant family commonly known as the dogbanes and milkweeds. By tracing the gene back, they were able to find out when production of the chemicals first evolved and how many times it was discontinued.

After identifying a single origin of the gene (and, by inference, the chemicals) in the most recent common ancestor of more than 75 percent of current Apocynaceae species, the researchers found evidence that the gene became nonfunctional (and the chemicals "lost" to evolution) at least four different times among that plant's descendants.

Looking for a correlation between the gene's distribution in the plants and interactions with animals unfazed by the defense alkaloids, Livshultz and her team found a significant connection with Danainae (milkweed and clearwing) butterflies.

Almost every species of Apocynaceae eaten by larvae of Danainae is descended from that alkaloid-producing ancestor. Knowing that most species of this lineage of butterflies actually seek out pyrrolizidine alkaloids, it appears that some species in this branch of Apocynaceae may have stopped producing the alkaloids because they were actually attracting milkweed butterflies, not repelling them.

"Pyrrolizidine alkaloids are likely an ineffective defense against Danainae. Furthermore, they are actually beneficial to them since they take in these chemicals for their own defense against their predators," Livshultz explained.

These findings support the "defense de-escalation" hypothesis, which posits that organisms will evolve to stop using precious resources on defense mechanisms if they're not working anymore.

One benefit of defense de-escalation is potentially diverting resources to defenses that do work.

"Apocynaceae species of this lineage produce a number of different classes of defensive chemicals, including cardenolides and other types of alkaloids," Livshultz explained. "It has been shown that cardenolides are at least partially effective defenses against adapted herbivores such as the monarch butterfly, the most familiar species of Danainae to Americans."

Why do any Apocynaceae species still produce pyrrolizidine alkaloids? -- "perhaps because they suffer more from other insects that are deterred by these chemicals," Livshultz offered.

Livshultz and her colleagues will further test the hypothesis by reconstructing a very detailed history of the pattern of retention and loss of pyrrolizidine alkaloids in this lineage and ask if exploitation by Danainae is a good predictor of loss.

A better understanding of the dynamics of defense de-escalation is important to understanding co-evolution, the theory that associated species driving each other's adaptations.

"Co-evolution explains how interactions between species can drive the origin of novelty and diversity," Livshultz said.

Additionally, implications from these theories extend beyond plants to humans.

"Understanding the evolution of plant defenses is of practical importance to people, whether we focus on agriculture -- herbivorous insects can cause 15 percent reductions in crop yields; medicine -- plant secondary metabolites (pyrrolizidine alkaloids are one variety) are an important source of medicinal compounds; or environmental protection -- such as developing control strategies for invasive plants," Livshultz said.

Story Source:

Materials provided by Drexel University. Original written by Frank Otto. Note: Content may be edited for style and length.

Journal Reference:
Tatyana Livshultz, Elisabeth Kaltenegger, Shannon C. K. Straub, Kevin Weitemier, Elliot Hirsch, Khrystyna Koval, Lumi Mema, Aaron Liston. Evolution of pyrrolizidine alkaloid biosynthesis in Apocynaceae: revisiting the defence de-escalation hypothesis. New Phytologist, 2018; DOI: 10.1111/nph.15061

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Drexel University. "Plants evolve away from obsolete defenses when attacked by immune herbivores, study shows." ScienceDaily. ScienceDaily, 26 February 2018. <www.sciencedaily.com/releases/2018/02/180226085815.htm>.

More than bugs: Spiders also like an occasional vegetarian meal

Date: March 14, 2016

Source: University of Basel

Summary:

Spiders are known to be the classic example of insectivorous predators. Zoologists have now been able to show that their diet is more diverse than expected. Their findings show that spiders like to spice up their menu with the occasional vegetarian meal.

Jumping spider (stock image).

Credit: © zleng8229 / Fotolia

Spiders are known to be the classic example of insectivorous predators. Zoologists from the University of Basel, the US and UK have now been able to show that their diet is more diverse than expected. Their findings show that spiders like to spice up their menu with the occasional vegetarian meal. The Journal of Arachnology has published the results.

Although traditionally viewed as a predator of insects, researchers have become increasingly aware that spiders are not exclusively insectivorous. Some spiders have been shown to enrich their diets by occasionally feasting on fish, frogs or even bats. A new study by Zoologists from the University of Basel, Brandeis University (US) and Cardiff University (UK) now shows evidence of spiders eating plant food as well.

Plants as diet supplement

The researchers gathered and documented numerous examples from literature of spiders eating plant food. According to their systematic review, spiders from ten families have been reported feeding on a wide variety of different plant types such as trees, shrubs, weeds, grasses, ferns or orchids. They also show a diverse taste when it comes to the type of plant food: nectar, plant sap, honeydew, leaf tissue, pollen and seeds are all on the menu.

The most prominent group of spiders engaged in plant-eating are Salticidae – a diurnal spider family with characteristically large anterior median eyes. Salticidae were attributed with up to 60 percent of all plant-eating incidents documented in this study. As plant-dwelling, highly mobile foragers with excellent capability to detect suitable plant food, these spiders seems to be predestined to include some plant food in their diets.

Global feeding behavior

Spiders feeding on plants is global in its extent, as such behavior has been reported from all continents except Antarctica. However, it is documented more frequently from warmer areas. The researchers suggest that this might be due to the fact that a larger number of the reports relate to nectar consumption which has its core distribution in warmer areas where plants secreting large amounts of nectar are widespread.

“The ability of spiders to derive nutrients from plants is broadening the food base of these animals; this might be a survival mechanism helping spiders to stay alive during periods when insects are scarce”, says lead author Martin Nyffeler from the University of Basel in Switzerland. “In addition, diversifying their diet with plant is advantageous from a nutritional point of view, since diet mixing is optimizing nutrient intake.” However, the extent to which the different categories of plant food contribute to the spiders’ diet is still largely unexplored.

Story Source:

Materials provided by University of Basel. Note: Content may be edited for style and length.

Journal Reference:

Martin Nyffeler, Eric J. Olson, William O.C. Symondson. Plant-eating by spiders. Journal of Arachnology, 2016; 44 (1): 15 DOI: 10.1636/P15-45.1

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University of Basel. "More than bugs: Spiders also like an occasional vegetarian meal." ScienceDaily. ScienceDaily, 14 March 2016. <www.sciencedaily.com/releases/2016/03/160314091121.htm>.

Whitefly confused by cacophony of smells

Date: April 28, 2014

Source: Newcastle University

Summary:

Bombarding pests with smells from many different plants temporarily confuses them and hinders their ability to feed, new research has shown. Exposing the whitefly to a heady aroma of cucumber, courgette, watercress, watermelon, cabbage and bean, the team found the insects became temporarily disorientated. Weaving their way between the plant cells to reach the sap is technically challenging and the team found the whiteflies failed to feed while they were being bombarded with the different plant chemicals.

Bombarding pests with smells from many different plants temporarily confuses them and hinders their ability to feed, new research has shown.

Biologists at Newcastle University, UK, have been exploring the potential of harmless plant volatiles as an alternative to pesticides in greenhouses.

Testing a phenomenon known as the 'confusion effect' -- whereby animals and humans become inefficient at a task when they are bombarded with lots of distracting information -- the team pumped a mixture of plant smells into a greenhouse growing tomato plants.

Exposing the whitefly to a heady aroma of cucumber, courgette, watercress, watermelon, cabbage and bean, the team found the insects became temporarily disorientated.

Like other insect pests, whitefly feed by pushing their long mouthpiece -- or stylets -- into the leaf until it reaches the plant's main source of nutrients travelling through the phloem. Weaving their way between the plant cells to reach the sap is technically challenging and the team found the whiteflies failed to feed while they were being bombarded with the different plant chemicals.

Publishing their findings this week in the academic journal Agronomy of Sustainable Development, research leads Dr Colin Tosh and Dr Barry Brogan said this method of control could be an important step towards a more sustainable method of pest control.

"It's like trying to concentrate on work while the TV's on and the radio's blaring out and someone's talking to you," explains Dr Tosh, based in Newcastle University's School of Biology. "You can't do it -- or at least not properly or efficiently -- and it's the same for the whitefly.

"Whiteflies use their sense of smell to locate tomato plants. By bombarding its senses with a range of different smells we create 'sensory confusion' and the result is that the insect becomes disorientated and is unable to feed.

"Because the effect is temporary -- we saw it last no more than 15 hours -- it's unlikely this method alone could be used to control crop pests. But this is an easy and safe way of buying the plants time until their own chemical defense mechanisms kick in. Used in conjunction with other methods, sensory confusion opens up a whole new area in sustainable pest control."

Trialeurodes vaporariorum -- or whitefly -- is a major worldwide pest of greenhouse crops and is traditionally controlled using chemical pesticides or biological methods such as parasites.

Previous studies have shown that whitefly become 'restless' when a number of plant species are mixed together rather than being exposed to a single crop. The aim of this latest research, funded by the Natural Environment Research Council (NERC), was to artificially create this mixed environment for a single crop greenhouse.

Measuring the time it took from the insect settling on a plant to accessing the plant sap, the team showed that hardly any of the whiteflies exposed to a range of smells started feeding from the phloem within 15 hours from the time of exposure. By comparison, the majority of whiteflies exposed to just the single smell released by the tomato plants started feeding within this time.

Dr Brogan, also based in the School of Biology, adds: "Plants talk to each other when they are under attack -- producing chemicals which warn other plants close by of the threat. At the same time, they produce a chemical which is unpleasant to the predator.

"But this response doesn't happen immediately, so if we can confuse the insects long enough to give the plants time to defend themselves this may go someway to reducing crop losses."

The team have now started the next phase of the study to investigate ways of helping plants to talk to each other and better switch on their defenses.

Story Source:

Materials provided by Newcastle University. Note: Content may be edited for style and length.

Journal Reference:

Colin R. Tosh, Barry Brogan. Control of tomato whiteflies using the confusion effect of plant odours. Agronomy for Sustainable Development, 2014; DOI: 10.1007/s13593-014-0219-4

Cite This Page:

Newcastle University. "Whitefly confused by cacophony of smells." ScienceDaily. ScienceDaily, 28 April 2014. <www.sciencedaily.com/releases/2014/04/140428074646.htm>.

'Neighbor plants' determine insects' feeding choices

Date: February 14, 2014

Source: Netherlands Institute of Ecology (NIOO-KNAW)

Summary:

Insects are choosier than you might think: whether or not they end up feeding on a particular plant depends on much more than just the species to which that plant belongs. The quality of the individual plant is an important factor as well. As is the variety of other plants growing around it. But what, ultimately, makes an insect choose one plant over another?

In her PhD thesis, Olga Kostenko uses ragwort as an example to show that the ‘neighborhood’ in which a plant grows is more important for insects in the end than how the plant tastes.

Credit: Netherlands Institute of Ecology

Insects are choosier than you might think: whether or not they end up feeding on a particular plant depends on much more than just the species to which that plant belongs. The quality of the individual plant is an important factor as well. As is the variety of other plants growing around it. But what, ultimately, makes an insect choose one plant over another?

It's a question ecologists have struggled with for decades, and the answer could have a major impact on attempts to use insects for controlling crops or attacking outbreak species such as ragwort. Ragwort (Jacobaea vulgaris) is native to the Netherlands but its abundance in areas such as ex-arable fields can make it a pest, as it is toxic to horses and farmers can't use fields where it grows for hay.

In her PhD thesis, Olga Kostenko uses ragwort as an example to show that the 'neighborhood' in which a plant grows is more important for insects in the end than how the plant tastes. If, for instance, ragwort plants grow in a plant community with many tall neighbors, insects will not even notice them. Consequently, the effectiveness of using insects to control such plants is limited.

Field experiments

But before she could weigh the importance of these factors, Kostenko first had to do some pioneering research into plant quality in particular. Most knowledge about the role of plant quality so far had been based on controlled laboratory experiments. Whether it would still be as important a factor under natural conditions was unknown.

Kostenko took up the challenge, planting no fewer than 1750 plants on ex-arable fields at Mossel (Ede, the Netherlands), with remarkable results. Not only did she find that plant quality wasn't the most important factor, she also discovered that the way the plants tasted to insects was actually affected by the neighborhood in which they grew.

And not just the present neighborhood: even plants and insects that inhabited the same spot in the past had an effect on the chemical composition of the next generation of plants. These changes in turn affected the number and the performance of insects feeding on an individual plant.

So for ragwort, having good -- or bad -- neighbors is literally a matter of life and death.

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Materials provided by Netherlands Institute of Ecology (NIOO-KNAW). Note: Content may be edited for style and length.

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Netherlands Institute of Ecology (NIOO-KNAW). "'Neighbor plants' determine insects' feeding choices." ScienceDaily. ScienceDaily, 14 February 2014. <www.sciencedaily.com/releases/2014/02/140214101557.htm>.

Caterpillars that eat multiple plant species are more susceptible to hungry birds

Date: June 16, 2014

Source: University of California - Irvine

Summary:

Biologists have learned that caterpillars that feed on one or two plant species are better able to hide from predatory birds than caterpillars that consume a wide variety of plants.

A tiger swallowtail (Papilio glaucus) caterpillar feeds on black cherry (Prunus serotina), which was the only plant consumed by this species at the research field site.

Credit: Michael Singer / Wesleyan University

For caterpillars, having a well-rounded diet can be fraught with peril.

UC Irvine and Wesleyan University biologists have learned that caterpillars that feed on one or two plant species are better able to hide from predatory birds than caterpillars that consume a wide variety of plants.

This is probably because the color patterns and hiding behaviors of the caterpillar "specialists" have evolved to allow them to blend into the background flora more effectively than caterpillars that eat many different plant species. Moving among these diverse plant types, the nonspecialists are not as camouflaged, making them easier for hungry birds to spot.

"It's a classic example of risk vs. reward," said Kailen Mooney, associate professor of ecology & evolutionary biology at UC Irvine. "Evolutionarily speaking, a caterpillar must choose between having a broad array of plants to feed upon but facing increased risk of being nabbed by a bird" and having a very limited menu but being less exposed to predators.

Mooney and Michael Singer, associate professor of biology at Wesleyan, led the study, which appears in the early online edition of Proceedings of the National Academy of Sciences this week.

Furthermore, the researchers found that all of this matters a lot to the plants. A species consumed by caterpillars more vulnerable to birds (those with varied diets) benefits from birds removing those caterpillars. In contrast, a plant species fed upon by caterpillars better able to hide from birds (those with highly restricted diets) doesn't benefit as much from birds and must instead defend itself.

Mooney noted that this insight into the secret lives of caterpillars reveals not only the processes driving the evolution of insect diets but also the broad significance of caterpillar feeding for associated plants and birds.

Story Source:

Materials provided by University of California - Irvine. Note: Content may be edited for style and length.

Journal Reference:

M. S. Singer, I. H. Lichter-Marck, T. E. Farkas, E. Aaron, K. D. Whitney, K. A. Mooney. Herbivore diet breadth mediates the cascading effects of carnivores in food webs. Proceedings of the National Academy of Sciences, 2014; DOI: 10.1073/pnas.1401949111

Cite This Page:

University of California - Irvine. "Caterpillars that eat multiple plant species are more susceptible to hungry birds." ScienceDaily. ScienceDaily, 16 June 2014. <www.sciencedaily.com/releases/2014/06/140616151500.htm>.

Caterpillars attracted to plant SOS

Date: July 1, 2013

Source: Frontiers

Summary:

Plants that emit an airborne distress signal in response to herbivory may actually attract more enemies, according to a new study.

This image shows the detail of the four-arm olfactometer setup for S. littoralis larval behavior.

Credit: Drawing by Thomas Degen (www.thomas-degen.ch)

Plants that emit an airborne distress signal in response to herbivory may actually attract more enemies, according to a new study published in the open-access journal Frontiers in Plant Science .

A team of researchers from Switzerland found that the odor released by maize plants under attack by insects attract not only parasitic wasps, which prey on herbivorous insects, but also caterpillars of the Egyptian cotton leafworm moth Spodoptera littoralis, a species that feeds on maize leaves.

When damaged, many plants release hydrocarbons called volatile organic compounds, similar to the compounds that cause the characteristic smell of freshly cut grass. These volatile organic compounds are known to be attractive to parasitoid wasps that lay their eggs inside other insects, killing them. Plants appear to use this strategy to fight back against herbivorous insects by calling for their enemies' enemies. In contrast, herbivorous insects tend to avoid the herbivore-induced volatile organic compounds.

"Adult moths and butterflies avoid food plants that are under attack by conspecifics. This seems adaptive, because it reduces both competition and the risk of predation by parasitoids. But we found that S. littoralis caterpillars are actually attracted to the odor of damaged maize plants, even when this odor is mimicked in the laboratory with a mix of synthetic compounds," said Prof. Ted Turlings, an author of the study and head of the Laboratory for Fundamental and Applied Research in Chemical Ecology Institute of Biology at the University of Neuchâtel, Switzerland.

To determine what kind of odors the caterpillars preferred, the researchers let the caterpillars chose among several odors by placing them in an olfactometer, a device consisting of four tubes connected to a central chamber, with each tube introducing an airflow carrying a different odor. The caterpillars were more than twice as likely to crawl towards the odor from maize plants under attack by conspecifics than towards undamaged plants, especially if the damage was recent and the caterpillars had already fed on maize.

So what might be the advantage to the caterpillars of moving towards plants that are already infested? "When S. littoraliscaterpillars drop from a plant they are highly vulnerable to predators and pathogens in the soil, as well as to starvation. The advantage seems to be that fallen caterpillars can quickly rediscover the plant on which they fed. The caterpillars feed less and move more when exposed to high concentrations of the volatiles. By moving away from freshly damaged sites, they can minimize risk of predation and avoid competition," explained Prof. Turling.

Turlings and colleagues propose that hungry S. littoralis caterpillars do the best of a bad job by moving towards volatile organic compounds released by damaged maize plants. On these plants the competition may be more intense, but at least the caterpillars are assured of a suitable plant. Adult moths, on the other hand, are much more mobile and take little risk exploring the environment to discover the best food source -- so they avoid maize that is already under attack.

Story Source:

Materials provided by Frontiers. Note: Content may be edited for style and length.

Journal Reference:

Georg E. von Mérey, Nathalie Veyrat, Marco D'Alessandro, Ted C. J. Turlings. Herbivore-induced maize leaf volatiles affect attraction and feeding behavior of Spodoptera littoralis caterpillars. Frontiers in Plant Science, 2013; 4 DOI: 10.3389/fpls.2013.00209

Cite This Page:

Frontiers. "Caterpillars attracted to plant SOS." ScienceDaily. ScienceDaily, 1 July 2013. <www.sciencedaily.com/releases/2013/07/130701135820.htm>.

Harm and response: Plants recognize and respond to different insects

Date: February 13, 2015

Source: University of Missouri-Columbia

Summary:

In one of the broadest studies of its kind, scientists recently looked at all plant genes and their response to the enemy. Their results showed that the model Arabidopsis plant recognizes and responds differently to four insect species. The insects cause changes on a transcriptional level, triggering proteins that switch on and off plant genes to help defend against more attacks.

University of Missouri Bond Life Sciences Center's Jack Schultz and Heidi Appel hold model Arabidopsis plants used in many of their experiments.

Credit: Roger Meissen/Bond LSC

We often think of damage on a surface level.

But for plants, much of the important response to an insect bite takes place out of sight. Over minutes and hours, particular plant genes are turned on and off to fight back, translating into changes in its defenses.

In one of the broadest studies of its kind, scientists at the University of Missouri Bond Life Sciences Center recently looked at all plant genes and their response to the enemy.

"There are 28,000 genes in the plant, and we detected 2,778 genes responding, depending on the type of insect," said Jack Schultz, Bond LSC director and study co-author. "Imagine you only look at a few of these genes, you get a very limited picture and possibly one that doesn't represent what's going on at all. This is by far the most comprehensive study of its type, allowing scientists to draw conclusions and get it right."

Their results showed that the model Arabidopsis plant recognizes and responds differently to four insect species. The insects cause changes on a transcriptional level, triggering proteins that switch on and off plant genes to help defend against more attacks.

The difference in the insect

"It was no surprise that the plant responded differently to having its leaves chewed by a caterpillar or pierced by an aphid's needle-like mouthparts," said Heidi Appel, Bond LSC Investigator and lead author of the study. "But we were amazed that the plant responded so differently to insects that feed in the same way."

Plants fed on by caterpillars -- cabbage butterfly and beet armyworms -- shared less than a quarter of their changes in gene expression. Likewise, plants fed on by the two species of aphids shared less than 10 percent of their changes in gene expression.

The plant responses to caterpillars were also very different than the plant response to mechanical wounding, sharing only about 10 percent of their gene expression changes. The overlap in plant gene responses between caterpillar and aphid treatments was also only 10 percent.

"The important thing is plants can tell the insects apart and respond in significantly different ways," Schultz said. "And that's more than most people give plants credit for."

A sister study explored this phenomena further, led by former MU doctoral student Erin Rehrig.

It showed feeding of both caterpillars increased jasmonate and ethylene -- well-known plant hormones that mediate defense responses. However, plants responded quicker and more strongly when fed on by the beet armyworm than by the cabbage butterfly caterpillar in most cases, indicating again that the plant can tell the two caterpillars apart.

The result is that the plant turns defense genes on earlier for beet armyworm.

In ecological terms, a quick defense response means the caterpillar won't hang around very long and will move on to a different meal source.

More questions

A study this large has potential to open up a world of questions begging for answers.

"Among the genes changed when insects bite are ones that regulate processes like root growth, water use and other ecologically significant process that plants carefully monitor and control," Schultz said. "Questions about the cost to the plant if the insect continues to eat would be an interesting follow-up study for doctoral students to explore these deeper genetic interactions."

Story Source:

Materials provided by University of Missouri-Columbia. Original written by Roger Meissen. Note: Content may be edited for style and length.

Journal Reference:

Heidi M. Appel, Howard Fescemyer, Juergen Ehlting, David Weston, Erin Rehrig, Trupti Joshi, Dong Xu, Joerg Bohlmann, Jack Schultz. Transcriptional responses of Arabidopsis thaliana to chewing and sucking insect herbivores. Frontiers in Plant Science, 2014; 5 DOI:10.3389/fpls.2014.00565

Cite This Page:

University of Missouri-Columbia. "Harm and response: Plants recognize and respond to different insects." ScienceDaily. ScienceDaily, 13 February 2015. <www.sciencedaily.com/releases/2015/02/150213104721.htm>.