https://news.missouri.edu/2020/bee-thankful-for-the-evolution-of-pollen/

‘Bee' thankful for the evolution of pollen

Missouri U. researchers discover wildflower's spiny pollen

adapts to help plants reproduce

Over 80% of the world's flowering plants must reproduce in order to produce new flowers, according to the U.S. Forest Service. This process involves the transfer of pollen between plants by wind, water or insects called pollinators -- including bumblebees.

In a new study, researchers at the University of Missouri discovered spiny pollen -- from a native wild dandelion species in the southern Rocky Mountains -- has evolved to attach to traveling bumblebees. Using a highly detailed electron scanning microscope, the research team could observe the microscopic surface of the spiny pollen, which otherwise looks like yellow dust to the naked eye.

"The spiny pollen actually acts like Velcro," Lynn said. "So, when bees are harvesting pollen for food, this pollen is sticking to their hair. It's a great example of mutualism where the plant needs the pollinator to reproduce and the pollinator needs the plant for its food."

The researchers plan to study how a bumblebee's hairs contribute to this process.

For more on how clever plants are, check out Michael Pollan's Botany of Desire.

The Buzz about Hedgerows

Hedgerows are an approved practice under California Department of Agriculture's Healthy Soils Grant Program. That means, growers are eligible to receive grant funding for planting hedgerows. But what exactly are the benefits of hedgerows and why are they worth planting? As a perennial planting it can have immediate impacts on the soil, but what else? The answer lies large in the pollinators and beneficial insects they attract.

The most basic definition of a hedgerow is dense vegetation planted in a linear design. Perennial grasses, shrubs, and even short trees are all candidates for hedgerow plantings, provided they meet the conditions of the local climate and soil. Growers plant hedgerows to achieve one or more of the following desired outcomes:

-          To increase habitat for pollinator and beneficial insect populations

-          To create a living barrier or fence

-          To reduce chemical drift or odor movement

-          To intercept airborne particulate matter

-          To act as a low windbreak or reduce dust

-          To increase carbon storage in biomass and soils

-          To provide food, shelter, and shade for aquatic organisms in nearby aquatic habitats

All of these benefits make the case for planting hedgerows on any agricultural operation. In Ventura County, avocado growers stand to see a compelling case for hedgerow plantings with particular attention to pollination services.

Agapostemon texanus, a native pollinator of avocados. Photo by Rollin Coville.

There are many different pollinators who visit avocado flowers, from native bees to flies to honey bees. Some come in the daytime, others visit at night. In the likelihood that honey bees and other pollinators will continue to decline, it is imperative to study the importance of native pollinators on key crops and identify ways to increase habitat for resident populations (NRC 2007; Nordhaus 2011; PHTF 2015; Koh et al. 2016; Sánchez-Bayo and Wyckhuys 2019; DiBartolomeis et al. 2019; Garibaldi et al. 2013). This information not only helps the pollinator populations thrive, but helps avocado growers acquire free increased pollination services for fruitful trees. Several researchers have published accounts of increased pollinator diversity and numbers in hedgerow and field edge planting studies across various agricultural systems (Heller et al. 2019; Long and Anderson 2010; Long et al. 2017; Williams et al. 2015).

In Ventura County, we are seeing some fascinating and relevant research around the impact of hedgerows on pollinators in avocado orchards. A collaborative research project involving Dr. Ben Faber, Avocado Advisor for UC Cooperative Extension Ventura County, and Dr. Gordon Frankie, professor and research entomologist at UC Berkeley and lead investigator of the UC Berkeley Urban Bee Lab, seeks to understand long-term impacts of hedgerows on pollinators of avocado trees. The project, which began in 2014 with three participating avocado ranches, has indicated increased pollinator activity, increased native bee populations, and increased diversity of species with the presence of hedgerow plantings (Frankie, Faber et al. 2020). The results indicate the importance of diversity of pollinator species, not just the honeybee, to avocados. In continuing this research, the team seeks to address the unanswered questions of which pollinators are the most effective at pollinating avocados and which are the most effective at influencing fruit set. A particularly exciting and novel aspect of this project is looking at whether or not there are nocturnal pollinators visiting California avocados. Nocturnal pollinators have been well documented in New Zealand (Pattemore et al, 2018), but none have been yet recorded in California avocados.

A blooming pollinator garden and research site at Jim Lloyd Butler's avocado ranch in Ventura County. Photo by Gordon Frankie.

Maintaining hedgerows is critical to providing additional habitat for an abundance of pollinators. Creating and maintaining that hedgerow and for which pollinators can be a daunting task to embark on. Luckily for avocado growers, Dr. Frankie and Dr. Faber's team are working with Southern California growers to develop a pollinator garden manual. The manual will provide clear pictures of key pollinators and key plant species that pollinators are drawn to. Detailed imagery, descriptions, and maintenance tips will help make the decision making around planting a hedgerow much easier.     

Speaking of selections, there are key plants that are drought-tolerant, easy to maintain, and well-suited for Ventura County's climate. See the table below for some ideas.

Table 1. Main Native Bee Plants Installed in Avocado Orchards 2014-2019

We seek to increase biodiversity, build soil health, and reduce energy use in our agricultural systems to improve our resiliency to climate change impacts, pests, and disease. To keep farming in our families and in our futures. Planting hedgerows is good for the pollinators, which is good for the bottom line and long-term success of the operation.

If you are an avocado grower interested in learning more about the pollinator research project, please contact Dr. Gordon Frankie at the UC Berkeley Urban Bee Lab gwfrankie@berkeley.edu.

Interested in planting hedgerows on your property? You may be able to qualify for a grant through CDFA's Healthy Soils Grant Program to plant hedgerows. Please contact Jamie Whiteford with the Ventura County Resource Conservation District at jamiewhiteford.vcrcd@gmail.comfor more information on how to apply.  For those in other areas, Technical Assistance providers are able to discuss the values of hedgerows and funding opportunities for installing them in other agricultural situations: http://ciwr.ucanr.edu/Programs/ClimateSmartAg/TechnicalAssistanceProviders/

Bombus vosnesenskii photo by Rollin Coville

References Cited

DiBartolomeis, M., S. Kegley, P. Mineau, R. Radford, and K. Klein. 2019. An assessment of acute insecticide toxicity loading (AITL) of chemical pesticides used on agricultural land in the United States. PLoS ONE 14(8): e0220029. https://doi.org/10.1371/journal.pone.0220029.

Frankie, G., B. Faber, J. Pawelek, R. Thorp, R. Coville, C. Jadallah, E. Takele, S. I. Rios, T. Bean. 2020. Native Pollinators of California Avocado as Affected by Introduced Pollinator Gardens. International Society of Horticultural Sciences Congress. Acta Horticulturae.

Garibaldi, L.A., I. Steffan-Dewenter, R. Winfree, and 47 other authors. 2013. Wild pollinators enhance fruit set of crops regardless of honey bee abundance. Science 339:1608-1611.

Heller, S., N. K. Joshi, T. Leslie, E. G. Rajotte and D. J. Biddinger. 2019. Diversified Floral Resource Plantings Support Bee Communities after Apple Bloom in Commercial Orchards. Scientific Reports 9 Article number: 17232.

Koh, I., Lonsdorf, E. V., Williams, N. M., Brittain, C., Isaacs, R., Gibbs, J., Ricketts, T. H. 2016. Modeling the status, trends, and impacts of wild bee abundance in the United States. Proceedings of the National Academy of Sciences 113:140–145.

Long, R. F. and J. Anderson. 2010. Establishing Hedgerows on Farms in California. UC ANR Pub 8390, Oakland, CA. http://anrcatalog.ucanr.edu/Details.aspx?itemNo=8390

Long, R., K. Garbach and L. Morandin. 2017. Hedgerow benefits align with food production and sustainability goals. California Agriculture 71:117-119. 10.3733/ca.2017a0020.

NRC. 2007. Status of Pollinators in North America. National Research Council of the National Academies. National Academies Press, Washington, D.C.. 307 p.

Nordhaus, H. 2011. The Beekeeper's Lament. Harper Perennial, NY. 269p.

Pattemore, D., M. N. Buxton, B. T. Cutting, H. McBrydie, M. Goodwin, A. Dag. 2018. Low overnight temperatures associated with a delay in ‘Hass' avocado (Persea americana) female flower opening leading to nocturnal flowering. Journal of Pollination Ecology 23(14): 127-135.

PHTF: Pollinator Health Task Force. 2015. Pollinator Research Action Plan. The White House.

Sánchez-Bayo, F. and K. A. G. Wyckhuys. 2019. Worldwide decline of the entomofauna: A review of its drivers. Biological Conservation 232:8-27.

Williams, N. M., K. L. Ward, N. Pope, R. Isaacs, J. Wilson, E. A. May, J. Ellis, J. Daniels, A. Pence, K. Ullmann, and J. Peters. 2015. Native wildflower plantings support wild bee abundance and diversity in agricultural landscapes across the United States. Ecological Applications 25: 2119–2131

If you're sticking close to home these days and looking for something to do (or looking for something for kids to do) the Xerces Society has several bee monitoring guides and tools worth checking out.

Developed for conservationists, farmers, land managers, restoration professionals, and community scientists, the Bee Monitoring Protocol and Community Science Guides are useful for documenting how native bee communities change through time in pollinator habitats. The publications include an introduction to bee identification, a detailed monitoring protocol, and data sheets for different habitat types. 

Get The Guides

There is a purpose

Without their keen sense of smell, mosquitoes wouldn't get very far. They rely on this sense to find a host to bite and spots to lay eggs.

And without that sense of smell, mosquitoes could not locate their dominant source of food: nectar from flowers.

"Nectar is an important source of food for all mosquitoes," said Jeffrey Riffell, a professor of biology at the University of Washington. "For male mosquitoes, nectar is their only food source, and female mosquitoes feed on nectar for all but a few days of their lives."

Yet scientists know little about the scents that draw mosquitoes toward certain flowers, or repel them from others. This information could help develop less toxic and better repellents, more effective traps and understand how the mosquito brain responds to sensory information -- including the cues that, on occasion, lead a female mosquito to bite one of us.

Riffell's team, which includes researchers at the UW, Virginia Tech and UC San Diego, has discovered the chemical cues that lead mosquitoes to pollinate a particularly irresistible species of orchid. As they report in a paper published online Dec. 23 in the Proceedings of the National Academy of Sciences, the orchid produces a finely balanced bouquet of chemical compounds that stimulate mosquitoes' sense of smell. On their own, some of these chemicals have either attractive or repressive effects on the mosquito brain. When combined in the same ratio as they're found in the orchid, they draw in mosquitoes as effectively as a real flower. Riffell's team also showed that one of the scent chemicals that repels mosquitoes lights up the same region of the mosquito brain as DEET, a common and controversial mosquito repellant.

Their findings show how environmental cues from flowers can stimulate the mosquito brain as much as a warm-blooded host -- and can draw the mosquito toward a target or send it flying the other direction, said Riffell, who is the senior author of the study.

The blunt-leaf orchid, or Platanthera obtusata, grows in cool, high-latitude climates across the Northern Hemisphere. From field stations in the Okanogan-Wenatchee National Forest in Washington state, Riffell's team verified past research showing that local mosquitoes pollinate this species, but not its close relatives that grow in the same habitat. When researchers covered the flowers with bags -- depriving the mosquitoes of a visual cue for the flower -- the mosquitoes would still land on the bagged flowers and attempt to feed through the canvas. Orchid scent obviously attracted the mosquitoes. To find out why, Riffell's team turned to the individual chemicals that make up the blunt-leaf orchid's scent.

"We often describe 'scent' as if it's one thing -- like the scent of a flower, or the scent of a person," said Riffell. "Scent is actually a complex combination of chemicals -- the scent of a rose consists of more than 300 -- and mosquitoes can detect the individual types of chemicals that make up a scent."

Riffell describes the blunt-leaf orchid's scent as a grassy or musky odor, while its close relatives have a sweeter fragrance. The team used gas chromatography and mass spectroscopy to identify dozens of chemicals in the scents of the Platanthera species. Compared to its relatives, the blunt-leaf orchid's scent contained high amounts of a compound called nonanal, and smaller amounts of another chemical, lilac aldehyde.

Riffell's team also recorded the electrical activity in mosquito antennae, which detect scents. Both nonanal and lilac aldehyde stimulated antennae of mosquitoes that are native to the blunt-leaf orchid's habitat. But these compounds also stimulated the antennae of mosquitoes from other regions, including Anopheles stephensi, which spreads malaria, and Aedes aegypti, which spreads dengue, yellow fever, Zika and other diseases.

Experiments of mosquito behavior showed that both native and non-native mosquitoes preferred a solution of nonanal and lilac aldehyde mixed in the same ratio as found in blunt-leaf flowers. If the researchers omitted lilac aldehyde from the recipe, mosquitoes lost interest. If they added more lilac aldehyde -- at levels found in the blunt-leaf orchid's close relatives -- mosquitoes were indifferent or repelled by the scent.

Using techniques developed in Riffell's lab, they also peered directly into the brains of Aedes increpitus mosquitoes, which overlap with blunt-leaf orchids, and a genetically modified strain of Aedes aegypti previously developed by Riffell and co-author Omar Akbari, an associate professor at UC San Diego. They imaged calcium ions -- signatures of actively firing neurons -- in the antenna lobe, the region of the mosquito brain that processes signals from the antennae.

These brain imaging experiments revealed that nonanal and lilac aldehyde stimulate different parts of the antenna lobe -- and even compete with one another when stimulated: The region that responds to nonanal can suppress activity in the region that responds to lilac aldehyde, and vice versa. Whether this "cross talk" makes a flower attractive or repelling to the mosquito likely depends on the amounts of nonanal and lilac aldehyde in the original scent. Blunt-leaf orchids have a ratio that attracts mosquitoes, while closely related species do not, according to Riffell.

"Mosquitoes are processing the ratio of chemicals, not just the presence or absence of them," said Riffell. "This isn't just important for flower discrimination -- it's also important for how mosquitoes discern between you and I. Human scent is very complex, and what is probably important for attracting or repelling mosquitoes is the ratio of particular chemicals. We know that some people get bit more than others, and maybe a difference in ratio explains why."

The team also discovered that lilac aldehyde stimulates the same region of the antenna lobe as DEET. That region may process "repressive" scents, though further research would need to verify this, said Riffell. It's too soon to tell if lilac aldehyde may someday be an effective mosquito repellant. But if it is, there is an added bonus.

"It smells wonderful," said Riffell.

Mosquitoes are Drawn to Flowers as Much as People

https://www.washington.edu/news/2020/01/21/mosquitoes-flowers/